Polymer Degradation and Stability (v.110, #C)

Lightweight and fire-resistant isocyanate-based polyimide foams (PIFs) were rapidly formed via a simple one-pot process; polymethylene polyphenylene isocyanate (PAPI) was added into a solution containing refilled aromatic dianhydride. The obtained Fourier transform infrared spectra (FT-IR) showed that the refilled 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA) reacted with isocyanate and amino groups in PIFs during the forming and postcuring process. These reactions increased the percentage of polyimide in the foams. Meanwhile, the reaction between refilled BTDA which has a higher reactivity than its derivatives and amino groups, reduced the reaction between isocyanate and amino groups. Subsequently, the generation of ureido was restrained. Thermal gravimetric analysis (TGA) and differential thermogravimetry (DTG) results presented that when the refilled BTDA dosage was increased, the percentage of polyimide and ureido were increased and reduced, respectively. However, the proportion of different ingredients in the PIFs prepared by different formulations was basically the same when the refilled BTDA dosage exceeded 50%. As such, the refilled dosage of BTDA between 50% and 60% was sufficient for this system, the refilled BTDA had extreme effects on enhancing polyimide proportion and reducing the generation of ureido. Fire resistance was characterized by limiting oxygen index (LOI) and cone calorimeter (CCT). Results showed that with the gradual increasing in polyimide proportion of the PIFs resulting from the increase in refilled BTDA dosage, their fire resistance was remarkably improved, which was mainly reflected by the following: gradual increase in LOI value, decrease in heat release rate (HRR), decrease in the peak of HRR (PHRR), decrease in total smoke production (TSP), and decrease in average specific extinction area (ASEA). Compared with the foam prepared without refilled BTDA, the foam prepared with 60% BTDA refilled dosage exhibited increased LOI value from 20.8% to 30.1%, PHRR reduction from 181.91 kW/m2 to 41.54 kW/m2, and significant reduction of HRR. The reduction in TSP and ASEA reached up to 78.2% and 83.1%, respectively. Meanwhile, when the refilled dosage of BTDA exceeded 60%, the LOI value also showed a slower increase. This change was possibly due to the residual BTDA in foams, which acted as a retardant packing role. The density of foams also increased when the post-additive dosage of BTDA was increased. Possible chemical reactions involved in this preparation method of isocyanate-based PIFs were also discussed in this paper.
Keywords: Isocyanate-based polyimide; Foam; Refilled; Fire resistance;

Polyurethane thermal effects studied using two-dimensional correlation infrared spectroscopy by Heliang Sui; Xueyong Liu; Fachun Zhong; Kemei Cheng; Yiwei Luo; Xin Ju (13-22).
Two-dimensional (2D) correlation infrared spectroscopy was used to investigate the thermal effects of polyurethane. Five structure transitions were observed at around 65 °C, 150 °C, 190 °C, 235 °C and 265 °C using moving windows two-dimensional correlation spectroscopy (MW2D). 65 °C and 150 °C were the glass transition temperature of hard segments (HS) and viscous flow temperature, respectively. 190 °C, 235 °C and 265 °C were three thermal degradation temperatures of HS. It was proved that MW2D was sensitive to the polymer structure transitions. The overlapped NH and C=O absorbance bands were identified and analyzed by generalized two-dimensional correlation infrared spectroscopy (2DCOS). The evolvements of the different types of NH and C=O during the transitions were obtained. The results showed 2DCOS could improve the analytical ability of in-situ FITR. Both the two 2D correlation methods are helpful for the polymer degradation mechanism studies.
Keywords: Two-dimensional correlation spectroscopy; Thermal degradation; Polyurethane; In-situ FTIR;

Highly uniform and defect-free multilayer coatings of montmorillonite (MMT) and poly (p-aminostyrene) (PPAS) on Kevlar fibers were generated to provide protection from atomic oxygen (AO) erosion, one of the greatest causes of degradation of polymeric materials used in the low earth orbit. The quantified protective MMT/PPAS layer was successfully deposited through a layer-by-layer assembly technique, as confirmed by Fourier-transform infrared spectroscopy and scanning electron microscopy. The accelerated AO durability was tested in a ground-based AO-effects simulation facility. The results show that the multilayers provide the Kevlar fibers an excellent protection from AO erosion.
Keywords: Kevlar fiber; Nanocomposite assembly; Layer-by-layer assembly; Atomic oxygen resistant coating; Montmorillonite;

In this work, a melamine and cardanol-derived Mannich base polyol (MCMP) was synthesized via a two-step process. First, cardanol was allowed to react with paraformaldehyde melamine and diethanolamine to yield mixed Mannich bases which were subsequently propoxylated to give the MCMP. Rigid polyurethane foams (RPUFs) were prepared using MCMP and a polyisocyanate. Effects of expandable graphite (EG), ammonium polyphosphate (APP) and diethyl ethylphosphate (DEEP) on the flame retardancy, mechanical properties, thermal stability and morphology of the resultant RPUFs were studied. It was demonstrated that the melamine incorporated into the MCMP molecular structure increased the thermal stability and the flame retardancy of the RPUF. The fire resistance of the foam could be further enhanced by the addition of flame retardants. EG is more effective than APP and DEEP in enhancing the limiting oxygen index of MCMP-based RPUFs. The flame-retardant-filled RPUFs display a better compressive strength, thermal stability, char residue, heat release and smoke emission than does the non-filled foams.
Keywords: Cardanol; Melamine; Polyol; Flame retardant; Polyurethane foams;

On the microstructure of polypropylenes by pyrolysis GC–MS by Maria Paola Luda; Riccardo Dall'Anese (35-43).
In this work the pyrolysis products of various Polypropylenes (PP) have been identified in terms of structure and isomerism. The different microstructure of Polypropylenes reflected in the pyrolysis products provides a fingerprint which can be used to asses the origin of the different polymers. The distinction amongst various PP was possible through the quantitative analysis of the main pyrolysis products: 1-alkene pentamers, hexamers and heptamers. After individuation and quantification of these products, a statistic study through the Principal Components Analysis allowed to separate syndio and atactic Polypropylenes as well as isotactic Polypropylenes of different origin. The results of this study can be used in various fields, for example in forensic and commodities analyses or in quality control.
Keywords: Polypropylene; Pyrolysis products; Tacticity; Pyrolysis-GC-MS; Principal component analysis;

Poly[(R)-lactate-co-(R)-3-hydroxybutyrate] [P(LA-co-3HB)] is a biobased polyester with semitransparent and flexible properties produced in engineered bacteria carrying an LA-polymerizing enzyme. In this study, we attempted to isolate the P(enriched LA-co-3HB)-degrading bacteria from soil samples in order to identify enzymes with the capacity to degrade this new type of polymer. Among approximately 500 samples, the Gram-negative bacterium C34, which exhibited potent P(enriched LA-co-3HB)-degrading activity, was isolated based on the decrease in the turbidity of culture medium supplemented with emulsified P(67 mol% LA-co-3HB). Based on its 16S rDNA sequence, this isolated bacterium was identified as a member of Variovorax sp.. Next, we attempted to isolate and purify the depolymerase that contributes to the polymer degradation from the culture supernatant of strain C34. The purified enzyme had a molecular mass of 42 kDa and exhibited degradation activity towards the P(67 mol% LA-co-3HB) as well as 3HB homopolymer [P(3HB)], but not LA homopolymers (PDLA and PLLA). On the other hand, a well-characterized depolymerase of P(3HB) derived from Alcaligenes faecalis T1 did not degrade P(67 mol% LA-co-3HB), PDLA or PLLA. This result suggests that the newly isolated depolymerase differs from the P(3HB) depolymerase from A. faecalis.
Keywords: Lactate-based polymer; Polyhydroxyalkanoate; Enzyme; Biodegradation;

Novel poly(xylitol sebacate)/hydroxyapatite bio-nanocomposites via one-step synthesis by Piming Ma; Ting Li; Wei Wu; Dongjian Shi; Fang Duan; Huiyu Bai; Weifu Dong; Mingqing Chen (50-55).
Novel poly(xylitol sebacate) elastomer/nano-hydroxyapatite (PXS/n-HA) bio-nanocomposites have been fabricated by melt polycondensation of xylitol and sebacic acid in the presence of n-HA. The mechanical properties of the PXS, e.g. tensile strength and elongation at break, were significantly increased by the in situ addition of n-HA. Differential scanning calorimetry (DSC) results revealed that the glass-transition temperatures of PXS were decreased by introduction of n-HA while the thermogravimetric analysis (TGA) indicated an improved thermal stability of the PXS/n-HA bio-nanocomposites in comparison with PXS. SEM and TEM images showed good dispersion and distribution of n-HA in the PXS matrix. In addition, the introduction of n-HA improved the hydrophilicity and decreased the in vitro degradation rate of the PXS.
Keywords: Xylitol; Hydroxyapatite; Elastomer; Bio-nanocomposites;

Pros and cons of melt annealing on the properties of MWCNT/polypropylene composites by Gennaro Gentile; Veronica Ambrogi; Pierfrancesco Cerruti; Rosa Di Maio; Giuseppe Nasti; Cosimo Carfagna (56-64).
The combined effect of melt annealing and surface modification of multiwalled carbon nanotubes (MWCNT) on polypropylene (PP) based nanocomposites is reported. Melt annealing markedly improved the filler dispersion in PP. The rheological and electrical percolative threshold was achieved at a content of 3 wt% MWCNT, due to the dynamic reconstruction of nanotube network in the polymer matrix. This behaviour was particularly evident in the case of surface-modified MWCNT. However, the heat treatment also induced an overall worsening of mechanical properties due to polymer heterogeneous oxidation at a microscopic scale, as detected by oxygen mapping through SEM/EDS. Crack initiation sites eventually leading to the failure of the polymer were formed due to peroxide-mediated spreading of oxidation, radiating from residual polymerisation catalyst particles. FTIR-ATR spectroscopy demonstrated that blooming of the phenol stabilizer due to thermal annealing was responsible for early oxidation of polypropylene. The reported results highlight the advantages and drawbacks of physical strategies designed to improve the dispersion stability of nanotubes in polymer nanocomposites.
Keywords: Polypropylene; Multiwalled carbon nanotubes; Heat treatment; Rheological properties; Electrical properties; Thermal oxidation;

Hydrolysis of poly(lactic acid) into calcium lactate using ionic liquid [Bmim][OAc] for chemical recycling by Xiuyan Song; Hui Wang; Xuequn Yang; Fusheng Liu; Shitao Yu; Shiwei Liu (65-70).
Hydrolysis of poly(lactic acid) (PLA) to calcium lactate was studied using an ionic liquid catalyst, 1-butyl-3-methylimidazolium acetate [Bmim][OAc], to develop a chemical recycling process for waste PLA. The influences of experimental parameters, such as reaction time, reaction temperature, [Bmim][OAc] dosage and water dosage on the hydrolysis results of PLA were examined. A study on reusability of the ionic liquid showed that it could be reused up to 7 times with no noticeable decrease in the hydrolysis conversion of PLA and the yield of calcium lactate. A mechanism of PLA hydrolysis in [Bmim][OAc] was proposed. In addition, the kinetics of this reaction was investigated. The results demonstrated that the hydrolysis process was a first-order kinetic reaction in the presence of [Bmim][OAc] and the activation energy is 133.9 kJ/mol.
Keywords: Hydrolysis; Poly(lactic acid); Ionic liquid; Chemical recycling;

Study on bacterial poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB4HB)) thermal degradation employing mild reaction conditions and carboxylate salt is described. The chemical structure of the obtained oligomers was determined with the aid of 1H NMR and ESI-mass spectrometry techniques. The comparison of a non-volatile degradation products obtained via carboxylate-induced thermal degradation of the P(3HB4HB) with products of the model polymer pyrolysis revealed significant differences in structure of the resulting oligomers. Exclusive formation of linear oligomers terminated with unsaturated, on one end, and carboxyl, on the other end, groups was noticed in case of base-catalyzed degradation contrary to oligomers produced via pyrolysis which contained also macrocyclic structures and γ-butyrolactone. Moreover, the elaborated method demonstrates the ability to produce well-defined oligomers with controlled molar mass. The resulting oligomers have huge potential as macroinitiators or macromonomers and can be useful for further synthesis of more sophisticated polymeric materials.
Keywords: Poly(3-hydroxybutyrate-co-4-hydroxybutyrate); Carboxylate induced degradation; E1cB mechanism; 3HB4HB oligoesters;

Modeling the pH-dependent PLA oligomer degradation kinetics by S. Lazzari; F. Codari; G. Storti; M. Morbidelli; D. Moscatelli (80-90).
The hydrolysis of lactic acid oligomers involves several different reactions, acid-catalyzed, base-catalyzed as well as non-catalyzed. In the present paper a pH-dependent kinetic model has been developed and its kinetic constants evaluated by fitting to experimental data of degrading lactic acid oligomers at 37 °C in aqueous solution at pH = 1, 2, 3.5, 5.7 and 7.4. The model was able to properly describe the experimental data with an average error of about 5%. The estimated values of the kinetic constants at the selected temperature are: k D α = 4.44 × 10 − 3 L 2 mol − 2 h − 1 , k D β = 9.29 × 10 − 4 L 2 mol − 2 h − 1 (acid-catalyzed), k RH = 1.56 × 10 3 L 2 mol − 2 h − 1 , k BB = 2.88 × 10 6 Lmol − 1 h − 1 (base-catalyzed) and k W = 2.49 × 10 − 5 Lmol − 1 h − 1 (non-catalyzed).
Keywords: Biopolymer; Lactic acid; Degradation; Hydrolysis; pH;

Intumescent coating is an insulating material designed to decrease heat transfer to a substrate structure. This research presents the results of different formulations developed to study the effects of kaolin clay on expansion of coating and heat shielding during the fire test. The intumescent coating formulations (ICFs) were tested at 950 °C for 1 h. The results showed that the coatings were stable and well bound with substrate. The coatings were characterized by using Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The morphology of char was studied by FESEM on the coating after fire test. XRD and FTIR showed the presence of carbon (graphite), boron phosphate, boron oxide, sassolite and kaolinite in the residual char. TGA showed that kaolin clay reinforced formulation; IF5-KC enhanced 49% residual weight than that of IF-Control formulation. XPS analysis showed that elemental composition of IF5-KC char residue gave 41.80% carbon content in the residual char. An accelerated weathering test ASTM D 6695-03 showed that IF5-KC coating sustained its integrity up to 90 days under accelerated weathering chamber.
Keywords: Intumescent fire retardants; Heat shielding; FESEM; TGA; FTIR;

In this article, a hyperbranched poly(phosphamide ester) oligomer HBPE was prepared via A3 + BB′ method. FTIR spectrum, 1H and 31P NMR spectrum and GPC were utilized to characterize HBPE. Then HBPE was melt blended with PLA to fabricate flame retardant PLA composites. The integrated flame retardant property of PLA composites was investigated by LOI, UL-94, pyrolysis combustion flow calorimeter test (PCFC) and cone calorimeter test (CCT). The thermal stability of PLA composites was investigated by TGA, weight loss difference analysis and integral procedural decomposition temperature (IPDT). Results showed that PLA composite with only 2 wt% HBPE exhibited excellent flame retardancy (LOI = 33% and UL-94 V-0 rating) and 10 wt% HBPE imparted PLA composites largely increased LOI value of 43%. The incorporation of 10 wt% HBPE increased CO production rate (COP) and prolonged time to ignition (TTI) in CCT. Furthermore the thermal stability of PLA composites was enhanced from IPDT analysis. Meanwhile, DSC analysis of PLA composites showed T g of PLA composites decreased slightly with the addition of HBPE, which indicated the limited plasticizing ability of HBPE in PLA composites. Finally, the accelerated nucleation effect was also detected in PLA composites using POM observation. Results showed HBPE was a high-effective flame retardant of PLA, exhibiting good nucleating property and limited plasticizing ability in PLA composites.
Keywords: PLA; Hyperbranched poly(phosphamide ester) oligmer; Flame retardancy; Synergistic carbonization;

The uptake of synovial lipids into ultra high molecular weight polyethylene (UHMWPE) has been recently related with the in vivo and ex vivo oxidation of irradiated and remelted UHMWPE. Natural polyphenols have been demonstrated effective in protecting highly crosslinked UHMWPE from oxidation. This manuscript aims to investigate how squalene as a model unsaturated lipid affects the oxidative stability of polyphenol-stabilized highly crosslinked UHMWPE. The irradiated UHMWPE showed less squalene uptake and diffusion in comparison to the unirradiated UHMWPE due to the crosslinked structures in the former. Upon accelerated aging at 70 °C and 5 atm O2 for different durations, the presence of squalene significantly accelerated the initiation, development and propagation of oxidation for the virgin and irradiated UHMWPE. The presence of antioxidants including natural polyphenols effectively prosponded and reduced oxidation of the squalene-doped irradiated UHMWPEs. The oxidation levels and depth of irradiated antioxidant/UHMWPE blends were much less than those for the irradiated UHMWPE. It is concluded that the natural polyphenols are effective in prohibiting oxidation related to the presence of squalene. This finding may be of clinical relevance in terms of stabilization of irradiated UHMWPE against synovial lipids-related oxidation.
Keywords: UHMWPE; Lipid; Oxidation; Polyphenol; Irradiation;

Bioresorbable highly porous polymer scaffolds play a pivotal role in tissue engineering applications. Ideally, the degradation rate of these scaffolds should match the tissue regeneration rate so that there is a gradual transfer of mechanical loads from the scaffold to the regenerated tissue. In this study the degradation behavior of porous and non-porous poly(l-lactide) (PLLA), poly(ε-caprolactone) (PCL) and poly(lactide-co-ε-caprolactone) (PLCL) in phosphate buffered saline (PBS) at 37 °C for a period up to 18 weeks was investigated. The calculated degradation rates (K Mw) of the samples studied, from the fastest to the slowest, was: PLCL > PLLA > PCL. On the other hand, the porous structures displayed slower degradation rates with respect to their non-porous counterparts. Finally, the bioactivity of a porous PLLA scaffold filled with 0, 15 and 30 vol.% of bioactive glass particles was confirmed by the deposition of an apatite layer on the surface of the material. Even in the scaffold filled with 15 vol.% of bioactive glass particles the precipitation of the apatite layer was observed in 14 days, whereas in the scaffold with 30 vol.% of bioactive glass this layer appeared just 3 days after being submerged in simulated body fluid (SBF).
Keywords: Poly(l-lactide); Poly(ε-caprolactone); Poly(lactide-co-ε-caprolactone); Hydrolytic degradation; Bioactive glass;

The long-term stability of poly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene]vinylene} (MEH-PPV) in solutions exposed to air at daylight and in the dark at room temperature has been studied using the size exclusion chromatography (SEC), UV/vis, fluorescence and IR spectra of aged samples, and comparison of UV/vis spectra of SEC fractions. Solvents currently used in the preparation, analysis and processing of MEH-PPV were used: tetrahydrofuran (THF), chloroform (CHCl3) and chlorobenzene (PhCl). The SEC-DAD data revealed a serious decrease in the delocalization of electrons in MEH-PPV chains, even in the large ones, which proves a deep damage to the structure of the chains prior to their cleavage. The IR spectra of aged samples show that the saturation of main-chain double bonds and the changes in the substitution of phenylene rings are the main chemical structure defects present in chains of aged MEH-PPV. The rate as well as the extent of the overall degradation process is ca ten to fifty times enhanced by the ordinary daylight. The rate of cleavage and the damage to the structure of MEH-PPV molecules are significantly influenced by the choice of the solvent; they increase in the order: PhCl < CHCl3 < THF. PhCl can be recommended as one of the best solvents for MEH-PPV processing from solutions.
Keywords: Aging; Conjugated polymers; Degradation; Daylight effect; Solvent effect;

Influence of exfoliated graphite nanoplatelets on the flammability and thermal properties of polyethylene terephthalate/polypropylene nanocomposites by I.M. Inuwa; Azman Hassan; De-Yi Wang; S.A. Samsudin; M.K. Mohamad Haafiz; S.L. Wong; M. Jawaid (137-148).
Nanocomposites based polyethylene terephthalate (PET)/polypropylene (PP) (70/30 wt%) blends and exfoliated graphite nanoplatelets (GNP) as reinforcing fillers were developed using melt extrusion process. The filler concentration was varied between 0 -5.98 wt percent (%) (0–7 phr). The resulting nanocomposites were characterized in terms of flame retardancy, thermal conductivity, thermal behavior, morphology and structure. Cone calorimeter analysis, limiting oxygen index (LOI) and UL94 flame rating tests revealed that addition of GNPs to PET/PP improved the flame retardancy of PET/PP/GNP nanocomposites significantly. Cone calorimeter data show a significant reduction of peak heat release rate (PHRR), mass loss rate and delayed time to ignition (TTI) due to addition of GNPs to PET/PP blend. As much as 37% reduction in PHRR and 32% increase in TTI were observed for the maximum GNP loading. Enhancements of flammability properties were attributed to the development of compact, dense, uniform char layers on the surface of nanocomposites. The effective thermal conductivity was found to vary linearly with GNP loading which was attributed to the formation of effective interconnected heat conduction bridges formed by the GNPs. It was found that the effective thermal conductivity of the nanocomposites was increased by about 80%, i.e. from 1.2 W/m.K for the unreinforced PET/PP blend to 1.9 W/m K for the 5.98 wt% (7 phr) reinforced PET/PP/GNP nanocomposites. Differential scanning calorimetry results indicated that the addition of GNPs increased crystallization temperatures but decreased degree of crystallinity of PET/PP/GNP nanocomposites. However; the melting points remained essentially unaffected. Transmission electron microscopy and field emission scanning electron microscopy showed uniform dispersion of GNPs in the matrix with the formation of interconnected GNP sheets at 3 phr. Isolated instances of exfoliation of GNPs was also observed.
Keywords: Flame retardancy; Thermal conductivity; Exfoliated graphite nanoplatelets crystallization temperatures; Polyethylene terephthalate (PET); Polypropylene (PP);

Synthesis, recyclability, and physical properties of poly(l-lactide) (PLLA)-based network polymers prepared by means of Diels–Alder (DA) reaction between bisfuranic terminated PLLA prepolymers (PLLA n F2-x; degree of polymerization, n = 35–59, substituent in the vicinity of furan, x = amide or ester) and a tris-maleimide cross-linker (M3) are described. Molecular weight of prepolymer and substituent in the vicinity of furan rings are strongly effective in equilibrium control of DA and retro-DA reactions between PLLA n F2-x and M3. Lower molecular weight of the prepolymer and amide-substitution in the vicinity of furans significantly enhance the reactivity between PLLA n F2-x and M3, resulting in more perfect network structure, completely suppressed crystallinity, and much better mechanical properties of the PLLA-based DA network polymers. The PLLA-based DA network polymer containing numerous thermoreversible covalent bonds is a promising material as a readily recyclable biobased polymeric material.
Keywords: Poly(l-lactide); Biobased plastics; Diels–Alder reaction; Equilibrium control; Polymer recycling;

Degradation of poly(l-lactide) under KrF excimer laser treatment by Bogusz D. Stępak; Arkadiusz J. Antończak; Konrad Szustakiewicz; Paweł E. Kozioł; Krzysztof M. Abramski (156-164).
In this paper, the authors present an impact of the KrF excimer laser irradiation above the ablation threshold on physicochemical properties of biodegradable poly(l-lactide). The analysis for the high energy density range is crucial in evaluating to what extent polymer degrades during erosive material removal. This approach was not presented in the available literature. The laser treated samples were analysed by means of Differential Scanning Calorimetry (DSC) and Gel Permeation Chromatography (GPC) which were helpful to characterize the bulk modifications. The surface affected by laser ablation was analysed using infrared spectroscopy (Attenuated Total Reflectance) as well as X-ray Photoelectron Spectroscopy. The techniques used gave a complex image of changes introduced into the material. The ablation of polylactide surface resulted in a decrease of molecular weight within an entire irradiated volume of ∼250 μm thick polymer sheet. The increase of polydispersity was also noted. Both DSC and GPC techniques show that in spite of different laser fluence, the extent of degradation is similar for all laser ablated samples. The XPS analysis revealed no oxidation of the surface. The appearance of vinyl and ketone unsaturated groups as well as carboxyl terminals after laser treatment was revealed by FTIR spectroscopy. The presence of new functional groups is a result of photochemical or/and thermal processes which both yield similar degradation products.
Keywords: poly(l-lactide); KrF excimer laser; Ablation; GPC; DSC; FTIR-ATR;

One-pot synthesis of a novel s-triazine-based hyperbranched charring foaming agent and its enhancement on flame retardancy and water resistance of polypropylene by Panyue Wen; Xiaofeng Wang; Bibo Wang; Bihe Yuan; Keqing Zhou; Lei Song; Yuan Hu; Richard K.K. Yuen (165-174).
A novel hyperbranched charring foaming agent (HCFA), successfully prepared via an A2B3 approach with about 97% yield, was combined with ammonium polyphosphate (APP) to flame-retard polypropylene (PP) at a 30 wt% loading. The results of thermogravimetric analyses of various PP samples in air and nitrogen showed that the HCFA/APP system could effectively improve the thermal and thermal-oxidative stabilities of the char residues. And PP3 with a 3/1 mass ratio of APP to HCFA left the highest amount of char residue at 800 °C. The studies of their flammability revealed that the addition of HCFA can make great contribution to the increase of the limiting oxygen index and the UL-94 V0 rating, and the decrease of the heat release rate (HRR) and fire growth index (FGI) of PP/APP/HCFA composites relative to PP with 30 wt% APP. The investigation of their water resistance demonstrated that the PP composites with a mass ratio of APP to HCFA being between 3:1 and 1:1 still obtained a UL-94 V-0 rating after 168 h soaking in hot water, due to the delayed migration of intumescent flame retardant from the complexation between hydrophilic APP and hydrophobic HCFA. Besides, their mechanical properties were also investigated.
Keywords: Polypropylene; Hyperbranched charring foaming agent; Flame retardance; Thermal stability; Water resistance;

Influence of PE/PP ratio and ENB content on the degradation kinetics of γ-irradiated EPDM by A. De Almeida; L. Chazeau; G. Vigier; G. Marque; Y. Goutille (175-183).
Different Ethylene Propylene Diene Monomers have been characterized prior and after aging under γ-irradiation. At small irradiation doses, the crosslinking process is the main mechanism occurring during irradiation, and is related to the residual ENB units remaining after the material processing. At higher doses, chain scissions (proportional to the radiation dose) are predominant and can be considered independent on the PE/PP ratio at a given ENB ratio, on the residual peroxide content, and on the initial EPDM cross-links density.
Keywords: Elastomer; Lifetime; Degradation; Statistical model;

Physicochemical characterization of ethanol organosolv lignin (EOL) from Eucalyptus globulus: Effect of extraction conditions on the molecular structure by Mauricio Yáñez-S; Betty Matsuhiro; Carolina Nuñez; Shaobo Pan; Christopher A. Hubbell; Poulomi Sannigrahi; Arthur J. Ragauskas (184-194).
The aim of the present study was to investigate the effect of extraction conditions, mainly severity factor (H-factor = 3980–14,500) on the molecular structure of ethanol organosolv lignins extracted from Eucalyptus globulus. Isolated lignins were structurally characterized by 1H NMR, 31P NMR, UV–Vis, FT-IR spectroscopy and gel permeation chromatography. The results showed that an increase in the severity of the pretreatment decreased the molecular weight of the lignins within a 36–56% range with respect to the untreated lignin (MWL). Moreover, the increase in severity of the organosolv treatment was accompanied by strong decrease in the content of aliphatic hydroxyl groups and by an increase of syringyl phenolic units and condensed phenolic structures. The condensed phenolic structures quantified in the organosolv lignin correspond to resinol, phenylcoumaran, dibenzodioxocin, spirodienone and β-1′ linkages.
Keywords: Organosolv; Lignin; Lignocellulosic; Eucalyptus;

Ablation and thermo-mechanical investigation of short carbon fiber impregnated elastomeric ablatives for ultrahigh temperature applications by M. Bassyouni; Nadeem Iqbal; Sadia Sagar Iqbal; S.M.-S. Abdel-hamid; M.H. Abdel-Aziz; Umair Javaid; Mohammad Bilal Khan (195-202).
Elastomeric ablative composites for ultrahigh temperature applications were processed and characterized to elucidate the potential of short carbon fibers (SCF) to tailor the thermo-mechanical and ablation characteristics of acrylonitrile butadiene rubber (NBR) composites. SCF was dispersed within NBR using dispersion kneader and two roller mixing mill. Ablation and thermal properties versus back-face temperature elevation during oxy-acetylene flame test, linear/radial ablation rates, percent char yields, insulation index, and thermal conductivity of the fabricated ablatives were measured. Experimental results revealed that the thermo-mechanical and ablation characteristics were significantly improved with increasing SCF concentration in the presence of coupling agent. Improvement in tensile strength, hardness and reduction in elongation at break were obtained with increasing SCF to matrix ratio. The microscopic analysis of the tensile fracture and ablation specimen showed the porosity generation during ablation and uniform dispersion of the impregnated SCF in NBR.
Keywords: Polymer-matrix composites (PMCs); Thermal properties; Mechanical testing; Mechanical properties; High temperature properties;

Two different types of biodegradable polymers and polymer composites, namely Ecovio® reinforced by 30 wt% wood-flour, and flax/starch composites prepared elsewhere, were analyzed experimentally and theoretically. The monotonic loading, stress-relaxation and creep-recovery experiments revealed a highly nonlinear viscoelastic/viscoplastic response. This behavior was treated by a three-dimensional constitutive model, analytically presented in a previous work. The model presumes that the materials follow a nonlinear viscoelastic path, while later on viscoplasticity prevails. The combination of the transient network model, related to the viscoelasticity, with a plasticity theory, lead to a constitutive model, which was proved to be capable of describing the experimental data of stress-relaxation, monotonic loading and creep-recovery in a unified manner. Deviations, which were detected for the first material types, requiring new parameter values, were attributed to structural changes arising from creep-recovery experiment.
Keywords: Biobased materials; Creep; Nonlinear viscoelastic; Viscoplastic;

Thermogravimetric analyses under air atmosphere were performed up to 973 K on balsa wood to investigate the thermal degradation process of two types of samples aged differently: a dry balsa specimen and a hygroscopically aged material. The Kissinger method was used to determinate the kinetic parameters as the activation energy Ea, the pre-exponential factor k 0 and the order of reaction n. The three constituents of balsa (i.e. hemicellulose, cellulose and lignin) were well identified and the decomposition temperature region well characterized. The presence of a large quantity of water affects the thermal decomposition behavior of wood inducing notably a maximal degradation temperature higher by 314 K in relation to the dry material. The determined experimental kinetic parameters Ea, k 0 and n are in good agreement with those find in the literature for woods. The role of diffused water in the different thermal behavior between dry and aged balsa is explained from physical and chemical points of view.
Keywords: Composite materials; Balsa wood; Durability; Thermal degradation; Fire; Thermogravimetric analysis (TGA);

In the present article, a pultruded basalt fiber-reinforced polymer (BFRP) plate was thermally aged at 135 °C and 300 °C for 4 h, and the aged BFRPs were sequentially immersed in distilled water and strong alkaline solution (pH = 13.5) at 20, 40 and 60 °C for six months. The moisture uptake behaviors due to thermal aging were investigated. As found, thermal aging at 300 °C brought in many voids, and obvious degradation of the cross-linking density (ρ) of the epoxy matrix due to thermal decomposition. Further immersion in alkaline solution leads to additional cracks and more serious hydrolysis of the matrix. Aging at 135 °C causes post-curing of the resin matrix, but deteriorates the bonding behavior between fiber and resin matrix, which is indicated by the enhanced coefficient of diffusion (D) along fiber directions. Two-stage water diffusion model can describe the water uptake process for aged and un-aged BFRPs efficiently. D along and perpendicular to the fibers are determined theoretically and experimentally. Due to the cracks, voids as well as fiber debonding occurred in the thermal aged BFRPs, much increased Ds, lowered activation energy for diffusion and even mass loss (in high temperature alkaline solution) were found.
Keywords: Thermal aging; Basalt fiber reinforced polymer; Moisture uptake; Coefficient of diffusion;

Polymer flooding in high temperature reservoirs usually has shown poor performance because the injected polymeric solution tends to experience severe thermal degradation and ineffective in-situ sweep behavior. For the simulation results under such reservoirs, the real observation is likely to be out of estimation due to the absence of accurate viscosity model. The aim of this study was therefore to modify an existing numerical reservoir simulator to model HPAM hydrolysis, which is caused by thermal degradation in high temperature reservoirs, by employing the concept of half-life decomposition. The term ‘half-life’ has been proposed in numerical simulations to describe the kinetics of thermal decomposition of unstable polymers. This work analyzed rheological properties considering thermal hydrolysis with the goal of establishing an in-situ viscosity calculation for high temperature reservoirs. Comparison of the conventional Flory–Huggins’ model to the proposed viscosity model allowed us to evaluate hydrolysis and the long-term stability of the polymer according to temperature. The results obtained using the new viscosity model indicated that polymer concentration loss was proportional to the initial concentration. However, viscosity reduction was more severe than concentration loss at higher initial polymer injection concentrations and was exaggerated as the initial concentration increased. Due to polymer decomposition at high temperatures, application of polymer flooding is limited at high-temperature reservoir.
Keywords: Polymer flooding; Thermal degradation; Hydrolysis; Half-life; Viscosity model;

Study of the stability of siloxane stone strengthening agents by Elena Tesser; Fabrizio Antonelli; Laura Sperni; Renzo Ganzerla; Noni-Pagona Maravelaki (232-240).
The commercial organosilicone compounds Rhodorsil Consolidante RC90 and Rhodorsil Consolidante RC80, commonly used as stone strengthening agents for the conservation of artefacts, were tested to ascertain their chemical nature, the mechanisms involved in the polymerization reactions and their stability under oxidative stress. The resins were first chemically characterized by means of GC/MS, FTIR and EDXRF techniques, then applied to slides and subjected to controlled photo-oxidative and thermo-oxidative weathering. The film's morphology was observed by SEM determinations, while DTA-TG techniques were used to determine polymer thermal stability. The features examined prompted a number of considerations on the effects of the resins applied on stone materials and were the reference point for speculation on the chemical nature and the performance of Sogesil XR893, a silicon resin which is no longer available on the market.
Keywords: Silicone resin; Hydrolysis; Photo-oxidation; Thermal stability; Stone conservation;

Further progress into the thermal characterization of HCN polymers by José L. de la Fuente; Marta Ruiz-Bermejo; Delphine Nna-Mvondo; Robert D. Minard (241-251).
In order to further investigate the thermal characterization of hydrogen cyanide polymers, in this study we focus on the thermogravimetry (TG) of three polymer samples obtained from different synthetic routes. The first one was synthesized from an aqueous solution of equimolar amounts of sodium cyanide (NH4Cl) and ammonium chloride (NaCN). The second one was produced from the polymerization of HCN gas in water, HCN being obtained from the reaction of NH3, CH4 and air over a platinum catalyst at 1100 °C; and the last sample was synthesized from anhydrous HCN, produced by the action of sulfuric acid on sodium cyanide. Differential thermal analysis (DTA), differential scanning calorimetry (DSC) and a coupled TG-mass spectrometer (MS) were used to evaluate the thermal behavior of these black polymers, which are of significant interest in prebiotic chemistry but also in extraterrestrial chemistry. All the samples present a similar thermal behavior. Following a dehydration process, three pyrolysis stages are observed, which occur over the temperature ranges of 150–300 °C, 300–550 °C and above 550 °C. However, we observe that the char-forming reactions at higher temperatures, in the carbonization stage, is strongly dependent on the HCN polymer sample and the presence or absence of oxygen. During each stage, the same volatilization processes take place regardless of the type of HCN polymer sample. Deamination and dehydration reactions dominate in the low temperature range while thermal depolymerization, releasing HCN, and a denitrogenation process occur mainly at elevated temperatures. The release of isocyanic acid (or cyanic acid) and formamide are also identified within a wide range of temperatures. We discuss and interpret the thermal decomposition behavior to be related to the polymerization mechanisms in accordance with recent studies.We outline that the thermal profiles could be a good fingerprint of this complex macromolecular prebiotic material, whose structure still remains uncertain, despite of their intensive studies over the last fifty years.
Keywords: HCN polymers; Coupled TG–MS; Thermal decomposition; DSC; DTG;

An intumescent fire retardant (IFR) system based on guanidine phosphate (GP) and pentaerythritol (PER) was proposed. Decomposition products of GP were studied by thermogravimetric analysis (TGA) combined with pyrolysis gas chromatography-mass spectrometry (Pyrolysis GC–MS) at first. The pure intumescent fire retardant (IFR) GP-PER was studied then. When the IFR was combusted, the special spherical shell-shaped foam was generated. The foam was made up of soluble phosphorus degradation products (PDPs) and insoluble nitrogenous - carbonaceous char consisting of fused ring and heterocyclic ring structures derived from the degradation products of pentaerythritol phosphate esters and condensed cyanamide derivatives. Scanning electron microscopy (SEM) and Raman spectroscopy as well as Ion chromatography (IC) and elemental analysis were used to study the morphology and the moieties of the foam. The mechanism of the special foam formation was proposed with the help of TGA results in the paper. Eventually, mixtures of this IFR blended in polypropylene (PP) matrix were prepared and the fire retardancy was studied. Fourier transform infrared spectroscopy (FTIR) indicated the variation of the foam moieties from 270 °C to 500 °C. Experiments proved the optimal mass ratio of GP and PER is 2:1 to get fire retardancy in PP matrix. With an addition of 25 wt%, the limited oxygen index (LOI) could reach 31% and vertical burning ratings (UL-94 tests) reach a V-0 rating.
Keywords: Guanidine phosphate; Thermal decomposition; Cyanamide derivatives; Spherical shell-shaped foam; Mechanism; Fire retardancy;

Preparation of silica-supported 2-mercaptobenzimidazole and its antioxidative behavior in styrene-butadiene rubber by Bangchao Zhong; Qifeng Shi; Zhixin Jia; Yuanfang Luo; Yongjun Chen; Demin Jia (260-267).
A novel type of rubber antioxidant, silica-supported 2-mercaptobenzimidazole (SiO2-s-MB), was prepared by reacting 2-mercaptobenzimidazole (MB) with chlorosilane-modified silica (m-SiO2). Raman spectroscopy, FT-IR, XPS and TGA confirmed that MB was chemically bonded onto the surfaces of silica particles. SEM observation showed that SiO2-s-MB was homogeneously dispersed in the styrene-butadiene rubber (SBR) matrix. Based on the measurement of oxidation induction time (OIT) of SBR/SiO2-s-MB and SBR/m-SiO2/MB composites containing equivalent antioxidant components, it was found that the antioxidative efficiency of SiO2-s-MB was superior to that of the corresponding low molecular MB. By determining the changes of tensile strength, elongation at break and crosslinking density of SBR composites during long-term accelerated aging, it was shown that the thermal oxidative stability of SBR/SiO2-s-MB composites was much higher than that of SBR/m-SiO2/MB composites. Furthermore, the color contamination, migration and volatility of SiO2-s-MB were lower than those of MB, indicating that SiO2-s-MB is environmentally friendly.
Keywords: 2-Mercaptobenzimidazole; Silica; Styrene-butadiene rubber; Antioxidative behavior;

The poly(ethylene terephalate)(PET)/hexakis [p-(hydroxymethyl)phenoxy] cyclotriphosphazene (PN6)/poly(2-phenylpropyl) methylsiloxane (PPPMS) composites were prepared, the flame-retardancy and anti-dripping properties were also investigated. The results indicated that the contents of PN6 and PPPMS had great effect on the melt behavior, crystallization and thermal properties of PET composite. The introducing of PN6 and PPPMS into PET would accelerate the char formation and anti-dripping during the flame-retardant PET combustion process. The analysis of morphology and chemical components of the charred residue displayed a synergistic effect of the PET/PN6/PPPMS system by providing a compact and intact barrier and promoting the accumulation of silicon elements in the outer surface of char residues.
Keywords: PET; Hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene; Poly(2-phenylpropyl) methylsiloxane; Flame-retardancy; Anti-dripping;

The anaerobic biodegradability of four bioplastics powders (125–250 μm), polycaprolactone (PCL), poly(lactic acid) (PLA), polyhydroxybutyrate (PHB) and poly(butylene succinate) (PBS), were compared at 37 °C under aquatic conditions using our previously reported evaluation system (the modified ISO 13975 method). The bioplastics were ranked PHB >> PLA > PCL in terms of anaerobic biodegradation rate. The biodegradability of PHB, PLA, and PCL was 90% in 9 days, 29% and 49% in 277 days, and 3% and 22% in 277 days, respectively. PBS could not be anaerobically biodegraded by the sludge used in this study. The eubacteria and archaea participating in anaerobic bioplastic biodegradation were detected using the RT-PCR DGGE method. Some eubacteria participating in anaerobic biodegradation of PCL and PLA were of unique character. Eubacteria involved in anaerobic biodegradation of PHB were 98% homologous with Arcobacter thereius, Clostridium sp, and Clostridium sp, respectively. The eubacteria involved in the anaerobic biodegradation of PLA were 100% identical to Xanthomonadaceae bacterium and Mesorhizobium sp.; however, the other three bacterium were poorly related (<95% similarity) to any of the cultured-bacterium or database sequences. Anaerobic biodegradation of PCL was conducted by eubacterium with 98% similarity to A thereius, and by five organisms with poor similarity (≤95%) to any of the cultured-bacterium or database sequences. Archaea involved in anaerobic biodegradation of PLA and PCL were 97% and 95% identical to Methanosaeta concilii and Methanobacterium petrolearium. Only faint bands were observed in the RT-PCR DGGE profile of the archaea generated during PHB anaerobic biodegradation.
Keywords: Anaerobic biodegradation; Methane fermentation; RT-PCR DGGE; Bioplastic; ISO 13975;

Lipase mediated enzymatic degradation of polydioxanone in solution by Aditi Banerjee; Kaushik Chatterjee; Giridhar Madras (284-289).
The enzymatic biodegradation of polydioxanone (PDO) in trifluoroethanol (TFE) at various temperatures (25–55 °C) was studied with two different types of lipases, namely immobilized enzyme Novozym 435 and free enzyme porcine pancreas lipase. The biodegradation process was monitored by gel permeation chromatography (GPC). Both enzymes showed the optimum activity at 37 °C and Novozym 435 exhibited better thermal stability over the experimental temperature range. A continuous distribution kinetic model was employed to describe the biodegradation process and the model was used to fit the experimental data satisfactorily and obtain kinetic parameters.
Keywords: Polydioxanone; Degradation; Lipase; Distribution kinetics; Reaction rates;

The potential of metal oxalates as novel flame retardants and synergists for engineering polymers by A.F. Holdsworth; A.R. Horrocks; B.K. Kandola; D. Price (290-297).
Based on their known decomposition to carbon dioxide, carbon monoxide and the respective oxide, six metal (calcium, manganese (II), iron (II), copper (II), tin (II) and zinc) were synthesised and assessed for their potential flame retardant activity in the absence and presence of selected flame retardants. Initially they were assessed when impregnated on cotton as a screening process and then selectively compounded with polyamide 6.6 (PA66), as a typical engineering polymer. Only manganese (II) and iron (II) oxalates alone reduced the burning rate of cotton, whereas together with ammonium bromide, calcium and iron (II) oxalates showed an apparent additional burning rate reducing effect. Derived synergistic effectivity (E s) values fall within the limits 0 < E s < 1 indicating a less than additive interaction.TGA/DTA analysis of oxalate/PA66 blends suggested that only zinc oxalate (ZnO x ) offers both possible flame retardant activity in terms of enhanced residue formation ≥500 °C, coupled with acceptable stability in molten PA66. When compounded with PA66, in the presence and absence of either aluminium diethyl phosphinate (AlPi)-based or selected polymeric bromine-containing flame retardants, LOI values increased in most PA66/ZnO x /flame retardant blends but UL94 test ratings were disappointingly low and more likely than not, “fails”. PA66/ZnO x blends with AlPi and AlPi/MPP gave poor plaques suggesting that thermal interactions were occurring during compounding.The bromine-containing blends had better processability and both TGA and cone calorimetric studies showed that the PA66/poly(pentabromobenzyl acrylate)/ZnO x sample not only yielded the highest residues in air and nitrogen at 500 and 580 °C, but also the lowest peak heat release rate value of 398 compared with 1276 kW/m2 for pure PA66. The derived E s value for this blend is 1.17 suggesting a small level of synergy between the zinc oxalate and poly(pentabromobenzyl acrylate) flame retardant. The possible role of zinc bromide is discussed.
Keywords: Metal oxalates; Cotton; Polyamide 6.6; Phosphorus; Bromine; Synergism;

Photocurable thiol-ene formulations have tendency to undergo premature dark polymerization leading to a reduced pot-life and therefore only limited applications can be envisaged with these systems. New stabilizers and stabilization systems were experimented through thermal stability and photoreactivity studies. The experimental results highlighted their superior stabilization efficiency regarding photocurable thiol-(meth)acrylate resins. A stabilization system composed of lauryl gallate and triphenylphosphite showed excellent stabilization efficiency with enhanced photoreactivity of the thiol-(meth)acrylate resin and preserved thermo-mechanical properties of the photocured resin. Beyond the scope of stabilization of the target thiol-ene systems, lauryl gallate and triphenylphosphite can be envisaged as efficient stabilizers for other polymers against light ageing thanks to their friendly chemical nature. Origins and existing solutions in the art as regard to this stability issue are also discussed.
Keywords: Photopolymers; Thiol-ene; Thiol-(meth)acrylates; Premature dark polymerization; Stabilization;

Kinetics of radiation-induced degradation of CF2- and CF-groups in poly(vinylidene fluoride): Model refinement by Alena Leonidovna Sidelnikova; Vladimir Petrovich Andreichuk; Leonid Abramovich Pesin; Sergey Evgenievich Evsyukov; Igor Vasil'evich Gribov; Natalia Anatol'evna Moskvina; Vadim L'vovich Kuznetsov (308-311).
XPS of partially crystalline PVDF film have been studied in the course of carbonization under Al Kα radiation. The long-term exposure of PVDF film and enhancement of the spectra resolution allowed further refinement of the previously proposed degradation model, which does not take into account practical impossibility of complete elimination of fluorine. Due to a random character of photon interactions with a polymer backbone, there is a possibility of the formation of isolated CF2 (CF) and CH2 (CH) groups that can never decay. The basic equation from the original model has been rewritten considering of formation of such groups. Kinetics of CF2 and CF groups elimination confirms that microscopic mechanism of their decay can be described by the second-order reaction.
Keywords: Polyvinylidene fluoride (PVDF); Radiative carbonization; X-ray photoelectron spectroscopy; Defluorination; Kinetics;

Hydrolytic degradation of monomer casting nylon in subcritical water by Wei Wang; Linghui Meng; Yudong Huang (312-317).
In contrast with the conventional physical methods, sub- and supercritical hydrolysis is not only a more environmentally friendly method to recycle the monomer casting nylon (MC nylon) wastes, but also a more feasible way to produce the corresponding monomer. In subcritical water, MC nylon was decomposed completely into water-soluble oligomers within 45 min at 345 °C and 9 MPa. Fourier transform infrared spectroscopy and X-ray diffraction were employed to characterize the chemical composition and crystalline form changes of the solid products obtained within 30 min of the degradation. Qualitative and quantitative analyses of liquid phase product were performed by liquid chromatography mass spectrometry and high performance liquid chromatography. The yield of the main degradation product ε-caprolactam largely depended on the hydrolysis temperature and reaction time. The maximum yield value reached 89.0% when the reaction time was 75 min. A hydrolytic degradation mechanism of MC nylon in subcritical water is proposed as well.
Keywords: Monomer casting nylon; Hydrolysis; Degradation; Subcritical water;

Reaction model describing antioxidant depletion in polyethylene–clay nanocomposites under thermal aging by Iftekhar Ahmad; Christopher Y. Li; Y. Grace Hsuan; Richard A. Cairncross (318-335).
Antioxidants are typically added to polyethylene to extend its durability, and recently clay nanoparticles have been blended into polyethylene to improve mechanical properties. However, the clay nanoparticles also accelerate the rate of antioxidant depletion in polyethylene. This paper uses a mathematical model to describe the underlying mechanisms of antioxidant (hindered-phenol) depletion and to predict experimentally-measured antioxidant profiles in polyethylene–clay nanocomposites. The mathematical model uses a reaction kinetic scheme that includes free radical initiation and propagation reactions, antioxidant stabilization reactions and free radical termination reactions. In the model, alkyl free radicals oxidize rapidly. The role of antioxidants is to stabilize the oxidized free radicals to hydroperoxides, and interrupt propagation reactions. However, in nanocomposites, continuous depletion of antioxidant is caused by the clay acting as a catalyst to decompose hydroperoxides and regenerate alkyl free radicals. This cyclic hydroperoxide generation and decomposition leads to much faster antioxidant depletion in polyethylene nanocomposites. Phenoxyl radicals of antioxidants generated by stabilization reactions contribute to terminate polymeric free radicals and limit their accumulation. Predictions of antioxidant depletion are compared to experimental results for accelerated aging of polyethylene and nanocomposite samples.
Keywords: Antioxidant depletion; Polyethylene–clay nanocomposite; Kinetic model; Thermo-oxidative degradation; Hydroperoxide decomposition; Polymer degradation;

Macromolecular antioxidants via thiol-ene polyaddition and their synergistic effects by Stephan Beer; Ian Teasdale; Oliver Brueggemann (336-343).
Photochemically initiated thiol-ene addition chemistry was used to prepare an aliphatic polythioether, which was applied as a thiosynergist in combination with macromolecular phenolic antioxidants for the thermal oxidative stabilization of polyolefins. Blends with polypropylene showed an extraordinary oxidative stability due to synergistic effects of the polythioether. Furthermore, the synthesis of an “all-in-one” primary and secondary macromolecular antioxidant was reported, with phenolic antioxidants attached to a polythioether backbone. Two different synthetic approaches to incorporate the thioether and the phenolic antioxidant functions into a single macromolecule were investigated, with a post-polymerization approach proving to be superior to a macromonomer approach. The excellent results in OIT measurements in comparison to commercial antioxidants, in particular of the polythioether blends, coupled with their high molecular weights designed to inhibit leaching, makes these macromolecular antioxidants interesting additives for the long-term stabilization of polyolefins in challenging environments.
Keywords: Thiol-ene addition; Antioxidant; Sterically hindered phenol; Thiosynergist; Immobilization; Polypropylene;

Degradation of chitosan by sonication in very-low-concentration acetic acid by Emma Savitri; Sri Rachmania Juliastuti; Anitarakhmi Handaratri; Sumarno; Achmad Roesyadi (344-352).
Chitosan is a linear copolymer composed of (1 → 4)–linked 2-acetamido-2-deoxy-β-D-glucan (GlcNAc) and 2-amino-2-deoxy-β-D-glucan (GlcN) units in varying proportions, having a high molecular weight and strong intra- and intermolecular hydrogen bondings. Sonication has become an alternative for degrading chitosan into low-molecular-weight chitosan (LMWC), chitosan oligomers and glucosamine. In this study, chitosan was treated with sonication at 40 °C and 60 °C for 30 min and 120 min with various acetic acid concentrations (0.2% v/v–1% v/v); the very-low-concentration acid solution functioned both as a solvent and catalyst. After sonication, the samples were tested for changes in molecular weight, water soluble proportion of chitosan (chitosan oligomers and glucosamine), degree of deacetylation, degree of crystallinity, and morphology. The soluble and insoluble product yields at low concentration (0.5% v/v) at 40 and 60 °C were 33.66–39.37 % and 32.43–34.26%, respectively. The main product was 5-hydroxy methyl furfural with composition 92.16–99.43%. At high concentrations (1% v/v), the soluble product and insoluble yields were 43.72–49.74% and 43.1–50.26%, respectively. The main product was glucosamine with composition 77.75–93.16% of glucosamine. There were changes in the morphology and crystallinity of the degraded chitosan, but no change in the chemical structure. The crystallinity had a tendency to increase. The degree of deacetylation tended to decrease due to the glucosamine breakage.
Keywords: Chitosan; Sonication; Acetic acid; Oligomers; Glucosamine;

Influence of melt processing conditions on poly(lactic acid) degradation: Molar mass distribution and crystallization by Pierre Erwan Le Marec; Laurent Ferry; Jean-Christophe Quantin; Jean-Charles Bénézet; Frédéric Bonfils; Stéphane Guilbert; Anne Bergeret (353-363).
The degradation of poly(lactic acid) (PLA) during thermal–mechanical processing was studied and the influence of processing conditions on degradation rate was determined by size exclusion chromatography coupled with multi-angle light scattering (SEC–MALS). A two-parameter model accounting for both chain scission and recombination processes was used to describe the experimentally observed molar mass distribution. The degradation and recombination rate constants were determined for undried and dried PLA. It was highlighted that the effect of processing temperature (in the 170–210 °C range), processing time (until 30 min) and shear rate (rotor speed varying from 0 to 150 rpm) on molar mass reduction can be relatively well simulated insofar as self-heating related to the mechanical energy conversion into heat was taken into account.The influence of melt processing on the thermal behaviour of PLA was also investigated using temperature modulated differential scanning calorimetry (TMDSC). It was evidenced that the molar mass reduction affects the crystallizability of PLA. Cold crystallization temperature progressively decreases with decreasing molar mass and the metastable α' phase is formed in place of the stable α phase. The α′ phase can be partially converted into α form during melting giving rise to a double-melting peak. The two peaks can be separated using reversing and non-reversing signals confirming that recrystallization of the α′ form occurs.
Keywords: Poly(lactic acid) (PLA); Melt processing; Thermal degradation; Molar mass; Crystallization; Simulation;

Cu- and Zn-acetate-containing ionic liquids as catalysts for the glycolysis of poly(ethylene terephthalate) by A.M. Al-Sabagh; F.Z. Yehia; A.M.F. Eissa; M.E. Moustafa; Gh. Eshaq; A.M. Rabie; A.E. ElMetwally (364-377).
The glycolysis of polyethylene terephthalate (PET) was studied using 1-butyl-3-methylimidazolium acetate-promoted copper acetate (Cu(OAc)2-[Bmim][OAc]) and 1-Butyl-3-methylimidazolium acetate-promoted zinc acetate (Zn(OAc)2-[Bmim][OAc]) as catalysts. The effects of temperature, time, ethylene glycol (EG) amount, PET amount and catalyst dosage on the glycolysis reaction were examined. Under the optimal conditions of 1.0 g of catalyst with 20 g of EG in the presence of 3.0 g of PET at 190 °C after 3 h of glycolysis, complete PET conversion was achieved using Cu(OAc)2-[Bmim][OAc] and Zn(OAc)2-[Bmim][OAc], and the yield of bis (2-hydroxyethyl) terephthalate (BHET) reached 53.95% and 45.6%, respectively. The ionic liquid could be reused up to 6 times with no apparent decrease in the PET conversion or BHET yield. The reaction mechanism was proposed. The reaction kinetics for Cu(OAc)2-[Bmim][OAc] and Zn(OAc)2-[Bmim][OAc] was first-order with an activation energy of 56.4 kJ mol−1 and 53.8 kJ mol−1, respectively.
Keywords: Glycolysis; Recycling; Polyethylene terephthalate; Degradation; Catalysis;

Study of the effect of atmospheric pressure air dielectric barrier discharge on nylon 6,6 foils by Anna Kuzminova; Artem Shelemin; Ondřej Kylián; Andrei Choukourov; Helena Valentová; Ivan Krakovský; Jan Nedbal; Danka Slavínská; Hynek Biederman (378-388).
Nylon 6,6 foils have been treated by an atmospheric pressure air dielectric barrier discharge. The action of plasma on nylon foils was determined by means of a wide range of techniques that enabled us to study changes in their surface as well as bulk properties. The plasma treatment was found to cause significant changes in morphology, surface chemical composition and wettability of the foils depending on the treatment time. On the other hand, optical, thermal and mechanical properties remained unaffected by plasma treatment even for prolonged treatment duration. In addition, independence of dielectric properties of nylon 6,6 foils of the plasma treatment was observed except for the high temperature region. These results clearly show that air atmospheric plasma treatment is suitable for applications in which modification of surface properties of nylon without alteration of their bulk properties is required.
Keywords: Nylon 6,6; Dielectric barrier discharge air plasma; Surface modification; Plasma treatment;

The degradation of poly(ethylene terephthalate) (PET) was investigated through a weathering test by using a xenon weather meter. The degraded structure was evaluated by means of gel permeation chromatography (GPC), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and positron annihilation lifetime spectroscopy (PALS). The GPC results indicated a decrease of number average molecular weight and a broadening of polydispersity with the degradation of PET, probably due to chain scission and some networking reactions. The DSC results indicated that the crystallinity index was changed through the weathering test. However, the change of crystallinity was poorly correlated with the progress of degradation. In the Tan δ measurement by DMA, suppression of molecular mobility during the degradation was implied by the increase in T g with increasing exposure time. The PALS results revealed that the free-volume hole size decreased with increasing exposure time. The decrease in the free-volume hole size can be attributed to the interaction between functional groups produced by hydrolysis or photochemical chain scission. The change of properties and structure in the amorphous part of PET was found to be correlated with the progress of the degradation in the weathering test.
Keywords: Poly(ethylene terephthalate); Weatherability; Amorphous; Dynamic mechanical analysis; Positron annihilation; Free volume;

Catalytic pyrolysis and flame retardancy of epoxy resins with solid acid boron phosphate by You Zhou; Jie Feng; Hui Peng; Hongqiang Qu; Jianwei Hao (395-404).
A solid acid boron phosphate (BP) has been prepared and characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The catalytic effects of BP on pyrolysis and flame retardancy of epoxy resins (EP) were studied by various methods. Transmission electron microscopy images suggested that BP was uniformly dispersed into the EP matrix. Differential scanning calorimetry illustrated that loading of BP could slightly reduce the glass transition temperature of EP. Thermogravimetric analysis and Fourier-transform infrared spectrometry indicated that BP catalyzed EP to pyrolysis at a lower temperature, leading to a reduction of flammable gas release and an increased residue yield. Limiting oxygen index (LOI) and UL 94 data showed that when the BP loading was increased, the LOI value increased accordingly. In addition, the UL 94 level was improved from no rating to a V-1 rating. In cone calorimeter measurements, a compact intumescent “honeycomb-like” char layer was found for the EP/BP composites, which led to considerable decreases in the maximum peak of heat release rate and total heat released. A possible catalytic flame retardant mechanism for the EP/BP composites is proposed.
Keywords: Boron phosphate; Epoxy resins; Pyrolysis; Flame retardancy; X-ray photoelectron spectroscopy;

Reactive UV-absorber and epoxy functionalized soybean oil for enhanced UV-protection of clear coated wood by Sara K. Olsson; Mats Johansson; Mats Westin; Emma Östmark (405-414).
The present work investigates the photostabilising effect of a pretreatment consisting of 2-hydroxy-4(2,3-epoxypropoxy)-benzophenone (HEPBP) and epoxy functionalized soybean oil (ESBO), reacted on to Scots pine veneers coated with two different acrylic top coats. Two different pretreatment procedures were used, varying in reaction time and temperature. Results from FTIR and SEC analysis indicate that a large amount of reactant was present on the veneers after treatment with either of the two reaction procedures. Furthermore, coating of the pretreated surfaces was possible and the pretreatment does not seem to affect the adhesion between the coating and the wood substrate. Both accelerated ageing and natural exposure was used to study the resistance to photodegradation, and the results were analysed using colour measurements, FTIR and SEM. These analyses all show that 1400 h of accelerated ageing degrades neither the wood nor the coating to any larger extent. However, after 4000 h of UV exposure some signs of degradation are visible but to a lesser extent for pretreated samples. For the samples exposed to natural weathering during 14 months the performance was good in terms of photostabilisation, however all samples suffer from mould to different extents. Pretreated samples show smaller and more evenly distributed areas of mould compared to the references, which show slightly more mould. The combined coating/pretreatment system is thus assumed to have an effect in terms of photostabilization of the coated wood.
Keywords: UV-protection; Epoxy functional vegetable oil; Soybean oil; 2-Hydroxy-4(2,3-epoxypropoxy)-benzophenone; Photodegradation; Weathering;

A molecular based kinetic study on the thermal decomposition of poly-α-methyl styrene by Jia Fu; Weiguo Sun; Yonghong Jiang; Qunchao Fan; Yi Zhang; Zhanwen Zhang (415-421).
Solid polymer thermal decomposition involves complex physical and chemical processes that are closely related to the microscopic molecular information (chemical structure, physical configuration, etc.). However, some important molecular information such as molecular weight is seldom involved in previous solid thermal decomposition studies due to the complexity of solid polymer itself. This work proposes a kinetic equation to study solid polymer thermal decomposition in which the influence of molecular weight to the decomposition is included based on an independent identical particle (IIP) model. Applications of this equation to the thermal decomposition of solid poly-α-methyl styrene (PαMS) show that: 1) there is good agreement between experimental and theoretical thermal decomposition rates; 2) molecular weight can affect not only the activation energy but also the pre-exponential factor of the thermal decomposition kinetic equation; 3) the higher the molecular weight is, the faster the PαMS decomposes in the main decomposition temperature range.
Keywords: Thermal decomposition; Polymer; Solid; Molecular weight; Activation energy;

Depth-resolved infrared microscopy and UV-VIS spectroscopy analysis of an artificially degraded polyester-urethane clearcoat by Koen N.S. Adema; Hesam Makki; Elias A.J.F. Peters; Jozua Laven; Leendert G.J. van der Ven; Rolf A.T.M. van Benthem; Gijsbertus de With (422-434).
Polyester-urethane resins are important candidates for high performance, outdoor coating applications. Despite their relevance, quantitative information regarding the photodegradation of these materials is scarcely available. In the present study, a model polyester-urethane clearcoat without additives is artificially degraded and the changes in optical properties and chemical composition are studied by UV-VIS spectroscopy and FTIR-ATR microscopy, respectively. The change of the optical properties throughout the coating thickness is quantified and interpreted using a newly developed optical model. Chemical changes are quantified in a depth-resolved manner by combining FTIR-ATR microscopy with optical profilometry in order to visualise the time evolution of compositional gradients during photodegradation by accurate assignment of the correct depth position to all recorded ATR spectra. The rate of change for the concentration of several chemical entities in the model polyester-urethane was found to become constant after the initial stage of weathering. The loss of urethane crosslinks in the coating occurs faster and to a much larger extent as compared to ester bond scission. Results from the optical and the chemical characterisation are combined to propose a kinetic model for ester bond photolysis that provides an estimate of the quantum efficiency of this process.
Keywords: Photodegradation; Polyester-urethane; UV-VIS spectroscopy; FTIR-ATR microscopy;

Studying the effect of the chloral group on the thermal and physical properties of aromatic cyanate esters by Ian Hamerton; Brendan J. Howlin; Lyndsey Mooring; Corinne Stone; Martin Swan; Scott Thompson (435-446).
Two cyanate ester monomers: 2,2-bis(4-cyanatophenyl)propane (1) and l,l-dichloro-2,2-(4-cyanatophenyl)ethylidene (2) are formulated with copper(II) acetylacetonate (200 ppm) in dodecylphenol (1% w/v active copper suspension) and cured (2 K/min to 150 °C + 1 h; 2 K/min to 200 °C + 3 h) followed by a post cure (2 K/min to 260 °C + 1 h). The polymerisation enthalpy for the thermal polymerisation of monomer (2) was recorded as 87.6 ± 0.75 kJ/mol. OCN (75.0 ± 0.80 kJ/mol. OCN following catalysis) and 99.4 ± 1.86 kJ/mol. OCN, 85.8 ± 4.03 kJ/mol. OCN following catalysis for (1). Formulated monomers show little advancement in cure during storage at a several temperatures (ambient, −5 °C and −20 °C) over a period of 2 months. TGA measurements conducted on cured ‘puck’ sample3s reveal char yields of 38% at 800 °C in the case of (1) and 54% for (2). Pyrolysis-GC shows only minor similarities in the species detected implying that the two polymers undergo significantly different degradation pathways under the analysis conditions, but the low incidence of polynuclear aromatics present (aside from substituted fluorenes, biphenyls and anthracenes) is probably due to the rapidity of heating a short residence times involved.
Keywords: Cyanate esters; Chloral polymers; Thermomechanical properties; Thermal stability;

Disulfides – Effective radical generators for flame retardancy of polypropylene by Weronika Pawelec; Anton Holappa; Teija Tirri; Melanie Aubert; Holger Hoppe; Rudolf Pfaendner; Carl-Eric Wilén (447-456).
The potential of thirteen aliphatic, aromatic, thiuram and heterocyclic substituted organic disulfide derivatives of the general formula R–S–S–R′ as a new group of halogen-free flame retardants (FR) for polypropylene films have been investigated. According to DIN 4102-1 standard ignitibility test, for the first time it has been demonstrated that many of the disulfides alone can effectively provide flame retardancy and self-extinguishing properties to polypropylene (PP) films at already very low concentrations of 0.5 wt%. In an effort to elucidate the mechanism of the thermal decomposition of disulfide derivatives the fragmentation patterns of the evolved gases from a thermogravimetric analyzer (TGA) have been analyzed by simultaneous mass spectrometry (MS) and Fourier transform infrared spectrometry (FTIR). The main decomposition products initiated by homolytic scission of the S–S bond and/or scission of the C–S bond were identified as thiols, aliphatic and aromatic hydrocarbons, isothiocyanates (depending on the disulfide structures) with further evolution of elemental sulfur and sulfur dioxide at temperatures of above 300 °C and 450 °C, respectively. Based on this preliminary study, we have shown that disulfides represented by e.g. diphenyl disulfide (1), 5,5′-dithiobis(2-nitrobenzoic acid) (2), bis(1-phenyl-1H-tetrazol-5yl)-disulfide (4), 2-bisbenzothiazole-2,2′-disulfide (6) and N,N-dithiobis-(phtalimide) (10) constitute a new halogen-free family of additives for flame retarding of polypropylene.
Keywords: Disulfide; Radical generator; Flame retardant; Polymer additive; Polypropylene;

Long term aging of LLDPE based multi-layer film by exposure to light hydrocarbons by Moshe Rabaev; Nir Goldin; Konstantin Tartakovsky; Itamar Tzadok; Udi Akiva; Roni Shneck; Moshe Gottlieb (457-463).
This study focuses on the stability of a polymeric Linear Low Density Polyethylene/Polyamide/Linear Low Density Polyethylene multi-layered container during long-term aging by exposure to light hydrocarbons in aviation gasoline. The containers examined and tested for this work were stored and used for different service periods, the longest of which is 10 years. During the containers' service periods, the inner LLDPE layer is exposed to avgas (aviation gasoline), and the outer LLDPE layer – to air. The aging process caused by the film interaction with avgas was examined by a variety of methods. Pb line-scan and IR spectroscopy show no evidence for the presence of small organic carbohydrate molecules originating from the avgas in the LLDPE. The viscoelastic and thermo-mechanical properties of the material were not significantly changed after 10 years. Nevertheless, DSC-OIT analysis shows a remarkable rise in oxidation rate as samples get older, presumably, as a result of antioxidants leaching out or being used up. The SEM results show the polymer to be much more prone to cracking, indicating a rise in crystallinity, as further substantiated by the results from DSC 1st heating cycle enthalpy evaluation. The 2nd DSC heating cycle results, which show no differences between samples, indicate the difference seen in the 1st heating cycle is affected by intermolecular rearrangements. Macro-mechanical properties show a remarkable stability for at least a decade, negating the aging phenomena discussed. Polyamide, as the load baring layer in the film, is probably responsible for the dampening seen in these results. In years to come, apparent oxidation will begin – most prominently in the outer layer – but probably would not compromise the structural strength of the bag, as both polyethylene layers are not the main load bearing layers.
Keywords: Polyethylene; Aging; LLDPE; Polyamide;

Hygrothermal aging effects on fatigue of glass fiber/polydicyclopentadiene composites by Yinghui Hu; Augustus W. Lang; Xiaochen Li; Steven R. Nutt (464-472).
We investigated the effects of hygrothermal aging on the tension–tension fatigue behavior of unidirectional (UD) glass/polydicyclopentadiene (pDCPD) composites. Samples were immersed in deionized (DI) water and salt water, and glass/epoxy composites were used as a benchmark for comparison. Composites of pDCPD showed less water uptake and superior fatigue performance compared to similarly aged epoxy composites, a distinction attributed to the intrinsic hydrophobicity of the pDCPD resin. Superior fiber-matrix interface adhesion in pDCPD composites accounted for the greater strength retention after aging. Degradation of fiber and interface were coupled but not synchronous: glass fiber degradation was determined by aging time, while interface degradation depended primarily on moisture level. Salt water influenced the amount of water absorption, but no salt water corrosion was observed for either composite.
Keywords: Polymer-matrix composites (PMCs); Environmental degradation; Fatigue; Acoustic emission;

In vitro degradation study of novel HEC/PVA/collagen nanofibrous scaffold for skin tissue engineering applications by Farah Hanani Zulkifli; Fathima Shahitha Jahir Hussain; Mohammad Syaiful Bahari Abdull Rasad; Mashitah Mohd Yusoff (473-481).
The aim of this study was focused on the degradation behavior of electrospun (hydroxyethyl cellulose/poly(vinyl) alcohol) HEC/PVA and HEC/PVA/collagen nanofibrous scaffolds, as a potential substrates for skin tissue engineering in two biologically related media: phosphate buffered solution (PBS) and Dulbecco's modified Eagle's medium (DMEM) for 12 weeks incubation period. The scaffolds were characterized at different degradation times by a series of analysis including pH changes of solutions, weight loss, swelling ratio, SEM, ATR-FTIR, DSC, TGA and mechanical properties. The results indicated that HEC/PVA/collagen scaffolds were exhibited slower degradation rate in both medium as compared to HEC/PVA blend nanofibers. All fibers displayed uneven and rough surfaces towards the final week of incubation in both PBS and DMEM solution. As degradation time increased, there were little changes in the chemical structure as determined by FTIR spectra while thermal studies revealed that the melting temperatures and crystallinity of scaffolds were slightly shifted to a lower value. Both HEC/PVA and HEC/PVA/collagen fibers showed significant decrease in Young's modulus and tensile stress over 12 weeks degradation. These results show that these nanofibrous scaffold demonstrate degradation behavior that meets the requirement as potential degradable biomaterials for dermal replacement.
Keywords: In vitro degradation; Hydroxyethyl cellulose; Collagen; Nanofibers scaffold; Tissue engineering;

Catalytic and thermal pyrolysis of polycarbonate in a fixed-bed reactor: The effect of catalysts on products yields and composition by E.V. Antonakou; K.G. Kalogiannis; S.D. Stefanidis; S.A. Karakoulia; K.S. Triantafyllidis; A.A. Lappas; D.S. Achilias (482-491).
A meaningful and advanced method concerning the management of waste electrical and electronic equipment (WEEE) becomes a necessity, mainly due to their increased production, applications and their short life. Thermal methods have been an attractive option and for this reason the investigation of pyrolysis and catalytic pyrolysis as a potential method for the recycling of polycarbonate (PC) based plastics has been the aim of the current study. Nine different catalysts with variations in properties (such as porosity and acidity/basicity) were introduced in a bench scale pyrolysis system together with the polycarbonate polymeric material and the pyrolysis fractions were collected and analyzed. The liquid product consisted mainly of phenols and substituted phenols as well as the original monomer and, due to the commercial value of these products in the chemical industry, it is expected to enhance the economic viability of the process. Results showed a reduction in the degradation temperature in the presence of all catalytic materials, depending on the pore characteristics and the acidic nature of the solid. It seems that in the presence of the basic catalysts, PC degradation leads to lower molecular weight compounds and high phenolic fractions in the liquid produced. In terms of reduction in the production of the monomer, pore size rather than acidity appears to be the determining factor.
Keywords: Polycarbonate; Pyrolysis; Zeolites; Catalysts; Phenols;

The present study investigates the degradation of poly(acrylic acid) in aqueous solution by a photo-Fenton-like process. Batch experiments are carried out to model and optimize the process. The effects of the initial concentration of poly(acrylic acid), the initial concentration of Fe3+, and the H2O2 dosage as independent variables on the total organic carbon (TOC) removal as the response function are studied using response surface methodology (RSM). The significance of the independent variables and their interactions are tested by means of analysis of variance (ANOVA) with 95% confidence level. The statistical analysis of the results indicated satisfactory prediction of the system behavior by the developed model. The optimum operating conditions to achieve maximum TOC removal are also determined. The model prediction for maximum TOC removal is compared to the experimental result at optimal operating conditions. A good agreement between the model prediction and experimental results confirms the reliability of the developed model.
Keywords: Poly(acrylic acid); Photo-Fenton-like; TOC removal; RSM; Statistical analysis; Process optimization;

Analytical evaluation of the performance of stabilization systems for polyolefinic materials. Part I: Interactions between hindered amine light stabilizers and phenolic antioxidants by Susanne Beißmann; Michael Reisinger; Klemens Grabmayer; Gernot Wallner; David Nitsche; Wolfgang Buchberger (498-508).
Degradation pathways and interactions between the phenolic antioxidant Irganox 1330 and three commercially used hindered amine light stabilizers (HALS) were successfully studied by accelerated aging of model formulations in the polymer-mimicking solvent squalane. Methods based on high-performance liquid chromatography hyphenated with mass spectrometric detection (HPLC-MS) were developed for structural elucidation of transformation products and monitoring of interactions between the two chemical groups. The developed method was able to differentiate and chromatographically separate transformation products originating from the HALS including the active aminoxyl radicals. The investigations showed a strong antagonism between HALS and phenols, leading to useless consumption of both stabilizer groups, whereby tertiary amines showed less effect compared to secondary HALS. By monitoring the degradation behavior of unstabilized squalane it was possible to perform a rating of stabilization efficiencies of the different systems.
Keywords: HALS; Phenolic antioxidants; Antagonism; Degradation; Accelerated aging; Model formulation;

In the present study, the applicability of high-performance liquid chromatography hyphenated with highly sophisticated mass spectrometric detection (HPLC-MS) for analysis of hindered amine light stabilizers (HALS), thiosynergists and their conversion products is demonstrated. Degradation pathways as well as interactions between these stabilizer groups were successfully studied by analytical evaluation of model formulations after accelerated aging in the polymer-mimicking solvent squalane. Binary mixtures including HALS and thiosynergist as well as three component systems additionally including a phenolic antioxidant were investigated. Results showed that transformation pathways of HALS are highly influenced by the presence of sulfur-containing compounds and no aminoxyl radicals (typical reactive intermediates of HALS) were observed in these mixtures. To get an understanding of the effect of this altered stabilization mechanism on the protection of the polymer, rating of stabilization efficacies was performed by comparing the amount of degradation products derived from squalane using different formulations.
Keywords: HALS; Thiosynergists; Phenolic antioxidants; Protection efficacy; Degradation pathway; Accelerated aging;

Forensic engineering of advanced polymeric materials – Part II: The effect of the solvent-free non-woven fabrics formation method on the release rate of lactic and glycolic acids from the tin-free poly(lactide-co-glycolide) nonwovens by Wanda Sikorska; Grazyna Adamus; Piotr Dobrzynski; Marcin Libera; Piotr Rychter; Izabella Krucinska; Agnieszka Komisarczyk; Mariana Cristea; Marek Kowalczuk (518-528).
We report the forensic engineering study on the non-woven fabrics made from poly(lactide-co-glycolide), PLGA, with low toxicity. The comprehensive degradation investigations were conducted under abiotic conditions. The extent of degradation was monitored by weight loss, composition and molar mass changes of the copolymer and by macro- and microscopic observations of the sample surfaces. The structure of the degradation products was evaluated at the molecular level by electrospray ionization mass spectrometry and high-performance liquid chromatography analysis. The degradation process takes place predominantly by the bulk erosion mechanism and rate of release of lactic and glycolic acids from the non-woven fabrics is dependent on their formation method. Described solvent-free formation method of nonwovens from the tin-free PLGA results in biomaterials with higher biocompatibility, what is particularly important for their applications. Moreover, the continuous release of lactic and glycolic acids from the PLGA biomaterials studied allows their gradual removal via biochemical processes and prevents local acidification of the body.
Keywords: Poly(lactide-co-glycolide); PLGA; Nonwovens; Biodegradable polymers; Hydrolytic degradation; HPLC-DAD analysis;

Crystallization behaviors of poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate]/poly(ethylene glycol) graft TEMPO-oxidized cellulose nanofiber blends by Jiaqi Zhang; Shuji Fujizawa; Akira Isogai; Takaaki Hikima; Masaki Takata; Tadahisa Iwata (529-536).
To accelerate the crystallization rate of poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate] [P(3HB-co-4HB)] that is a microbial and biodegradable polyester, poly(ethylene glycol) graft TEMPO-oxidized cellulose nanofiber (PEG-TOCN) was blended as a nucleating agent. The PEG was only blended and confirmed the effect on the difference between PEG-TOCN and PEG in all samples. The non-isothermal crystallization and isothermal crystallization behaviors of P(3HB-co-4HB) with three kinds of different 4HB contents blended with PEG-TOCN or PEG were investigated by differential scanning calorimeter, wide-angle X-ray diffraction, polarizing microscope and tensile test. The crystallization half time (t 1/2 ) was drastically decreased by blended with PEG-TOCN, indicating that the crystallization rate was accelerated in all cases. The POM images showed that the PEG-TOCN worked effectively to increase both the growth rate and amounts of spherulites of P(3HB-co-4HB). In addition, the crystallinity of PEG-TOCN blending samples was higher than that of non-blended samples in all cases.
Keywords: P(3HB-co-4HB); PEG-TOCN; Crystallization behavior; Crystallization half-time; Nucleating agent;