Polymer Degradation and Stability (v.130, #C)
Editorial Board (IFC).
Kinetics and mechanism of the thermal degradation of biopolymers chitin and chitosan using thermogravimetric analysis by Hamou Moussout; Hammou Ahlafi; Mustapha Aazza; Mohamed Bourakhouadar (1-9).
In this work, the kinetics of thermal degradation of chitin and chitosan polymers were investigated by means of Fourier Transform Infrared Spectroscopy and thermogravimetric analyses in air atmosphere, under dynamic conditions in the range of 298–873 K. The kinetic parameters, such as the apparent activation energy (Ea) and pre-exponential factor (A) were determined using Ozawa–Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS) isoconversional methods. The experimental data were found, in the range of conversion fraction 0.1 < α <0.8, to be well described by the modified catalytic Sestak–Berggren (SB) model adapting the conversion function, f(α) = cα m (1−α) n with the adjusted values of m, n and c. It was found that the simulated curves issued from the model best fit those issued from the experimental data, indicating the same scission mechanism for the degradation of chitin and chitosan. It was found that the average value of Ea = 125 kJ/mol used in the simulated curves of chitin, Y (α) and Z (α), is comparable to those calculated by KAS and OFW, while for chitosan, it represents the mean value (Ea = 169 kJ/mol) between the values of Ea calculated by KAS (Ea = 191.61 kJ/mol) and OFW (Ea = 146.50 kJ/mol) methods.
Keywords: Chitin; Chitosan; Thermal degradation; Kinetic model;
Biodegradation of bicomponent PCL/gelatin and PCL/collagen nanofibers electrospun from alternative solvent system by J. Dulnik; P. Denis; P. Sajkiewicz; D. Kołbuk; E. Choińska (10-21).
Bicomponent polycaprolactone/gelatin and polycaprolactone/collagen nanofibers formed by electrospinning using various solvents were subjected to biodegradation and compared. Hexafluoroisopropanol (HFIP) was used as a reference solvent, while the second, alternative solvent system was the mixture of acetic acid (AA) with formic acid (FA). Biodegradation of investigated materials was manifested mainly by the gelatin leaching, including collagen which is indeed denaturated to gelatin during electrospinning, leading to nanofibers erosion. There was no molecular degradation of PCL during 90 days of biodegradation procedure as deduced from no change in the elongation stress at break. The rate of biopolymer leaching was very fast from all materials during the first 24 h of biodegradation, being related to surface leaching, followed by a slower rate leaching from deeper material layers. Mass measurements showed much faster biopolymer leaching from nanofibers electrospun from AA/FA than from HFIP because of strongly emulsive nature of the solution in the former case. Irrespective of the solvent used, the leaching rate increased with initial content of gelatin. The analysis of Young modulus during biodegradation indicated complex mechanism of changes, including biopolymer mass loss, increase of PCL crystallinity and partial gelatin renaturation.
Keywords: Bicomponent nanofibers; Biodegradation; Biopolymer;
Kinetics and mechanism of monomeric product from methanolysis of poly (3-hydroxybutyrate) catalyzed by acidic functionalized ionic liquids by Xiuyan Song; Hui Wang; Fusheng Liu; Shitao Yu (22-29).
Poly (3-hydroxybutyrate) (PHB) from an industrial manufacturer was depolymerized by methanol in the presence of acidic functionalized ionic liquids (ILs). It was demonstrated that 1-methyl-3-(3-sulfopropyl)-immidazolium hydrogen sulfate ([HSO3-pmim][HSO4]) exhibited higher catalytic activity than other acidic functionalized ILs and traditional acids such as H2SO4 and H3PO4. The main product of methanolysis was confirmed to be methyl 3-hydroxybutyrate monomer by FT-IR and 1H NMR. The influences of experimental parameters, such as the amount of catalyst, reaction temperature, methanolysis time, and dosage of methanol on the conversion of PHB and yield of methyl 3-hydroxybutyrate were investigated. The results showed that the reaction temperature was a critical factor for depolymerization of PHB. Under the optimum conditions of n(CH3OH):n(PHB) = 5:1, m(IL):m(PHB) = 0.03:1, reaction temperature 140 °C and time 3 h, the conversion of PHB and the yield of product were over 90% and 83%, respectively. The IL could be reused up to 6 times without apparent decrease in the conversion of PHB and yield of product. Kinetics of the reaction was also investigated, it was indicated that methanolysis of PHB catalyzed by acidic functionalized [HSO3-pmim][HSO4] was a first-order kinetic reaction with an activation energy of 16.02 kJ/mol. In addition, a detailed reaction mechanism of the methanolysis was proposed.
Keywords: Poly(3-hydroxybutyrate); Methanolysis; Acidic functionalized ionic liquid; Kinetics;
Lignin degradation and stability: Volatile Organic Compounds (VOCs) analysis throughout processing by Naïma Sallem-Idrissi; Caroline Vanderghem; Tiphanie Pacary; Aurore Richel; Damien P. Debecker; Jacques Devaux; Michel Sclavons (30-37).
This work investigates the Volatile Organic Compounds (VOCs) emissions during the processing of composite of polyamide 6 (PA) bio-filled with technical lignin. This is of prime interest as volatile phenolic structural monomers issued from lignin could penetrate the human organism and cause undesirable health damages. A special attention is given to the measurement of formaldehyde as it is known to be a human carcinogen. Lignin main identified emission consists of a high level of formaldehyde and a large amount of complex substituted phenol and benzene, all representative and constitutive of its structure. Regarding the PA alone, it has been found that the predominant VOC product is ε-caprolactam. When filling PA6 with lignin, the emitted VOCs associated to this filler are mainly produced during the extrusion while, only traces are detected during the injection process. Formaldehyde emission level is three times higher during the injection than during the extrusion. Phenols and some remaining reactants used during industrial cellulosic extraction process are identified. Regarding the value of the Short-Term Exposure Limit (STEL), suitable industrial process, safety and hygiene rules must be adopted.
Keywords: Lignin; Volatile organic compounds; Processing; Emissions; Extrusion; Injection;
Biodegradable polyester networks including hydrophilic groups favor BMSCs differentiation and can be eroded by macrophage action by Juan Manuel Fernández; Tamara Gisela Oberti; Line Vikingsson; José Luis Gómez Ribelles; Ana María Cortizo (38-46).
The aim of this study is to show that introducing a small fraction of hydrophilic groups into a hydrophobic polyester favor the macrophage activity by accelerating the degradation action in aqueous media. It is also seen that differentiation of MSCs cultured in monolayer towards bone in specific differentiation media is favored in these materials with respect to the corresponding pristine polyesters. Polymer networks based in polycarpolactone or poly(l-lactide) and containing a small fraction of poly(hydroxyethyl acrylate) have been synthesized. Degradation kinetics in vitro was monitored by mass loss and swelling capacity of the polymer network in good solvents, the later as representative of chain cleavage. Hydrolytic and enzymatic degradation is accelerated by the inclusion of poly(hydroxyethyl acrylate) blocks in the network. Macrophages were cultured on the surface of the network films, showing its capacity to erode the material surface but also to accelerate bulk degradation. Bone marrow mesenchymal stem cells were cultured in monolayer on the membranes in osteogenic media, showing an increase of specific markers expression in comparison to pristine polyesters.
Keywords: Polycaprolactone; Poly(l-lactide); Poly(hydroxyethyl acrylate); Macrophage erosion; Enzymatic degradation; Mesenchymal stem cells;
Effect of Wollastonite on the ablation resistance of EPDM based elastomeric heat shielding materials for solid rocket motors by Maurizio Natali; Marco Rallini; Josè Kenny; Luigi Torre (47-57).
EPDM/aramid fibers ablatives represent the state of the art Elastomeric Heat Shielding Materials (EHSMs) for Solid Rocket Motors (SRMs). Due to their mechanical properties and excellent thermal stability, aramid fibers or pulp constitute the common reinforcement of EPDM based formulations. Aramid fiber was introduced by NASA and space companies such as Orbital-ATK with the aim to replace asbestos. Space Shuttle’s reusable SRMs and many ICBMs employed Nitrile butadiene rubber (NBR) loaded with asbestos (ASNBR) as a primary internal case insulation; however, due to cancerogenicity of asbestos, NASA sought a replacement for many years, but this goal has been very challenging to achieve since the comprehensive performance of ASNBR was and is still difficult to match. Wollastonite can be considered the only non-hazardous mineral/inorganic filler able to partially replace asbestos. Wollastonite is a calcium inosilicate mineral (CaSiO3) and the shape of the filler is acicular. Our study wanted to evaluate Wollastonite as a possible replacement of aramid pulp in the production of EPDM based EHSMs for solid rocket motors. The heat capacity, thermal and dimensional stability, mechanical properties, and ablation resistance of the produced materials were studied and here reported.
Keywords: Ablative materials; Elastomeric heat shielding materials; Solid rocket motors; Thermal protection system;
Forecasting linear aliphatic copolyester degradation through modular block design by Veluska Arias; Peter Olsén; Karin Odelius; Anders Höglund; Ann-Christine Albertsson (58-67).
The development of efficient methods to predict the degradation of renewable polymeric materials is continuously sought in the field of polymer science. Herein, we present a modular build-up approach to create polyester-based materials with forecasted degradation rates based on the hydrolysis of the constituent polymer blocks. This involved the strategic combination of critical factors affecting polyester hydrolysis, i.e. hydrophobicity and degree of crystallinity. The starting point of this method was a toolbox of polymers with different hydrophobicities and degrees of crystallinity, as well as an understanding of their inherent differences in hydrolysis rate. Knowledge of the hydrolysis of each polymer block module enabled the prediction of the overall degradation behavior of the constructed copolymers. Taking advantage of the primary factors that affect polymer degradation, block copolymers could be independently designed to incorporate soft or rigid and faster or slower degradation properties. This approach generated a shift for how molecular design can be used to predict the degradation behavior of intended materials for different applications.Display Omitted
Keywords: Polyesters; Hydrolysis; Hydrophobicity; Crystallinity; Macromolecular engineering;
Synthesis of a novel macromolecular charring agent with free-radical quenching capability and its synergism in flame retardant polypropylene by Huali Xie; Xuejun Lai; Hongqiang Li; Xingrong Zeng (68-77).
Fabricating an effective synergism between the condensed phase (char-forming) and the gas phase (free-radical quenching) is recently considered to be a very promising way to prepare high-efficient intumescent flame retardants. In this work, a novel hindered amine phosphorous-nitrogen macromolecular charring agent (HAPN) with free-radical quenching capability was synthesized and characterized. Then it was combined with ammonium polyphosphate (APP) to flame-retard polypropylene (PP). The flame retardancy and thermal stability of PP/HAPN/APP mixtures were investigated by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimetric test (CCT) and thermogravimetric analysis (TGA). When the content of HAPN/APP was 25 wt%, PP/HAPN/APP could self-extinguish at 36 s after igniting in the oxygen concentration of 29.5% and achieve a UL-94 V-0 rating. Meanwhile, the peak heat release rate (PHRR), total heat release rate (THR), average heat release rate (AV-HRR) and average mass loss rate (AV-MLR) were significantly decreased. The flame retardant mechanism of HAPN/APP was explored and the results revealed that there was an effective synergism between the condensed phase and the gas phase during the combustion. In the condensed phase, HAPN could make PP involve into the char-forming reaction to promote the formation of compact and firm intumescent char layer. Simultaneously, the nitroxyl radical generated by HAPN could effectively restrain and even extinguish the flame in the gas phase by quenching the active free-radicals.
Keywords: Polypropylene; Intumescent flame retardant; Macromolecular charring agent; Free-radical quenching capability; Synergism;
Contrast effect on hydrolysis of poly(trimethylene carbonate) depending on accelerated species due to the hydrophilic oligo(ethylene glycol) units at side groups by Yoshiaki Haramiishi; Nalinthip Chanthaset; Kai Kan; Mitsuru Akashi; Hiroharu Ajiro (78-82).
Poly(trimethylene carbonate) (PTMC) is a biodegradable polymer which doesn’t generate any acidic organic compounds after hydrolysis, leading to good biocompatible properties and biomedical application. Poly(TMCM-MOE3OM) and poly(TMCE-MOE4OM), bearing oligo ethylene glycol (OEG) at the side chain of PTMC, were selected to investigate in vitro accelerating hydrolysis behaviors at pH = 7.4 in a phosphate-buffered solution (PBS) through the use of Lipase and NaOHaq. Their degradation behaviors were in contrast to that of PTMC, resulting in the fast degradation in NaOHaq. and the slow degradation by Lipase. The contrast in results of degradations are due to the side chain of hydrophilic OEG which should interact with degradation species.
Keywords: Trimethylene carbonate; Degradation; Oligo ethylene glycol;
Influence of temperature and stabilization on oxygen diffusion limited oxidation profiles of polyamide 6 by Pieter Gijsman; Weifu Dong; Adam Quintana; Mathew Celina (83-96).
The oxidative degradation behavior of polymers depends on a combination of chemical and physical factors, with oxygen diffusion being one of the most important, especially when the oxygen consumption rate is larger than its permeability.As a result of diffusion limited oxidation (DLO), at high temperatures the degradation rate of polyamide 6 (PA6) plaques is heterogeneous, with the polymer oxidizing much faster at the surface than in the bulk. Normalized carbonyl index (CI) and UV absorption – depth profiles were found to be mostly degradation time independent, implying equilibrium degradation conditions where oxygen permeability and reaction rates did not change significantly with degradation time. The experimental DLO profiles were described using a basic reactive-diffusion model based on Fickian oxygen diffusion and an oxidation rate being first order in local O2 concentration, as well as by applying an established DLO model based on the basic autoxidation mechanism. Analysis with the second model yielded the best estimation of high temperature oxygen permeability ( P O 2 ) data. It also showed some of the limitations in the data analysis when using a simple first order DLO model.It was shown that stabilizers have an influence on the oxidation - depth profiles. Better stabilization results in slower polymer oxidation and the oxidation – depth profiles are therefore less pronounced. At 170 °C it was observed that stabilized plaques (0.5 mm) in the center oxidize faster than unstabilized plaques, which is attributed to the complete consumption of oxygen in the outer layers for the unstabilized plaques. Oxidation rates of differently stabilized samples were also determined by applying the second DLO model.
Keywords: Polyamide 6; Copper; Irganox® 1098; Diffusion limited oxidation; Oxidation profiles; IR and UV-Spectroscopy; Mechanical properties;
Continuous flame-retardant actions of two phosphate esters with expandable graphite in rigid polyurethane foams by Wang Xi; Lijun Qian; Zhigang Huang; Yanfang Cao; Linjie Li (97-102).
The flame-retardant rigid polyurethane foams (RPUFs) with dimethyl methylphosphonate (DMMP)/[bis(2-hydroxyethyl)amino]-methyl-phosphonic acid dimethyl ester (BH)/expandable graphite (EG) were prepared by box foaming. The DMMP/BH/EG flame-retardant system with certain components ratio increased the LOI value, decreased the peak value of heat release rate, sustained the effective heat of combustion and total heat release in low level, and promote the formation of phosphorus-rich compact char layer comparing with DMMP/EG and BH/EG systems. The results imply that DMMP/BH/EG possessed the trinary synergistic flame-retardant effect. The results from thermogravimetric analysis (TGA) and TGA-gas chromatography-mass spectrometer (TGA-GC-MS) all confirmed that the trinary synergistic effect of DMMP/BH/EG was caused by the continuous release of DMMP/EG and BH/EG flame-retardant actions with increasing temperature. DMMP/EG and BH/EG in sequence worked in inhibiting flame and forming phosphorus-rich char layer, thus forming stable flame-retardant action on matrix and endowing RPUFs with the increased flame-retardant performance.
Keywords: Flame retardant; Polyurethane foams; EG; Phosphate ester;
Decrosslinking reaction kinetics of silane-crosslinked polyethylene in sub- and supercritical fluids by Bum Ki Baek; Yun Ho La; Albert S. Lee; Haksoo Han; Seong Hun Kim; Soon Man Hong; Chong Min Koo (103-108).
Supercritical methanol is a popular fluid as a supercritical medium for decrosslinking reaction of crosslinked polyethylene. However, due to its toxicity, a safe alternative medium is much to be desired. In this work, various sub- and supercritical fluids with different polarity characters were investigated to find a safe alternative medium for continuous decrosslinking of silane-crosslinked polyethylene (S-XLPE). Like methanol, all examined fluids, including ethanol, propanol, and water, exhibited first-order reaction kinetics regarding the gel content in the continuous decrosslinking process. The reaction rate constant values were observed as 2.806, 2.569, 2.383, and 2.130 min−1 in supercritical methanol, supercritical ethanol, supercritical 2-propanol, and subcritical water at 380 °C, respectively. As a non-toxic fluid with reaction kinetics very comparable to that of methanol, ethanol was found to be the best alternative medium for the continuous decrosslinking reaction of S-XLPE.
Keywords: Silane-crosslinked polyethylene; Supercritical fluids; Decrosslinking; Continuous process; Kinetics; Recycling;
The museum in a test tube – Adding a third dimension to the evaluation of the impact of volatile organic acids on paper by M. Becker; F. Meyer; M.-J. Jeong; K. Ahn; U. Henniges; A. Potthast (109-117).
Collections of art on paper, libraries and archives in general, are striving for optimal storage conditions for cultural heritage in their deposits and exhibition facilities. Therefore, properly estimating the risk of volatile organic compounds emitted from historic and recent storage materials on paper-based collections is of utmost importance. Applying an optimized static headspace gas chromatography and mass spectrometry approach combined with cellulose-specific analysis provides insight into the potential degradation effects and mechanisms acting on two different paper samples (Whatman No.1 and historic rag paper) used as degradation indicators. Acetic and formic acid, two powerful volatile organic acids, were quantified with differing amounts, depending on the type of historic storage material tested. Molar mass and carbonyl group content were used to monitor cellulose degradation of the indicator papers. Combining these results in 3D plots helps to visualize synergies that evolve from mutual emission of acetic and formic acids. In addition, choosing between the two paper-based degradation indicators helps to evaluate different phenomena: Whatman No.1 reacts toward acid hydrolysis and is more sensitive, while rag paper helps to evaluate buffering phenomena as occurring in original materials.Display Omitted
Keywords: Acetic acid; Formic acid; Paper degradation; Static headspace gas chromatography; Volatile organic compounds (VOC); Cellulose analysis;
A comparative study on Poly(ε-caprolactone) film degradation at extreme pH values by G. Patricia Sailema-Palate; A. Vidaurre; A.J. Campillo-Fernández; I. Castilla-Cortázar (118-125).
The present paper studies the effect of pH on hydrolytic degradation of Poly(ε-caprolactone) (PCL) Degradation of the films was performed at 37 °C in 2.5 M NaOH solution (pH 13) and 2.5 M HCl solution (pH 1). Weight loss, degree of swelling, molecular weight, and calorimetric and mechanical properties were obtained as a function of degradation time. Morphological changes in the samples were carefully studied through electron microscopy. At the start of the process the degradation rate of PCL films at pH 13 was faster than at pH 1. In the latter case, there was an induction period of around 300 h with no changes in weight loss or swelling rate, but there were drastic changes in molecular weight and crystallinity. The changes in some properties throughout the degradation period, such as crystallinity, molecular weight and Young’s modulus were lower in degradations at higher pH, highlighting differences in the degradation mechanism of alkaline and acid hydrolysis. Along with visual inspection of the degraded samples, this suggests a surface degradation at pH 13, whereas bulk degradation may occur at pH 1.
Keywords: PCL; Hydrolytic degradation; pH; Hydrolysis;
New genre of antioxidants from renewable natural resources: Synthesis and characterisation of rosemary plant-derived antioxidants and their performance in polyolefins by K. Doudin; S. Al-Malaika; H.H. Sheena; V. Tverezovskiy; P. Fowler (126-134).
Several ester derivatives of rosmarinic acid (rosmarinates) were synthesised, characterised (1D and 2D NMR, UV and FTIR spectroscopy) and tested for their potential use as antioxidants derived from a renewable natural resource. The intrinsic free radical scavenging activity of the rosmarinates was assessed, initially using a modified DPPH (2, 2-diphenyl-1-picrylhydrazyl radical) method, and found to be higher than that of commercial synthetic hindered phenol antioxidants Irganox 1076 and Irganox 1010. The thermal stabilising performance of the rosmarinates in polyethylene (PE) and polypropylene (PP) was subsequently examined and compared to that of samples prepared similarly but in the presence of Irganox 1076 (in PE) and Irganox 1010 (in PP) which are typically used for polyolefin stabilisation in industrial practice. The melt stability and the long-term thermo-oxidative stability (LTTS) of processed polymers containing the antioxidants were assessed by measuring the melt flow index (MFI), melt viscosity, oxidation induction time (OIT) and long-term (accelerated) thermal ageing performance. The results show that both the melt and the thermo-oxidative stabilisation afforded by the rosmarinates, and in particular the stearyl derivative, in both PE and PP, are superior to those of Irganox 1076 and Irganox 1010, hence their potential as effective sustainable bio-based antioxidants for polymers.The rosmarinic acid used for the synthesis of the rosmarinates esters in this study was obtained from commercial rosemary extracts (AquaROX80). Furthermore, a large number of different strains of UK-grown rosemary plants (Rosmarinum officinalis) were also extracted and analysed in order to examine their antioxidant content. It was found that the carnosic and the rosmarinic acids, and to a much lesser extent the carnosol, constituted the main antioxidant components of the UK-plants, with the two acids being present at a ratio of 3:1, respectively.
Keywords: Esters of rosmarinic acid; Rosemary-based antioxidants; Antioxidant performance; Polyolefins;
Polystyrene photodegradation with a styrene block copolymer containing TiO2 nanoparticle by Hisayuki Nakatani; Genichiro Kawajiri; Shiho Miyagawa; Suguru Motokucho (135-142).
Polystyrene (PS) photodegradation with a novel poly(styrene-block-acrylic acid) (PS-b-PAA) containing TiO2 nanoparticle photocatalyst was studied. The TiO2 nanoparticle contained anatase phase and showed methylene blue photodecomposition activity. In particular, the higher molecular weight PS736-b-PAA129 photocatalyst had a high ability in the photodegradation and showed good dispersity in PS matrix. The PS composite film transparency was nearly equal to that of PS. The composite showed good PS photodegradation behavior under the UV irradiation. The chain scission preferentially occurred, leading to the decrease of PS molecular weight. In addition, an additional methyl linoleate (ML) component caused an improvement of the chain scission activity to the composite.
Keywords: Photodegradation; TiO2 nanoparticle; Styrene block copolymer;
Synthesis of a novel phosphorus-containing epoxy curing agent and the thermal, mechanical and flame-retardant properties of the cured products by Guiyou Wang; Zubao Nie (143-154).
A novel α, ω-dicarboxyl aromatic polyphosphonate (HP-1001-COOH) was synthesized and characterized. It was used as a reactive flame retardant for diglycidyl ether of bisphenol A (DGEBA)/methyl tetrahydrophthalic anhydride (MeTHPA) cured system. The thermal, mechanical and flame retardant properties of the cured epoxy resins were examined. The glass transition temperature (T g ) of the cured epoxy resins decrease with the increasing of the HP-1001-COOH content. The mechanical properties of cured films were slightly affected, although the crosslinking density decreases with the incorporation of HP-1001-COOH. The onset decomposition temperatures and the maximum-rate decomposition temperatures decrease, while the char yields increase with the increase of the phosphorus content. When the mass fraction of HP-1001-COOH is 30 wt%, the epoxy thermosets reaches a LOI value of 32.4% and successfully pass UL-94 V-0 rating. The heat release rate (HRR), peak heat release rate (P-HRR), total heat release (THR), average of effective heat of combustion (AvEHC) and total smoke production (TSP) of the flame retardant epoxy resins decrease significantly compared with neat epoxy resin. The macro-morphology and micro-morphology of the residues after cone calorimeter tests show that the flame retardant epoxy thermosets compact char layers are formed to prevent the transmission of heat and gases during combustion process, and the main structure in the char residues of the phosphorus-containing epoxy resins are polyaromatic carbons and phosphate esters.
Keywords: Epoxy resin; Reactive flame retardant; Aromatic polyphosphonates; Mechanical property; Thermal degradation; Cone calorimeter;
Synergistic effects in the pyrolysis of phosphorus-based flame-retardants: The role of Si- and N-based compounds by Sarah Deh; Frank Gähr; Michael R. Buchmeiser (155-164).
The modification of cotton fabrics with phosphorus-based flame-retardants (FRs) in the presence of synergistic elements such as nitrogen or silicon is reported. For these purposes, analyses of the combustion behavior and the thermal-oxidative stability of the modified fabrics were performed using pyrolyzis – gas chromatography-mass spectrometry (Py-GC/MS), thermogravimetric analysis coupled to Fourier-transform infrared spectroscopy and attenuated total reflection infrared spectroscopy (ATR-IR). It was found that limiting oxygen index (LOI) values were higher in case a P/N/Si instead of a P/N element combination was used. With the former, increased residual masses were obtained and the amount of phosphorus could be reduced by the presence of silicon. The results obtained path the way for further developments and optimizations of flame-retardants by determining the optimum element combinations and element/element ratios, ultimately leading to high flame retardant effects.
Keywords: Flame retardant; Pyrolysis mechanism; Py-GC/MS; TGA-FTIR/MS; Correlation;
Phosphonium sulfonates as flame retardants for polycarbonate by Shijie Hou; Yong Jian Zhang; Pingkai Jiang (165-172).
Phosphonium sulfonates (PhSs) as flame retardants have been synthesized from organic sulfonates and triphenylphosphine as starting materials. The PhSs revealed good thermal stability and efficient flame retardancy for polycarbonate (PC). The LOI values increased with the increase of PhS-1 contents to PC and reached 33.7 when the PhS-1 content is 10 phr, and the V-0 rating can be achieved when only 5 phr PhSs are added. The cone calorimeter analysis indicated that the HRR and THR were reduced with the addition of PhSs to the PC matrix. The PhS bearing alkene group revealed highest LOI values and lowest peak HRR (pHRR) values for PC. The morphology of the residual chars after LOI test and the element content of the chars after CONE test were also investigated by SEM and EDX.
Keywords: Flame retardants; Phosphonium sulfonates; Polycarbonate;
Synergistic flame-retardant behavior and mechanisms of aluminum poly-hexamethylenephosphinate and phosphaphenanthrene in epoxy resin by Jingyu Wang; Lijun Qian; Zhigang Huang; Youyou Fang; Yong Qiu (173-181).
The flame retardants aluminum poly-hexamethylenephosphinate (APHP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide(DOPO) were incorporated into diglycidyl ether of bisphenol A (EP) thermoset, and then the synergistic flame-retardant behavior and mechanism of APHP/DOPO were investigated. Comparing with the thermosets with 6%APHP and 6%DOPO alone, 2%APHP/4%DOPO/EP thermosets obtained the higher limited oxygen index, higher UL94 rating, decreased peak of heat release rate and less total heat release from cone calorimeter test. The results reveal a synergistic effect between APHP and DOPO. The synergistic effect of APHP/DOPO in gaseous phase obviously reduced effective heat of combustion, which implies the better flame inhibition effect through quenching free radical chain reaction of combustion. The synergistic charring effect in condensed phase led to the higher char yield, which locked more carbonaceous contents in residue and form more barrier to heat spreading. All the results were caused by the early decomposed DOPO that interacted with the later decomposed APHP to produce more char and decease release of the inflammable gas. Therefore, the burning intensity of APHP/DOPO thermosets obviously was weakened by the synergistic effect of APHP/DOPO.
Keywords: Flame retardant; Phosphinate; DOPO; Synergistic effect; Epoxy resin;
A method for the determination and correction of the effect of thermal degradation on the viscoelastic properties of degradable polymers by Gabriel Y.H. Choong; Davide S.A. De Focatiis (182-188).
Small amplitude oscillatory shear is carried out during isothermal degradation of poly(lactic acid) (PLA) in order to determine the evolution of the characteristic relaxation time with degradation time and temperature. After reducing the relaxation time data to a single mastercurve, a 4-parameter function is fitted to the data to allow prediction of the change in relaxation time following an arbitrary thermal history. The method enables separation of the effects of temperature and of degradation on the relaxation time, both of which lead to a horizontal shift of dynamic data along the frequency axis, and hence enable a correction for thermal degradation during rheometry to be carried out. To validate the method, two isothermal frequency sweeps were measured with different temperature histories, producing different mastercurves due to dissimilar in-test thermal degradation. After correcting for thermal degradation using the function and the thermal histories, the two frequency sweeps reduce to the same viscoelastic mastercurve in the undegraded pre-test state.
Keywords: Biodegradable polymers; Thermal degradation; Melt rheology; Linear viscoelasticity;
On NMR prediction of the antioxidant effectiveness of p-substituted diphenyl amines by Ingrid Puškárová; Michal Šoral; Martin Breza (189-193).
NMR shifts of a series of ten p-substituted diphenyl amine antioxidants in DMSO have been measured as well as evaluated by B3LYP calculations. At 25 °C no correlation between Molar Antioxidant Effectiveness (AEM) and NMR chemical shifts of relevant atoms is evident. AEM at 130 °C increases with NMR chemical shifts of nitrogen atoms between aromatic rings and hydrogen atoms bonded to them with very good statistical parameters (except nitro- and nitroso-compounds). This treatment might aid to a very simple estimation of high-temperature AEM values based on NMR shifts (experimental or calculated by quantum-chemical methods) of relevant atoms. Our results confirm that the essential mechanism of the antioxidant action is temperature-dependent.
Keywords: DFT geometry optimization; NMR shifts; Antioxidant effectiveness prediction;
Flame retarding performance of elastomeric nanocomposites: A review by Prashant S. Khobragade; D.P. Hansora; Jitendra B. Naik; Aniruddha Chatterjee (194-244).
This article presents a comprehensive review about previous research done for the development of elastomeric nanocomposites (NCs) based flame retardant (FR) materials. Conservatively, a single fire retardant element can achieve fire retardancy, but we report about combinations of elastomers and various fire retardant materials at nanoscale, including layered materials and inorganic materials for the development of polymeric and elastomeric NC based FR materials. We have critically reviewed and summarized the surface morphological structure, organic treatment for surface modification, dispersion phenomenon, fire retardant action and the flame-retarding properties of various elastomeric NCs. We also highlight the fundamentals and combustion mechanism of fire retardancy tests, which have been used to describe fire behavior, nature and modes of FR materials and their synergistic effects. We have focused particularly on elastomeric NCs filled with specific, finely dispersed different nanofillers, which will undoubtedly pave the way for development of FR materials showing physico-mechanical and enhanced FR performance. This review article will objectively explore and give new direction for the development of the “FR materials” which would be more accessible to the emerging field of materials science.
Keywords: Fire retardancy; Flame retardant; Nanomaterials; Elastomer; Nanocomposites;
Modelled decomposition kinetics of flame retarded poly(vinyl acetate) by B. Rimez; G. Van Assche; S. Bourbigot; H. Rahier (245-256).
Previously determined degradation mechanisms of a model polymer compound, poly(vinyl acetate) (PVAc), blended with two different flame retardants, ammonium poly(phosphate) (APP) and melamine isocyanurate (MIC), were used for reaction rate parameter optimization using a kinetic modelling and simulation software. Rate parameters for all different decomposition reactions were established for inert and oxidative conditions, giving insight into all interactions between flame retardants and polymer. Analyzing kinetic data, it was found that APP catalyzes the deacetylation reaction of PVAc, independent from the mixing ratio, and has a higher catalyzing effect than oxygen. Down to ten parts APP per one hundred parts of PVAc, APP is also a very efficient crosslinker with PVAc upon decomposition. MIC on the other hand acts in two ways: as heat-sink flame retardant during deacetylation and charring of the polymer, whereas during this charring step, another part of MIC crosslinks with PVAc. Simulations using kinetic parameter sets of PVAc/MIC and PVAc/APP blends showed that MIC and APP interact independently with PVAc when both flame retardants are mixed together into PVAc. A very efficient flame retarded composite is as such obtained at low loading levels.
Keywords: Degradation kinetics; Modelling; Flame retardant; Poly(vinyl)acetate; Ammonium poly(phosphate); Melamine isocyanurate;
Synergistic effect of an aromatic boronic acid derivative and magnesium hydroxide on the flame retardancy of epoxy resin by Tie Zhang; Weishi Liu; Meixiao Wang; Ping Liu; Yonghong Pan; Dongfa Liu (257-263).
To develop new organic/inorganic flame retardants, the aromatic boronic acid derivative 2,4,6-tris(4-boronic-2-thiophene)-1,3,5-triazine (3TT-3BA) and magnesium hydroxide (MH) were selected. The two compounds were added to epoxy resin (EP) to investigate the flame retardant properties and mechanism. The mechanical, thermal, and flame retardant properties of the EP and flame retardant EP were investigated. The morphology of char was characterized by scanning electron microscopy. The results show that mixing EP with both 3TT-3BA and MH results in better thermal stability and flame retardant properties than mixing with only one of the compounds, indicating the synergistic effect of the two components. The elements in the char were investigated by elemental analysis to further investigate the flame retardant mechanism. The result of impact strengths shows that 3TT-3BA can inhibit combustion with MH effectively without decreasing the mechanical strength.
Keywords: Aromatic boronic acid; Magnesium hydroxide; Epoxy resin; Synergistic effect;
The microstructure and stability of collagen hydrogel cross-linked by glutaraldehyde by Zhenhua Tian; Wentao Liu; Guoying Li (264-270).
Collagen hydrogels, which are comprised of fibrils and possess three-dimensional network structure, were prepared via self-assembly of collagen molecules and sequentially incubated in glutaraldehyde (GTA) solutions with different [CHO]/[NH2] ratios (0–9). The cross-linking degree of outer and inner parts of hydrogels was similar, demonstrating the homogeneous reaction. Based on the results of atomic force microscopy, differential scanning calorimetry and dynamic rheological measurements, it was conjectured that the stability of hydrogels were closely associated with the structural changes of collagen fibrils. When the [CHO]/[NH2] ratios ≤3, cross-linking preferentially occurred between adjacent fibrils; therefore, the fibrils presented in pairs and then densely agglomerated. As a result, the thermal denaturation temperature (from 47.1 to 73.6 °C) and elastic modulus (from 108.32 to 1618.55 Pa) increased drastically, accompanied by a distinct decrease in enzymatic degradation degree (from 93.69 to 26.91%). The effective binding ratio (EB) of aldehyde groups reduced from 72.66 to 43.92%. Moreover, hydrogels turned into yellow and yellowness (Δb*) increased from 0 to 1.68. When the [CHO]/[NH2] ratio reached 3, the arrangement of fibrils became very compact; therefore, although the GTA dosage was multiplicative ([CHO]/[NH2] = 9), there was only a relatively small improvement in thermal stability and anti-enzymolysis. Furthermore, the EB value was only 16.40%, indicating that intensive self-polymerization of GTA molecules caused a large consumption of aldehyde groups, accompanied by a remarkable yellow-stain (Δb* = 2.73). These data on the stability of cross-linked hydrogels could be helpful for the design and fabrication of materials based on collagen hydrogels.
Keywords: Collagen hydrogel; Glutaraldehyde; Cross-linking; Microstructure; Stability;
In-line monitoring of the photooxidation behaviour of a PP/clay nanocomposite through creep measurements by F.P. La Mantia; M. Biondo; M. Ceraulo; M.C. Mistretta (271-276).
The photooxidation behaviour of a polypropylene/organomodified clay nanocomposite sample has been monitored by means of a new apparatus through the record of the creep curves measured while the sample is subjected to the contemporary action of temperature, tensile strength and UV radiation. The creep curves of the irradiated samples are higher than those of the non-irradiated samples and the curves diverge when the molecular weight begins to decrease because of the degradation. At the same the formation of carbonyl groups is observed. The creep curves of the non-irradiated and irradiated samples give, then, an immediate evaluation of the begin and of the development of the photooxidation. This behaviour is more pronounced for the nanocomposite because of the more photooxidation kinetics of this material.
Keywords: Photooxidation; Creep; PP/clay;
Plasma activated perfluoroethylenepropylene for cytocompatibility enhancement by P. Slepička; L. Peterková; S. Rimpelová; A. Pinkner; N. Slepičková Kasálková; Z. Kolská; T. Ruml; V. Švorčík (277-287).
The paper is focused on perfluoroethylenepropylene (FEP) plasma activation and cytocompatibility enhancement. Our main focus was on enhancement of one side of otherwise resistive and stable polymer by means of relatively easy a cheap method, plasma activation. The surface properties of FEP foil were altered with different plasma power and the influence of argon plasma treatment was determined. It was proved that wettability and morphology of FEP film can be specifically controlled and changed by means of combination of power and exposure time, the effect was accomplished by variation in oxygen concentration and specific morphology of treated surface. We have performed cytocompatibility tests involving monitoring of cell adhesion, proliferation and metabolic activity in vitro on a model cell line of human keratinocytes (HaCaT). Moreover, the expression profiles of two adhesion proteins were determined in dependence on the FEP treatment. A special attention was also paid to morphology of filopodia of HaCaT cells growing on FEP. The combination of altered surface morphology, wettability and chemistry led to creation of excellent biocompatible surface with a significantly positive effect on HaCaT cells adhesion, spreading and proliferation.
Keywords: Perfluoroethylenepropylene; Plasma treatment; Nanostructuring; Surface chemistry; Cytocompatibility; Keratinocytes; Adhesion proteins;
Poly((R,S)-3,3-dimethylmalic acid) derivatives as a promising cardiovascular metallic stent coating: Biodegradation and biocompatibility of the hydrolysis products in human endothelial cells by R. Belibel; N. Marinval; H. Hlawaty; C. Barbaud (288-299).
In-stent restenosis is currently treated with drug eluting stents based on biodegradable polymers which can deliver a therapeutic agent and be degraded in a few months preventing the risk of thrombosis. Poly([R,S]-3,3-dimethylmalic acid) (PDMMLA) is a new and original biodegradable and biocompatible polymer which contains a carboxylic acid functional group in its side chain. This gives it the particularity to be chemically modified and custom-synthesized to meet an adequate degradation time. It was prepared in order to develop new coating exhibiting different groups in its side chain and give natural and non-toxic primary products after a complete degradation. Herein we present the study of hydrolytic degradation of PDMMLAs under physiological conditions for a 6-month period. The most important factors that influence the kinetic degradation of polymers (molecular weight, nature and stability of functional groups, natural biological enzymes, pH and temperature) were studied in order to understand the behavior of PDMMLAs hydrolysis. It has been shown that the different PDMMLA polymers were degraded according to a bulk or erosion-surface profiles. Therefore, a hydrophilic loaded side chain, high temperature, high pH and the presence of specific enzyme accelerated the degradation rate of PDMMLAs with an erosion-surface profile. Since these new biomaterials as promising coating-stent will be in direct contact with the arterial wall, their biocompatibility was evaluated in this study in human vascular endothelial cells which are essential for the repair of the arterial wall to inhibit multiple processes leading to in-stent restenosis. The products of long-term degradation of PDMMLA polymers were non-cytotoxic.
Keywords: Biodegradable (poly([R,S]-3,3-dimethylmalic acid); Biocompatible; Hydrolytic degradation; Degradation profiles; Cytotoxicity; Human endothelial cells;
Coupled hydro-mechanical aging of short flax fiber reinforced composites by Arnaud Regazzi; Stéphane Corn; Patrick Ienny; Anne Bergeret (300-306).
One of the challenges in the widespread use of biocomposites for engineering applications is the influence of environmental conditions on their mechanical properties, particularly for a combination of aging factors such as temperature, moisture, and mechanical stresses. Thus, the purpose of this paper is to study the influence of coupled aging factors by focusing on a 100% bio-based and biodegradable composites made of flax/poly(lactic acid) with several fiber contents. The development of a specific testing setup enabled continuous in-situ measurements and allowed comparing the effects of combined aging factors to those of uncombined aging factors. It was confirmed that the aging temperature in wet conditions led to a loss of elastic properties, especially for higher fiber fractions. While creep tests in dry conditions resulted in little decrease of elastic properties, it was observed that mechanical loading of the materials combined with water immersion resulted in a strong synergistic effect on the loss of stiffness. Finally, the presence of fibers reduced environmental stress cracking mechanisms and increased the time to failure.
Keywords: Durability; Flax; Short-fibre composites; Hygrothermal effect; Creep test;
Melamine poly(zinc phosphate) as flame retardant in epoxy resin: Decomposition pathways, molecular mechanisms and morphology of fire residues by Patrick Müller; Michael Morys; Aleksandra Sut; Christian Jäger; Bernhard Illerhaus; Bernhard Schartel (307-319).
Synergistic multicomponent systems containing melamine poly(metal phosphate)s have been recently proposed as flame retardants. This work focuses on the decomposition pathways, molecular mechanisms and morphology of the fire residues of epoxy resin (EP) flame retarded with melamine poly(zinc phosphate) (MPZnP) to explain the modes of action and synergistic effects with selected synergists (melamine polyphosphate (MPP) and AlO(OH), respectively). The total load of flame retardants was always 20 wt.%. The decomposition pathways were investigated in detail via thermogravimetric analysis coupled with Fourier transform infrared spectroscopy. The fire residues were investigated via elemental analysis und solid-state nuclear magnetic resonance spectroscopy. The morphology of intumescent fire residues was investigated via micro-computed tomography and scanning electron microscopy. EP + (MPZnP + MPP) formed a highly voluminous residue that showed structural features of both EP + MPZnP and EP + MPP, resulting in a highly effective protection layer. EP + (MPZnP + AlO(OH)) preserved the entire quantity of phosphorus content during combustion due to the formation of Zn2P2O7 and AlPO4.
Keywords: Melamine poly(metal phosphate); Flame retardancy; Epoxy resin; Solid-state NMR; Micro-computed tomography; Fire residue;
Simultaneous DSC/TG analysis on the thermal behavior of PAN polymers prepared by aqueous free-radical polymerization by Qin Ouyang; Xiaohong Wang; Xulan Wang; Jing Huang; Xianwen Huang; Yousi Chen (320-327).
A series of polyacrylonitrile (PAN) polymers with different content of itaconic acid (IA) as comonomer were prepared by an efficient aqueous free-radical polymerization technique. The thermal behavior of the PAN polymers was investigated by simultaneous DSC/TG analysis. Effects of IA content, heating rate and atmosphere on the heat release and weight loss behaviors of the PAN polymers were studied for insight of the nature of the thermo-chemical reactions. A specific triple exothermic peak was observed in the DSC curves of P(AN-IA) copolymers in air atmosphere. Three individual exothermic peaks were obtained by peak fitting and assigned to the respective thermo-chemical reactions, namely, ionic cyclization reaction, free-radical cyclization reaction and oxidation reaction. The ionic cyclization reaction was significantly influenced by the IA content. The free-radical cyclization reaction was sensitive to heating rate and atmosphere. The cyclization reaction preceded the oxidation reaction and acted as a prerequisite for the oxidation reaction. The improvement of the thermal stability of PAN was mainly attributed to the oxidation reaction through dehydrogenation and formation of oxygen-bearing groups. Mechanisms of the thermo-chemical reactions were also proposed and discussed.
Keywords: Polyacrylonitrile; Thermal behavior; Thermal stabilization; Aqueous free-radical polymerization; Carbon fiber;
Structure and thermal pyrolysis mechanism of poly(resorcinol borate) with high char yield by Shujuan Wang; Cheng Bian; Beibei Jia; Yanan Wang; Xinli Jing (328-337).
Boron-containing organic polymers have excellent thermal stability and flame retardancy. Hyperbranched polymers, in which boron atoms are introduced in the form of borates, exhibit superior performance and have more applicability. This work focuses on the boron-containing polymer poly (resorcinol borate) (PRB). The chemical structure of PRB and its structural evolution at high temperatures are investigated in order to clarify the reason for its high char yield. The results indicate that the molecular skeleton of PRB mainly consists of aromatic structures, borates, B―O―B structures, and a small number of boron hydroxyl groups and phenolic hydroxyl groups. During pyrolysis, boron oxide is formed by the cleavage of borate O―C bonds at about 400 °C. This process effectively avoids the formation and release of volatile carbon dioxide, reducing carbon loss. A large fraction of the carbon from aromatic rings is converted to amorphous carbon via pyrolysis, which possesses higher thermal stability. These results can guide the design and synthesis of novel boron-containing polymers and can provide a strategy for modifying the thermal properties of phenolic resins in order to broaden their applicability in the field of ablative-resistant composites and coatings.Display Omitted
Keywords: Poly(resorcinol borate); Thermal pyrolysis mechanism; High char yield; Borates; Boron oxide;
Thermal stability of a eutectic mixture of bis(2,2-dinitropropyl) acetal and formal: Part B. Degradation mechanisms under water and high humidity environments by Dali Yang; Robin Pacheco; Stephanie Edwards; Joseph Torres; Kevin Henderson; Milan Sykora; Peter Stark; Sheldon Larson (338-347).
As a continuation of our effort to understand degradation mechanisms of a eutectic mixture of bis(2,2-dinitropropyl) acetal (BDNPA) and bis(2,2-dinitropropyl) formal (BDNPF) (referred to as NP) under various environmental conditions, we investigated the thermal stability of NP under water and 74% relative humidity (RH) environments at temperatures below 70 °C. Based on a comprehensive characterization of samples aged over a period of two years, we conclude that in the presence of water the reaction pathways of NP degradation are different from those observed in air or under nitrogen atmosphere. We found that the physical state of water molecules plays an important role as it determines the ability of oxygen to participate in the NP degradation process. Based on the results obtained in Parts A and B of these studies, we conclude that the rate of NP degradation increases in the following order: nitrogen < water < air < water vapor + air.
Keywords: Nitroplasticizer; BDNPA; BDNPF; Condensed phase; Estane; Stability; Degradation;
Predictive ageing of elastomers: Oxidation driven modulus changes for polychloroprene by Pierre Yves Le Gac; Mathew Celina; Gérard Roux; Jacques Verdu; Peter Davies; Bruno Fayolle (348-355).
The oxidative ageing in the range of 60 °C–140 °C of sulfur vulcanized polychloroprene has been studied by FTIR spectroscopy (double bond consumption), modulus changes and oxygen absorption measurements. Experiments were carried out on thin films and thick samples to investigate both homogeneous and inhomogeneous (diffusion controlled) oxidation with the goal of establishing the underlying correlation between oxidative degradation chemistry and mechanical property changes. A correlation between oxidatively driven degradation chemistry and modulus is possible using the established approaches of rubber elasticity where an effective crosslinking yield due to double bond reactions is of the order of 30% for this material (i.e. the loss of 3 double bonds results in one effective crosslink associated with material hardening). It is then possible to predict modulus changes induced by oxidation for vulcanized and unstabilized polychloroprene rubber. A kinetic model is introduced with two propagation reactions (hydrogen abstraction and radical addition to double bonds) and two stabilization processes involving sulfur containing moieties from the vulcanization process. The kinetic scheme was solved and the relevant rate constants determined. This model can adequately predict modulus changes in films and thick samples as a function of time and spatially resolved.
Keywords: Polychloroprene; Ageing; Sulfur vulcanization; Oxidation; Kinetic modeling; Modulus changes;