Polymer Degradation and Stability (v.98, #9)
Editorial Board (IFC).
Effect of partial crosslinking on morphology and properties of the poly(β-hydroxybutyrate)/poly(d,l-lactic acid) blends by Weifu Dong; Piming Ma; Shifeng Wang; Mingqing Chen; Xiaoxia Cai; Yong Zhang (1549-1555).
Poly(β-hydroxybutyrate) (PHB) is a bio-based and biodegradable aliphatic polyester, however its application is limited by some disadvantages such as high price, brittleness, poor processability and low melt-strength due to serious thermal degradation. Partial crosslinking initiated by dicumyl peroxide (DCP) was applied in this work to improve the performance of poly(β-hydroxybutyrate)/poly(d,l-lactic acid) (PHB/PDLLA) blends. The partial crosslinking of the blends and its effect on the properties, morphology, rheology and thermal behavior of the blends were investigated. The tensile strength and impact toughness of the PHB were increased by incorporation of the PDLLA, which were improved further after the partial crosslinking because of an increased compatibility between the PHB and the PDLLA phases. The rheological study revealed that the storage modulus (G′) and complex viscosity (η*) of the blends were increased after addition of the DCP. On the other hand, the crystallization of PHB in the blends was restricted to a certain extent by the formation of partially crosslinked network while its crystal form was not modified.
Keywords: PHB; PLA; Crosslinking; Properties; Crystallization;
Enhancement of cellulose acetate degradation under accelerated weathering by plasticization with eco-friendly plasticizers by Robert Quintana; Olivier Persenaire; Yahia Lemmouchi; John Sampson; Stuart Martin; Leïla Bonnaud; Philippe Dubois (1556-1562).
Cellulose acetate (CA) with a degree of substitution (DS) of 2.5 has been plasticized using eco-friendly plasticizers such as triacetin, tripropionin, triethyl citrate, tributyl citrate, tributyl 2-acetyl citrate and poly(ethylene glycol) of low molecular weight. Thermo-mechanical properties and hydrophilicity of the modified CA have been measured and correlated with the content and nature of the plasticizer used and compared with unplasticized CA. The increase in toughening and the change in the hydrophilicity by the plasticization were evaluated in terms of aging and weathering stability under accelerated conditions. Samples were exposed to UV-degradation with water spray periods. The treated samples were removed periodically and characterized by several analytical techniques. The results are discussed with particular emphasis toward the effects of plasticization on enhancement of the degradation rate of CA. The plasticization of CA triggered an increase of the weight loss between 50 and 90%, where low molecular weight plasticizers were shown to be more effective. A right balance between hydrophilicity and plasticization efficiency (reduction of T g ) is needed to increase the degradation rate of CA.
Keywords: Cellulose acetate; Degradation; Weathering; Plasticization; Blend;
Study of the degradation of a new PLA braided biomaterial in buffer phosphate saline, basic and acid media, intended for the regeneration of tendons and ligaments by María C. Araque-Monrós; Ana Vidaurre; Luis Gil-Santos; Sagrario Gironés Bernabé; Manuel Monleón-Pradas; Jorge Más-Estellés (1563-1570).
The purpose of this study was to evaluate the effects of hydrolytic degradation on the properties of a PLA hollow braid designed as a new concept of biodegradable prosthesis for the regeneration of tendons and ligaments. The main function of the braided material is to bear mechanical loads while it is being replaced by the newly-generated tissue. The kinetics of braided material degradation is thus an important factor in determining the success of the product. In order to study this mechanism, PLA braid was subjected to a 12-month degradation process at 37 °C in PBS at pH 7.4 (to simulate the human physiological medium) and to accelerated degradation for one month in pH 12 and pH 3 solutions. Degradation of the braid subjected to hydrolysis was evaluated by weight loss, molecular weight distribution, mechanical properties, and calorimetric and morphologic analyses. The weight loss in a basic medium reached 21%, versus no significant change in the other media. Average molecular weight was reduced by approximately 50% in the three media, with loss of mechanical properties in all cases. The morphological changes were more evident in the PLA degraded in the basic medium. The crystallinity of the material increased at the first stages of degradation, regardless of the medium used.
Keywords: Prosthesis; Tendon; Ligament; Hydrolytic degradation;
Pyrolysis kinetics of ethylene–propylene (EPM) and ethylene–propylene–diene (EPDM) by Antonio Perejón; Pedro E. Sánchez-Jiménez; Eva Gil-González; Luis A. Pérez-Maqueda; José M. Criado (1571-1577).
The thermal degradation kinetics of several ethylene–propylene copolymers (EPM) and ethylene–propylene–diene terpolymers (EPDM), with different chemical compositions, have been studied by means of the combined kinetic analysis. Until now, attempts to establish the kinetic model for the process have been unsuccessful and previous reports suggest that a model other than a conventional nth order might be responsible. Here, a random scission kinetic model, based on the breakage and evaporation of cleavaged fragments, is found to describe the degradation of all compositions studied. The suitability of the kinetic parameters resulting from the analysis has been asserted by successfully reconstructing the experimental curves. Additionally, it has been shown that the activation energy for the pyrolysis of the EPM copolymers decreases by increasing the propylene content. An explanation for this behavior is given. A low dependence of the EPDM chemical composition on the activation energy for the pyrolysis has been reported, although the thermal stability is influenced by the composition of the diene used.
Keywords: EPDM; Thermal degradation; Kinetic model; Random scission;
Biodegradable in situ gel-forming controlled vancomycin delivery system based on a thermosensitive mPEG-PLCPPA hydrogel by Ding-Wei Hong; Po-Liang Lai; Kuan-Lin Ku; Zhi-Teng Lai; I.-Ming Chu (1578-1585).
In this study, a biodegradable in situ gel-forming controlled drug delivery system based on a thermosensitive methoxy polyethylene glycol-co-poly (lactic acid-co-aromatic anhydride) (mPEG-PLCPPA) hydrogel was studied. The hydrogels were formed by micelle aggregation with rising temperature. The hydrogels underwent a temperature-dependent sol–gel–sol transition, which was a flowing sol at ambient temperature and a non-flowing gel at the physiological body temperature. The residual weight and pH value changes after degradation and the viscosity properties of the hydrogel were investigated. The in vitro release behavior of vancomycin from the mPEG-PLCPPA hydrogels at different concentrations was also investigated. The results showed that the mPEG-PLCPPA amphiphilic copolymer could self-assemble to form micelles at low concentrations, and that the particle sizes gradually increased with increasing temperature. The hydrogel maintained a stable degradation rate and provided a moderate pH microenvironment after degradation for 30 days. Vancomycin sustained a stable release profile from the hydrogel over a 10-day period. Furthermore, good biocompatibility was proven by MTT assay and live and dead test. Therefore, the mPEG-PLCPPA hydrogel shows promise as an injectable local antibiotic delivery system.
Keywords: Bioengineering; Biomaterials; Drug delivery; Polymers;
Effect of glycerol and its analogs on polyhydroxyalkanoate biosynthesis by recombinant Ralstonia eutropha: A quantitative structure–activity relationship study of chain transfer agents by Takeharu Tsuge; Takashi Ko; Masako Tago; Hideki Abe (1586-1590).
Triglycerides such as plant and vegetable oils are desirable feedstock for the fermentative production of polyhydroxyalkanoate (PHA) because the weight yield of PHA from triglycerides is higher than that obtained from sugars. However, glycerol, a multi-hydroxy component of triglyceride, is known to function as a chain transfer (CT) agent in PHA polymerization, resulting in the formation of low-molecular-weight PHA. In this study, we evaluated how glycerol alters the molecular weight of PHA using recombinant Ralstonia eutropha as a practical host for PHA production. We demonstrated that glycerol has the ability to reduce molecular weight of PHA, even as a component of triglyceride. Furthermore, various alcohols that are structurally related to glycerol were examined for their reducing abilities to perform a quantitative structure–activity relationship (QSAR) study. It was found that alcohols with higher hydrophobicity (log P) exhibited higher reducing ability for PHA molecular weight. Glycerol, a less hydrophobic alcohol, was able to reduce PHA molecular weight; however, the efficacy was relatively weak among the examined alcohols.
Keywords: Polyhydroxyalkanoate; Molecular weight; Chain transfer agent; Quantitative structure–activity relationship; Glycerol;
Mechanical, aging, optical and rheological properties of toughening polylactide by melt blending with poly(ethylene glycol) based copolymers by Lidong Feng; Xinchao Bian; Zhiming Chen; Gao Li; Xuesi Chen (1591-1600).
Two novel biodegradable copolymers, including poly(ethylene glycol)-succinate copolymer (PES) and poly(ethylene glycol)-succinate-l-lactide copolymer (PESL), have been successfully synthesized via melt polycondensation using SnCl2 as a catalyst. The copolymers were used to toughen PLA by melt blending. The DSC and SEM results indicated that the two copolymers were compatible well with PLA, and the compatibility of PESL was superior to that of PES. The results of tensile testing showed that the extensibility of PLA was largely improved by blending with PES or PESL. At same blending ratios, the elongation at break of PLA/PESL blends was far higher than that of PLA/PES ones. The elongation maintained stable through aging for 3 months. The moisture absorption of the blends enhanced due to the strong moisture absorption of PEG segments in PES or PESL molecules, which did not directly lead to enhance the hydrolytic degradation rate of the PLA. The PLA blends containing 20–30 wt% PES or PESL were high transparent materials with high light scattering. The toughening PLA materials could potentially be used as a soft biodegradable packaging material or a special optical material.
Keywords: Polylactide; Poly(ethylene glycol); Copolymer; Toughness; Transparent material;
Effects of halloysite nanotube orientation on crystallization and thermal stability of polypropylene nanocomposites by Bin Wang; Han-Xiong Huang (1601-1608).
The polypropylene/halloysite nanotubes (PP/HNTs) nanocomposites were prepared via water-assisted injection molding (WAIM) and compression molding (CM). HNTs were highly oriented in WAIM parts due to the strong shear effect; whereas HNTs were randomly oriented in the CM one. The orientation of HNTs had little influence on their nucleating efficiency for the PP. However, the HNTs selectively induced α-form crystal at high cooling rates; whereas they showed β-nucleating activity at low cooling rates. Thermal analyses revealed that the HNTs delayed thermal degradation onset in the initial degradation stage, whereas they sped up the thermal degradation in the main volatilization stage at the contents of 5 and 8 wt%. The simultaneous thermogravimetric analyses and differential scanning calorimetry measurements revealed that, at a low content, the direct stabilizing effect of HNTs on PP contributed largely to the increased thermal stability of the WAIM PP/HNTs nanocomposites rather than their barrier and entrapment effect on the volatile products.
Keywords: Halloysite nanotube; Polypropylene; Nanocomposites; Thermal stability;
Thermal stability and flame retardancy of polyester fabrics sol–gel treated in the presence of boehmite nanoparticles by Emanuela Guido; Jenny Alongi; Claudio Colleoni; Alessandro Di Blasio; Federico Carosio; Marc Verelst; Giulio Malucelli; Giuseppe Rosace (1609-1616).
Polyester fabrics have been treated with hybrid organic-inorganic sols containing aluminium hydroxide, namely a synthetic boehmite. The treated fabrics have been thoroughly investigated by infrared spectroscopy, scanning electron microscopy coupled to elemental analysis and thermogravimetry. Furthermore, the flammability of the coated fabrics has been assessed and compared with that achieved by applying the two components separately. More specifically, flammability tests have shown that the sol–gel treatment in the presence of boehmite nanoparticles is able to suppress the dripping phenomenon, which represents the main issue to fulfil for polyester fabrics.
Keywords: PET; Boehmite; Sol–gel processes; Flammability; Thermal stability; Anti-dripping;
Calcium-based hydrated minerals: Promising halogen-free flame retardant and fire resistant additives for polyethylene and ethylene vinyl acetate copolymers by Fouad Laoutid; Marion Lorgouilloux; Didier Lesueur; Leila Bonnaud; Philippe Dubois (1617-1625).
In this study, we evaluated the potential flame retardant effect of calcium-based hydrated minerals, such as hydrated lime, partially and completely hydrated dolomitic limes in polyethylene (MDPE) and ethylene vinyl acetate copolymers (EVA) and compared to that obtained with magnesium di-hydroxide (MDH). The most significant flame retardant effects, observed using the mass loss calorimeter test, indicated that Ca-based MDPE composites showed similar peak Heat Release Rate (pHRR) level to that obtained with MDH composite while the pHRR was lower for Ca-based fillers in EVA compositions. X-ray Diffraction (XRD) data, combined with thermal analysis results, indicated that the calcium di-hydroxide plays a role in the formation of an intumescent cohesive residue during the combustion. Indeed, Ca(OH)2 reacts with CO2 formed during the thermal degradation of the polymer to generate CaCO3 (calcium carbonate) that contributes to the enhancement of the mechanical resistance of the residue.
Keywords: Fire properties; Calcium-based hydrated minerals; EVA; Char structuring;
Flammability and combustion properties of ammonium polyphosphate-/poly(acrylic acid)- based layer by layer architectures deposited on cotton, polyester and their blends by Federico Carosio; Jenny Alongi; Giulio Malucelli (1626-1637).
Layer by layer architectures consisting of four layer repetitive unit (QL) based on poly(diallydimethylammonium chloride)/poly(acrylic acid)/poly(diallydimethylammonium chloride)/ammonium polyphosphate have been deposited on cotton, polyester and their blends in order to promote the formation of an aromatic and stable carbonaceous structure (char) during combustion. The LbL-treated fabrics have been subjected to flammability (reaction to flame application) and combustion (reaction to different external heat fluxes) tests. The coatings were able to remarkably enhance the char formation of each substrate just after 1QL deposition; furthermore, 5 and 10QL assemblies have favoured the formation of intumescent-like structures with further improvement of the final residue. As a consequence, the treated fabrics have shown a strong reduction of the flammability (afterglow and incandescent melt dripping suppression) and combustion (reduced heat released). Infrared spectroscopy has pointed out the aromatic nature of the residues left after the combustion.
Keywords: Flame retardancy; Char; Layer by layer assembly; Ammonium polyphosphate; Poly(acrylic acid);
Investigation of the synergy in intumescent polyurethane by 3D computed tomography by M. Muller; S. Bourbigot; S. Duquesne; R. Klein; G. Giannini; C. Lindsay; J. Vlassenbroeck (1638-1647).
The morphology of carbonized materials resulting from an intumescence phenomenon was studied. The investigated material is a polyurethane matrix filled either by 30 wt.-% of ammonium polyphosphate or by a combination of 28 wt.-% of ammonium polyphosphate and 2 wt.-% of nano-magnesium oxide. These fillers were incorporated in the polyurethane directly during the synthesis step. The carbonized materials or char, are obtained in a specific fire scenario. Characterization of their morphology is carried out using X-ray computed tomography. The heat conductivity of the systems is additionally measured as a function of temperature in order to correlate structure and properties of the intumescent residues. The formation of different char structures with incorporation of magnesium oxide (in particular formation of bubbles of different size) is first evidenced. These observations are consistent with the heat conductivity data. Tomography images demonstrate that the intumescence process is a dynamic process since non degraded polymer is left at the beginning of the fire test, which is not the case for longer time. The dispersion of fillers has finally been investigated in the chars and it is evidenced different steps of intumescence's development in the material.
Keywords: Intumescence; Flame retardant; Polyurethane; Nanofiller; Synergy; Tomography;
Morphological and compositional evolution of polymeric colloidal monolayer during UV irradiation by Mun Ho Kim; Jong-Jin Lee; Hyo Sang Eom; Ji-Eun You; Kil-Yeong Choi; Doo-Jin Byun (1648-1654).
In this study, we investigated the morphological and compositional evolution polymeric colloidal monolayer during UV irradiation. A PS colloidal monolayer with interparticle bridges was prepared and exposed to the UV light. As a consequence of photochemical reactions containing chain-scission, UV irradiation induced morphological changes in the monolayer surface including changes in the size, shape, and packing structure of PS particles. By manipulating the UV irradiation time, fine tuning of size and shape of the interstice in the monolayer was achieved. In these procedures, the interparticle bridges play an important role. The UV irradiation induced the formation of polar groups in the PS particle surface and thus the particle surface became highly hydrophilic.
Keywords: Colloidal crystal; Colloidal lithography; Photooxidation; PS latex; Surface characterization;
Monitoring the degradation of stabilization systems in polypropylene during accelerated aging tests by liquid chromatography combined with atmospheric pressure chemical ionization mass spectrometry by Susanne Beißmann; Martin Stiftinger; Klemens Grabmayer; Gernot Wallner; David Nitsche; Wolfgang Buchberger (1655-1661).
Degradation pathways of three commonly used antioxidants were successfully studied by using accelerated aging tests for polymers. Additionally, thermal stability and resistance to discoloration of seven stabilizers were investigated by aging pure stabilizers dissolved in the polymer-mimicking solvent squalane. Methods based on high-performance liquid chromatography hyphenated with highly sensitive tandem mass spectrometric detection (HPLC-MS) were developed for structural elucidation of degradation products. Subsequent quantification was done using UV-detection. While Irganox 1330, Irganox 3114 and Cyanox 1790 showed a similar degradation mechanism with highly colored decomposition products, no corresponding oxidized species could be found for other stabilizers and less discoloration was observed. For Irganox 1010, hydrolysis was the preferred degradation mechanism, leading to products with an increased solubility in water. Therefore this stabilizer is less suitable for materials intended for water applications. In the aged materials previously unknown degradation mechanisms were observed for Irganox 1010 and Irgafos 168 which also contribute to the inhibition of autoxidation of the polymer.
Keywords: Phenolic antioxidants; Degradation pathway; Discoloration; Oxidation; Hydrolysis;
Photochromic copolymers containing 3-indolylfulgides/indolylfulgimides: Synthesis and photochemical properties in toluene and as films by Nadezhda I. Islamova; Xi Chen; Chang-Jun Fan; Richard S. Andino; Watson J. Lees (1662-1670).
Photochromic indolylfulgimides covalently attached to polymers have beneficial properties for optical switching. A 3-indolylfulgide and two 3-indolylfulgimides with one or two polymerizable styrene groups attached on the nitrogen atom(s) were synthesized. Copolymerization with methyl methacrylate (MMA) provided linear copolymers (one styrene group) or a cross-linked copolymer (two styrene groups). The properties of the monomers and copolymers in toluene or as thin films were characterized. The new copolymers were photochromic (reversible Z-to-C isomerization), absorbed visible light, and revealed good thermal and photochemical stability. At room temperature, all copolymer films showed no loss of absorbance after 5 weeks. At 80 °C in either toluene or as films, the Z-forms copolymers were less stable than the C-form copolymers, which showed little or no degradation after 400 h. The degradation rate due to repeated ring-closing – ring opening cycles was less than 3% per 100 cycles. The cross-linked copolymer showed photochemical stability comparable to monomeric fulgides in toluene, <1% per 100 cycles. In general, the properties of the linear and cross-linked copolymers were similar to the corresponding monomers in toluene. In films, the conformations of the Z-form were restricted due to the matrix indicating that the preparation of films from the C-form is advantageous.
Keywords: Photochromism; 3-Indolylfulgimide; Cross-linked copolymer; Thin films;
Structural features and thermal degradation properties of various lignin macromolecules obtained from poplar wood (Populus albaglandulosa) by Jae-Young Kim; Shinyoung Oh; Hyewon Hwang; Ung-Jin Kim; Joon Weon Choi (1671-1678).
Four different lignins obtained from poplar wood (milled wood lignin: ML, organosolv lignin: OL, ionic liquid lignin: IL and Klason lignin: KL) were subjected to several types of chemical/thermal analyses to compare their structural features and thermal decomposition properties. The ML, OL, IL and KL yield from poplar wood was 5.5, 3.9, 5.8, 19.5 wt%, respectively. Functional group analysis revealed that during the OL and KL extraction processes, the condensation reaction involved with phenolic hydroxyl groups of lignins significantly prevailed, which led to a highly condensed OL and KL structure. Thermogravimetric analysis (TGA) results showed that OL and KL thermal stability was much higher than that of ML and IL. The derivatization followed by reductive cleavage (DFRC) data showed that the thermal stability was highly associated with the frequency of arylglycerol-β-aryl ether (β-O-4) linkages in the lignin polymers. Pyrolysis-GC/MS (Py-GC/MS) analysis confirmed that acetic acid and several types of phenolic compounds were the main lignin pyrolysis products. The maximum sum of ML (13.8 wt%), OL (9.9 wt%) and IL (11.8 wt%) pyrolysis products was obtained at the pyrolysis temperature of 600 °C, whereas KL (1.6 wt%) was significantly lower due to its high thermal stability and condensation degree. The S- and G-type pyrolysis products (S/G) ratio varied from 1.61 to 1.93 for ML, 2.28 to 5.28 for OL, 2.06 to 2.86 for IL and 1.40 to 2.20 for KL, depending on the pyrolysis temperature, which ranged between 400 °C and 700 °C.
Keywords: Milled wood lignin; Organosolv lignin; Ionic liquid lignin; Klason lignin; TGA; Py-GC/MS;
Comprehensive on-line HPLC-GC for screening potential migrants from polypropylene into food: The effect of pulsed light decontamination as an example by Roberto Castillo; Maurus Biedermann; Anne-Marie Riquet; Koni Grob (1679-1687).
High performance liquid chromatography (HPLC) was used for the fractionation of extracts from polypropylene (PP) films and coupled on-line to gas chromatography (GC) with automated transfer of the complete HPLC fractions (comprehensive on-line HPLC-GC, i.e. HPLCxGC). Flame ionization detection (FID) was used for the estimation of concentrations, mass spectrometry (MS) for identification work. This method was applied to investigate whether pulsed light (PL) treatment for the microbiological decontamination of polypropylene packaging materials produces reaction products requiring an evaluation to meet regulatory requirements. To demonstrate the safety of PL treatments with regard to the formation of reaction products, i.e. that no component is formed that could endanger human health, basically comprehensive analysis of components potentially migrating into food is required, but comprehensiveness cannot be proven and remains an approximation. The threshold concentration in the film was estimated either from the conventional European non-detection limit of 0.01 mg/kg food or the concept of the threshold of toxicological concern (TTC) for an unknown substance, i.e. an exposure to 0.15 μg per person and day. PL treatment of the films containing Irgafos 168 produced several new components exceeding these limits, i.e. a toxicological safety assessment would probably be required. No such peaks were detected for Tinuvin 326, Irganox 1076 and Chimassorb 81. No degradation of the polymer was detected.
Keywords: Migration from FCM; Comprehensive analysis; On-line HPLC-GC; Irgafos 168; Irganox 1076;
Hydrolytically stable acidic monomers used in two steps self-etch adhesives by Mathieu A. Derbanne; Vincent Besse; Stéphane Le Goff; Michaël Sadoun; Thi-Nhàn Pham (1688-1698).
This study deals with the stability of new phosphonic monomers bearing an acrylamide moiety designed to increase the adhesion durability. Synthesis of monomers bearing acrylamide and methacrylate moieties, as well as their use in Self-Etch Adhesives is reported. The adhesion of a degraded methacrylate based adhesive has been evaluated. Homologous self-etching primers containing monomers bearing acrylamide or methacrylate were formulated and used either immediately after formulation or after 18 months. Their adhesive performances were assessed by shear bond strength testing and their degradation measured by NMR, HPLC-MS. While no differences were found in terms of adhesion between fresh and aged acrylamide based adhesive, the instability of methacrylate based ones was demonstrated. Nevertheless, methacrylate based SEAs still have good adhesion abilities. The co-monomer used, N,N′-diethyl-1,3-bis(acrylamido)propane is expected to be responsible for good mechanical properties even for degraded SEAs. Lastly, the stability of acrylamide monomer seems to be of interest in the prospect of developing SEA with longer shelf life.
Keywords: Acrylamide phosphonic acids; Methacrylate phosphonic acids; Adhesives; Dentin; Dental materials;
Ageing of surface treated thermoplastic polyolefins by Firas Awaja; Michael Gilbert; Minoo Naebe; Georgina Kelly; Bronwyn Fox; Russell Brynolf; Paul J. Pigram (1699-1704).
Thermoplastic polyolefin panels were treated with a flame, flame & water, and accelerated thermo molecular adhesion process (ATmaP) treatment. XPS, contact angle and adhesion test (pull off) results were acquired over a one year period to determine the changes in the elemental composition, surface energy and adhesion strength respectively over time. All surface-treated thermoplastic polyolefin samples showed a sharp decline in adhesion strength up to an ageing period totalling 6 months. The decline in adhesion strength was correlated with a decline in the nitrogen-containing constituents and C–O functional groups at the surface and a decline in surface energy for the flame & water-treated sample. There was no significant change in adhesion strength for all samples for ageing periods greater than 6 months. ATmaP-treated thermoplastic polyolefin outperformed the other two surface treatments in adhesion strength tests due to ATmaP retaining nitrogen-based functional groups (mainly nitrogen oxides) over the year long study. This retention of functionality allowed for a slower ageing process for ATmaP-treated surfaces in comparison to the other surface treatments.
Keywords: Polypropylene; Ageing; XPS; Contact angle; Adhesion;
Monitoring abiotic degradation of branched polyethylenes formulated with pro-oxidants through different mechanical tests by Alejandro Benítez; Johan J. Sánchez; María L. Arnal; Alejandro J. Müller (1705-1716).
The mechanical properties of two linear low density and low density polyethylenes containing a pro-oxidant additive were monitored during accelerated aging (60 °C in a convection oven) and weather exposure. Tearing tests (trouser) were performed for the first time in polyethylenes subjected to oxo-degradation revealing a transition from an extensible to a non-extensible material, at exposure times when standard tensile tests were not able to detect any changes in the materials. The essential work of fracture (EWF) technique was also applied and the results were in agreement with those of trouser tests. The specific essential work of fracture first increased with exposure time until the sample experienced a transition to a less ductile state where EWF was no longer applicable. EWF and trouser tear tests were more sensitive detecting the onset of degradation probably because they employ notched specimens that impose more critical stress concentration conditions than conventional tensile tests.
Keywords: Polyethylene; Degradation; Tear and EWF tests; Double yielding;
Improvement of thermal stability and mechanical properties of medical polyester composites by plasma surface modification of the bioactive glass particles by A. Larrañaga; S. Petisco; J.R. Sarasua (1717-1723).
Poly(l-lactide) (PLLA), poly(ε-caprolactone) (PCL) and poly(l-lactide/ε-caprolactone) (PLCL) are medical (co)polyesters that are conventionally manufactured by thermoplastic processing techniques, such as injection molding or extrusion. However, the addition of bioglass particles causes a degradation reaction of the matrix at high temperatures and could limit the fabrication of composite systems by the above mentioned processes. In this work, a surface modification of bioactive glass particles by plasma polymerization of acrlylic acid is proposed as a strategy for the improvement of thermal stability of bioglass filled composite systems. The developed poly(acrylic acid) layer on the surface of bioglass particles, hinders the degradation reaction between the Si–O− groups present in the surface of the particles and the C＝O groups of the polymer's backbone. As an illustration, the onset degradation temperature (T onset) of PLLA, PCL and PLCL increased respectively from 185.0, 240.1 and 192.2 for bioglass (BG) filled composites to 240.4, 299.5 and 245.7 °C for their modified bioglass (mBG) filled counterparts. Finally, neat PLLA and composites having 15 vol.% of BG and mBG were melt-compounded and subsequently hot pressed to obtain tensile test samples. Non-modified bioglass filled PLLA film was too brittle and difficult to handle due to the sharp reduction of molecular weight during thermoplastic processing. On the contrary, modified bioglass filled PLLA presented a slight increase in Young's modulus with respect to unfilled PLLA but a decrease in both tensile strength and elongation at break.
Keywords: Polylactides; Polylactones; Bioactive glass; Surface modification; Plasma polymerization;
Microbial desulfurization of waste latex rubber with Alicyclobacillus sp. by Chu Yao; Suhe Zhao; Yaqin Wang; Bingwu Wang; Meiling Wei; Minghan Hu (1724-1730).
A microbe with desulfurizing capability, Alicyclobacillus sp., was selected to recycle waste latex rubber (WLR). The growth characteristics of the microorganism and the technical conditions in the co-culture desulfurization process were studied. The desulfurization effect of Alicyclobacillus sp. on the WLR was characterized, and the mechanism for the microbial desulfurization of WLR was tentatively explored. The results showed that adding 5% (w/v) WLR into medium had little effect on the growth of Alicyclobacillus sp. The surfactant polysorbate 80 (Tween 80) had a toxic effect on Alicyclobacillus sp., but the growth of the microbe was vigorous if the proper technique was used: the mixing of WLR with Tween 80, followed by the addition of the mixture into the culture media. With the increase of desulfurization time, the swelling value of desulfurizated waste latex rubber (DWLR) increased, but the crosslink density decreased. After co-culture desulfurization for 8–10 days, a DWLR with good desulfurization effect was obtained. The mechanical properties of natural rubber (NR)/DWLR composite improved significantly over those of NR/WLR composite. XPS and FTIR results revealed that Alicyclobacillus sp. could break the crosslinked sulfur bonds and oxidize them to sulfones groups. The increase of O element content on the surface of DWLR was confirmed by water contact angle measurements. The relationship between the crosslink density and sol fraction of DWLR with different desulfurization times agreed with the Horikx equation, an indication that the microorganisms could break the crosslinked sulfur bonds on the surface of WLR, but leaving the main chains intact.
Keywords: Latex rubber; Alicyclobacillus sp.; Microbial desulfurization; Technical condition; Surface structure; Mechanism;
Synthesis of functionalized α-zirconium phosphate modified with intumescent flame retardant and its application in poly(lactic acid) by Xue-Qi Liu; De-Yi Wang; Xiu-Li Wang; Li Chen; Yu-Zhong Wang (1731-1737).
A novel functionalized α-zirconium phosphate (F-ZrP) modified with intumescent flame retardant was synthesized by co-precipitation method and characterized. Poly (lactic acid) (PLA)/F-ZrP nanocomposites were prepared by melt blending method. The thermal stability and combustion behavior of PLA/F-ZrP nanocomposites were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical burning test (UL-94), scanning electronic microscopy (SEM), and cone calorimeter test (CCT). The results showed that the addition of flame retardant F-ZrP slightly affect PLA's thermal stability, but significantly improve the flame retardancy of PLA composites. In comparison with neat PLA, the LOI value of PLA/F-ZrP was increased from 19.0 to 26.5, and the UL-94 rating was enhanced to V-0 as the loading of F-ZrP at 10%. SEM results suggested the introduction of F-ZrP in the PLA system can form compact intumescent char layer during burning. All these results showed that the F-ZrP performed good flame retardancy for PLA.
Keywords: Poly(lactic acid); Flame retardant; Zirconium phosphate; Cone calorimetry;
Thermal degradation of poly(vinyl chloride)/poly(ethylene oxide) blends: Thermogravimetric analysis by Miće Jakić; Nataša Stipanelov Vrandečić; Ivka Klarić (1738-1743).
Thermal stability of poly(vinyl chloride)/poly(ethylene oxide) (PVC/PEO) blends has been investigated by thermogravimetric analysis (TGA) in dynamic and isothermal heating regime. PVC/PEO blends were prepared by hot-melt extrusion (HME). According to TG analysis, PEO decomposes in one stage, while PVC and PVC/PEO blends in two degradation stages. In order to evaluate the effect of PEO content on the thermal stability of PVC/PEO blends, different criteria were used. It was found that thermal stability of PVC/PEO blends depends on the blend composition. The interactions of blends components with their degradation products were confirmed. By using multiple heating rate kinetics the activation energies of the PVC/PEO blends thermal degradation were calculated by isoconversional integral Flynn–Wall–Ozawa and differential Friedman method. According to dependence of activation energy on degree of conversion the complexity of degradation processes was determined.
Keywords: Activation energy; Poly(ethylene oxide); Poly(vinyl chloride); Polymer blends; Thermal degradation; Thermogravimetric analysis;
Structural evolution and degradation mechanism of Vectran® fibers upon exposure to UV-radiation by Yuxi Liu; Yuyan Liu; Huifeng Tan; Changguo Wang; Huige Wei; Zhanhu Guo (1744-1753).
Vectran® fibers are widely used in military and aerospace industries as high performance fibers. However, they are susceptible to degradation and undergo structural changes when exposed to ultraviolet (UV) irradiation in service. The focus of this work is to investigate the photochemical aging behavior and mechanism of the Vectran® fibers. The morphologies, mechanical properties, chemical structures and behaviors against UV irradiation have been studied. The tensile test results reveal that the tensile strength decreases quickly when the fibers are exposed to Xenon lamp irradiation. The morphology of the Vectran® fiber surface is damaged after accelerated aging. Crystallinity content analysis illustrates that the degree of the fiber structural ordering is decreased due to irradiation. Fourier transformed infrared analyses (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses of the accelerated aged fibers prove the chemical structural changes of the Vectran® fibers. For the first time, the possible photodegradation mechanism of Vectran® fiber is proposed in both air and N2 environments. The rate of degradation and number of chain scissions are greater in air than in N2. The radicals generated by chain scissions can directly abstract a hydrogen atom or can react with O2 creating hydroxyl OH/COOH end groups in air atmosphere. The diaryl ethers may be formed due to the replacement of the H atoms in aromatic rings for linking up two aromatic rings.
Keywords: Fibers; High performance polymers; Photoaging; Photodegradation mechanism; Vectran®;
High photocatalytic degradation activity of polyethylene containing polyacrylamide grafted TiO2 by Wenyao Liang; Ying Luo; Shuangshuang Song; Xianming Dong; Xiaoyuan Yu (1754-1761).
A novel photocatalytic polyacrylamide grafted TiO2 (PAM-g-TiO2) nanocomposite was prepared and embedded into a low density polyethylene (LDPE) plastic. Photocatalytic degradation of the LDPE/PAM-g-TiO2 composite film was carried out under ambient conditions under ultraviolet light irradiation. The properties of composite film were compared with those of the pure LDPE film by measuring the changes in weight loss, carbonyl index, molecular weight, tensile strength and elongation at break. PAM-g-TiO2 embedded LDPE showed highly enhanced photocatalytic degradation. Irradiating the LDPE/PAM-g-TiO2 composite film for 520 h under UV light reduced its weight by 39.85% and average molecular weight (M w) by 94.60%, while that of pure LDPE film was only 1.03% and 69.59%, respectively. The addition of PAM-g-TiO2 brought about the good dispersion of TiO2 in LDPE matrix and improved the hydrophilicity of composite film, which were able to facilitate the degradation of LDPE. The photocatalytic degradation mechanism of the films is briefly discussed.
Keywords: Polyethylene; Polyacrylamide grafted TiO2; Nanocomposite film; Photocatalytic degradation;
Comparison of mechanical properties of heat treated beech wood cured under nitrogen or vacuum by Kévin Candelier; Stéphane Dumarçay; Anélie Pétrissans; Philippe Gérardin; Mathieu Pétrissans (1762-1765).
Heat treated wood has been subjected to increasing interest during the last decade. This non biocidal treatment is an attractive alternative with a low environmental impact to improve decay resistance of low natural durability wood species. Nowadays, several types of heat treatment processes exist. These treatments differ mainly by the nature of the inert atmosphere used to avoid combustion of wood: nitrogen, steam pressure, oil or more recently vacuum. We have shown in a previous study that utilization of vacuum to perform thermal treatment instead of nitrogen allows to reduce considerably degradation of wood polysaccharrides. Indeed, it appears that for a similar 12% mass loss generated by thermal degradation, thermodegradation performed under vacuum allowed to reduce degradation of sugar constitutive of hemicelluloses and formation of recondensation products within the wood structure. These results may be explain by the effect of vacuum allowing removal of volatile degradation products like organic acids, aldehydes and furans limiting therefore acidic degradation of polysaccharides and recondensation of volatile by-products. Decay durability tests, performed against different brown and white rots fungi, have shown no significant differences for vacuum and nitrogen heat treated samples, all presenting an improved decay resistance.According to these results, the aim of this short paper is to report the effect of vacuum versus nitrogen on the mechanical properties of heat treated samples making the assumption that lower degradation of wood polysaccharides during treatment performed under vacuum may reduce the weakening of mechanical properties. For this purpose, modulus of rupture (MOR) and modulus of elasticity (MOE) in bending and Brinell hardness (HB) were determined. Results show that the mechanical properties were lower degraded in the case of wood samples treated under vacuum.
Keywords: Beech; Degradation; Mechanical properties; Nitrogen; Thermal treatment; Vacuum;
The chemical behavior and degradation mitigation effect of cerium oxide nanoparticles in perfluorosulfonic acid polymer electrolyte membranes by Benjamin P. Pearman; Nahid Mohajeri; Darlene K. Slattery; Michael D. Hampton; Sudipta Seal; David A. Cullen (1766-1772).
Perfluorosulfonic acid membranes are susceptible to degradation during hydrogen fuel cell operation due to radical attack on the polymer chains. Mitigation of this attack by cerium-based radical scavengers is an approach that has shown promise. In this work, two formulations of crystalline cerium oxide nanoparticles, with an order of magnitude difference in particle size, are incorporated into said membranes and subjected to proton conductivity measurements and ex-situ durability tests. We found that ceria is reduced to Ce(III) ions in the acidic environment of a heated, humidified membrane which negatively impacts proton conductivity. In liquid and gas Fenton testing, fluoride emission is reduced by an order of magnitude, drastically increasing membrane longevity. Sideproduct analysis demonstrated that in the liquid Fenton test, the main point of attack is weak polymer end groups, while in the gas Fenton test, there is additional side-chain attack. Both mechanisms are mitigated by the addition of the ceria nanoparticles, whereby the extent of the concentration-dependent durability improvement is found to be independent of particle size.
Keywords: Cerium oxide; Perfluorosulfonic acid; Polymer electrolyte membrane (PEM); Fuel cell; Fenton test; Degradation mitigation;
Prevention of oxide aging acceleration by nano-dispersed clay in styrene-butadiene rubber matrix by Shao-Jian He; Yi-Qing Wang; Mei-Mei Xi; Jun Lin; Yang Xue; Li-Qun Zhang (1773-1779).
In order to minimize the oxidative degradation of SBR at high temperature, the nano-dispersed clay layers were introduced by using the SBR/clay (100/80) nanocompound to prepare SBR/clay/carbon black (CB) nanocomposites, then the effects of nano-clay on the properties of SBR nanocomposites are investigated. The clay layers and CB are uniformly dispersed in the SBR matrix at nano-scale. The mechanical properties of the SBR/clay/CB nanocomposites mostly decrease with the increase of clay loading, however, with the increase of clay loading, the change rate of the mechanical properties of the nanocomposites decreases and the aging coefficient of the nanocomposites rises, and the length and depth of the cracks of the aged nanocomposites after bending decrease, which means that the clay layers can provide the nanocomposites excellent thermal aging resistance and heat resistance. The experiment of aging with air and without air proved the importance of oxygen during rubber aging process. The FTIR spectra show the generation of oxygen-containing group on the external surface of the nanocomposites during aging. The DSC results indicate the differences between the internal layer and the external layer of the aged nanocomposites.
Keywords: Clay; SBR; Nanocomposite; High temperature aging; Heat-resisting conveyor belt;
The discovery of free radicals in ancient silk textiles by Decai Gong; Haiyan Yang (1780-1783).
Protection of ancient silk textiles from further deterioration is of vital importance to the investigation and preservation of ancient Chinese culture. Ancient silk textiles from several different ages (more than 2000 years ago) and regions were studied by means of Raman and electron paramagnetic resonance (EPR) spectroscopy in an attempt to unveil the deterioration mechanism of silk. The Raman spectra showed two peaks ( D and G ), which are indicative of carbonization. The EPR spectra of the ancient samples showed a characteristic sharp absorption centered at g∼2.0037 without a hyperfine structure, and have been identified as those of carbon radicals. These free radicals had not been discovered in ancient silk fabrics before, and the discovery may shed light on the deterioration mechanisms of ancient silk textiles.
Keywords: Ancient silk textiles; Raman spectroscopy; EPR spectroscopy; Carbon radicals;
Synthesis of poly(l-lactic acid) with improved thermal stability by sulfonic acid-catalyzed melt/solid polycondensation by Bo Peng; Yutao Xu; Jijiang Hu; Zhiyang Bu; Linbo Wu; Bo-Geng Li (1784-1789).
Melt/solid polycondensation (MP/SSP) is deemed as an alternative synthetic route besides ring-opening polymerization (ROP) in synthesizing poly(l-lactic acid) (PLLA). However, it is found that PLLA synthesized by MP/SSP has much poorer thermal stability than that by ROP due to more residual Sn(II) metallic catalyst in the former, but sulfonic acids does not show any detrimental effect on the thermal stability of PLLA. To synthesizing PLLA with good thermal stability by MP/SSP, a variety of commercially available sulfonic acids were screened as catalysts in MP/SSP of PLLA. Among these nonmetallic catalysts, it was found that 1,3-propanedisulfonic acid (PSA) and 1,5-naphthalene disulfonic acid (NSA) exhibited satisfactory catalytic reactivity and PLLAs with excellent thermal stability, high molecular weight, little coloration and good optical purity were successfully synthesized by MP/SSP. The decomposition temperature was increased by 80–100 °C in comparison to SnCl2-catalyzed PLLA, and the thermal stability is comparable to commercial PLLA produced by ROP.Display Omitted
Keywords: Biodegradable polymers; Biobased polymers; Poly(l-lactic acid); Polycondensation; Thermal stability; Nonmetallic catalyst;
Hydrolyzable and bio-based polyester/nano-hydroxyapatite nanocomposites: Structure and properties by Weifu Dong; Jingjiao Ren; Dongjian Shi; Piming Ma; Xiao Li; Fang Duan; Zhongbin Ni; Mingqing Chen (1790-1795).
Hydrolyzable and bio-based poly(DHCA-co-HDA) (PDH)/nano-hydroxyapatite (n-HA) nanocomposites were fabricated by polycondensation of 3,4-dihydroxycinnamic acid (DHCA) and 10-hydroxydecanoic acid (HDA) with various amount of n-HA. The structure of nanocomposites was characterized by FT-IR. DSC results indicated that the T gs of the nanocomposites were improved with increasing n-HA content. The SEM micromorphology revealed that n-HA nano-particles were well dispersed in PDH, which was due to the good compatibility between n-HA and PDH. With addition of n-HA in PDH, the tensile strength of nanocomposites prominently enhanced, however the elongation at break reduced. The presence of n-HA increased the hydrophilicity and hydrolysis rate of PDH/n-HA nanocomposites. Moreover, the hydrophilicity and degradation rate of nanocomposites can be altered through varying the content of n-HA.
Keywords: Hydrolysable polyester; Hydroxyapatite; Nanocomposites; Hydrolysis rate;
Effects of composition and sequential structure on thermal properties for copolymer of 3-hydroxybutyrate and lactate units by Yuta Tabata; Hideki Abe (1796-1803).
Copolymers of (R)-3-hydroxybutyrate (3HB) and (R)-lactate ((R)-2-hydroxypropionate: 2HP) units were synthesized by polycondensation reaction from methyl esters of 3HB and 2HP in the presence of titanium-based catalyst. Mixing of two monomers from the beginning of polymerization yielded random copolymers of 3HB and 2HP units. On the other hand, by controlling the time of mixing of two monomers, copolymers with blocking tendency were obtained. The structure and thermal properties of the obtained copolymers were characterized by 1H and 13C NMR, X-ray diffraction, differential scanning calorimetry, and optical microscopy. Glass-transition temperature of the copolymers was mainly governed by the copolymer composition, and the values varied linearly with the composition. In contrast, the melting temperature was strongly depending on the sequential length of crystallizable monomeric unit, and the values were in inverse proportion to the number-averaged sequential length of crystallizable monomeric unit. The crystallinity of the copolymer samples was affected by both the composition and sequential length of crystallizable monomeric unit. The finding is valuable for design of copolymer molecules with desirable thermal properties by controlling both the copolymer composition and sequential structure.
Keywords: Copolymer of 3-hydroxybutyrate and lactate; Thermal properties; Sequential structure; Blocking tendency;
The water vapour adsorption–desorption behaviour of naturally aged Tilia cordata Mill. wood by Carmen-Mihaela Popescu; Callum A.S. Hill (1804-1813).
The effect caused by the natural ageing of wood on the sorption properties during two consecutive sorption cycles of historical Tilia cordata Mill. wood has been investigated and compared with a reference sample. Differences were found in the sorption isotherm between the first and second sorption cycles for most of the samples and also between the reference and historical wood.All samples exhibited sorption hysteresis, but with important differences in behaviour observed with the historic wood samples. It was interesting to note that the oldest historic wood sample did not display any discernible difference between the first and second sorption cycle throughout much of the hygroscopic range and also exhibited absolute hysteresis values essentially identical with the reference sample. These results indicate that the sorption behaviour of wood is dependent upon the previous exposure of the wood to atmospheric relative humidity. The sorption kinetics was also analysed in terms of the parallel exponential kinetics (PEK) model, and excellent fits to the data were obtained. The PEK model describes the dynamic sorption behaviour in terms of a fast and slow kinetic process and important differences in behaviour for these two processes were found. It is thought that the fast process is associated with a physical diffusion phenomenon, while the slow kinetics process is considered to be associated with cell wall matrix polymer relaxation processes.
Keywords: Dynamic water vapour sorption; Tilia cordata wood; Parallel exponential kinetic (PEK) model; Sorption isotherm;
Degradation and cis-to-trans isomerization of poly[(2,4-difluorophenyl)acetylene]s of various initial molecular weight: SEC, NMR, DLS and EPR study by Olga Trhlíková; Jiří Zedník; Pavel Matějíček; Michal Horáček; Jan Sedláček (1814-1826).
Molecular weight (MW) and configurational stabilities of a series of high-cis poly[(2,4-difluorophenyl)acetylene]s (PdFPhA, M w from 2.2 × 104 to 9.7 × 105) exposed to the atmosphere and diffuse daylight are reported. Polymers dissolved in THF-d 8 undergo simultaneous cis-to-trans isomerization and degradation under formation of a bimodal MW distribution. Degradation and isomerization rates are tightly connected and decrease with decreasing MW of the parent PdFPhAs. This finding may be interesting for the functional applications of substituted polyacetylenes. The partly aged PdFPhAs contain two separable fractions: higher-MW high-cis macromolecules containing a low amount of unpaired electrons and lower-MW deeply isomerized cis/trans macromolecules enriched in the unpaired electrons content. The difference in MW of these fractions reflects the various degradation rates of isomerized and high-cis macromolecules. Only a slow degradation without changes in the configurational structure proceeds if PdFPhA is allowed to age in the solid state. The suppression of the cis-to-trans isomerization reflects the suppression of motion of the polymer chains segments in the solid state.
Keywords: Conjugated polymers; Polyacetylenes; Degradation; Isomer/isomerization; 1,3,5-Tris(2,4-difluorophenyl)benzene; GPC;
The impact of volatile compounds released by paper on cellulose degradation in ambient hygrothermal conditions by J. Tétreault; A.-L. Dupont; P. Bégin; S. Paris (1827-1837).
The reactivity towards cellulose of various volatile compounds commonly released by paper was studied. Sheets of Whatman No. 1 (W1) and No. 40 (W40) were exposed to various concentrations of these compounds in vapour phase ranging from 20 to 80 ppm in closed vessels for 52 days in controlled ambient conditions, after which they were hygrothermally aged. The measured properties of the paper were copper number, degree of polymerization, zero-span breaking length, pH and yellowness index. The results showed that hydrogen peroxide was the most aggressive among the volatile compounds tested as it severely degraded W1 cellulose. The exposure of W1 to formic acid led to significant degradation, designating this volatile organic compound (VOC) as the most reactive toward cellulose among the carboxyl and carbonyl functionalized VOCs tested. On the other hand, acetic acid was found comparatively less reactive. Nitrogen oxides, which were produced up to 3 ppm from a side-reaction of the carboxylic acids with the magnesium nitrate used to control the relative humidity in the closed vessels, appeared to contribute significantly to the degradation despite their low concentration. Antagonistic effects were evidenced in binary vapour mixtures where the presence of aldehydes (formaldehyde and acetaldehyde) counteracted substantially the degradation induced by the most reactive compounds. It was also shown that acetaldehyde, hexanal and furfural in individual exposures had little to no reactivity. Upon exposure to formaldehyde, the rate of glycosidic bond cleavage of cellulose induced by the ageing of W1 was significantly reduced.
Keywords: Degree of polymerization; Formaldehyde; Formic acid; Hydrogen peroxide; Oxidation; VOC;
Thermal and combustion behavior of polyethersulfone-boehmite nanocomposites by Marco Monti; Giovanni Camino (1838-1846).
In this paper, we report a thorough study on the thermal stability and fire behavior of polyethersulfone (PES) filled with 2 wt% nano-sized aluminum oxide hydroxide particles (boehmite). The nanocomposite was prepared through melt compounding technique in a co-rotating twin screw extruder. The obtained morphology of the composite was studied by scanning electron microscopy (SEM) coupled with elemental analysis, proving that an even distribution of sub-micron boehmite particles was obtained. PES shear modulus, measured by DMA, is increased by 30% in the boehmite nanocomposite. Thermal stability of the produced materials was studied through thermal gravimetric analysis (TGA), whereas the combustion behavior through cone calorimeter and vertical burning (UL-94) tests. Cone calorimeter results show that a significant overall flame retardant effect was observed due to the presence of boehmite nanoparticles, which could not be detected by UL-94 fire scenario where neat PES is already top ranked V0.
Keywords: Polyethersulfone; Boehmite; Flame retardancy; Thermal degradation; Cone calorimeter;
Biodegradability of nylon 4 film in a marine environment by Koichiro Tachibana; Yuichi Urano; Keiji Numata (1847-1851).
Biodegradability of nylon 4 in seawater from Tokyo Bay was investigated by weight loss and biochemical oxygen demand (BOD) of nylon 4 films. The remaining weight of nylon 4 film decreased with incubation time in the seawater, and the percentage of weight loss of nylon 4 film was 30% after 3 weeks. BOD biodegradability of nylon 4 film was approximately 80% within 25 days. Scanning electron microscopy images of the nylon 4 film before and after the seawater treatment revealed that the surface of the nylon 4 films was eroded after biodegradation in seawater. The average molecular weights of the nylon 4 films indicated no significant difference between before and after 30% weight loss of the film. Based on the present data, nylon 4 film was degraded on the surface of the film in the seawater. Furthermore, microbial degradation seemed to be one of the main degradation mechanisms of nylon 4.
Keywords: Nylon 4; Biodegradation; Marine environment; Bioplastic;
Photochromic switchable pendant indolyl fulgimide polypyrrole by Nithyanandan Sivasankaran; Kannan Palaninathan (1852-1861).
The photochromic switchable 2-indolyl fulgimide functionalized pyrrole monomer is synthesized and ascertained by spectroscopic techniques. The absorption and emission band of monomer due to intramolecular charge transfer (ICT) state exhibit typical bathochromic shift from nonpolar to polar solvents. The molecular geometry and bandgap energy of monomer in open form as well as closed form are calculated by B3LYP/6-31 G (d) with Gaussian 03 program package. The functionalized pyrrole monomer is electropolymerized by cyclicvoltammetric method on an electrode. The polymer indicated a completely reversible photoswitching between two isomers of open and closed form 2-indolyl fulgimide moiety, which are stable over many cycles of operation by UV/visible light sources. The closed form of polymer exhibit fluorescence quenching attributed to the energy transfer from conductance band of polypyrrole to closed form of 2-indolyl fulgimides unit. This fluorescence quenching system controls the conductance of conducting polymer in molecular electronics and molecular switches.Display Omitted
Keywords: Electropolymerization; Photochromism; 2-indolyl fulgimide; Polypyrrole; Optical switching; Electron transfer;
Thermal and photochemical effects on the structure, morphology, thermal and optical properties of PVA/Ni0.04Zn0.96O and PVA/Fe0.03Zn0.97O nanocomposite films by D.M. Fernandes; J.L. Andrade; M.K. Lima; M.F. Silva; L.H.C. Andrade; S.M. Lima; A.A. Winkler Hechenleitner; E.A. Gómez Pineda (1862-1868).
Ni0.04Zn0.96O and Fe0.03Zn0.97O with average diameter of 23 and 19 nm, respectively, have been synthesized by a modified sol–gel method to be used in the preparation of (100 − x)/x poly(vinyl alcohol)/oxide nanocomposite films, with x = 0, 1, 3 and 5 (in wt.%). A 125 W-Hg vapor lamp with emission above 254 nmwas used to irradiate PVA/Ni0.04Zn0.96O and PVA/Fe0.03Zn0.97O films. The effect on their structural, thermal, morphological and optical properties was studied by TG, DSC, DRX, AFM, UV–vis and PL spectrophotometry. The Ni0.04Zn0.96O addition on PVA films decreases the thermal stability of the polymer in inert and in oxidative atmosphere. In contrast, the Fe0.03Zn0.97O presence in the PVA films seems to increase the thermal stability of the polymer. The characteristic peak of the crystalline phase of PVA and wurtzite phase of the zinc oxide were identified through X-ray diffraction in both films. The crystallinity of the PVA film increases with UV irradiation and with the presence of Ni0.04Zn0.96O and Fe0.03Zn0.97O. The roughness of the PVA film was not modified by the addition of the doped oxides; however, it increases after UV irradiation, more significantly in the films containing the oxides. The PVA film exhibits absorption around 280 nm characteristic of π–π∗ transitions related to carbonyl groups from residuals acetate, while the 95/05 PVA/Ni0.04Zn0.96O and 95/05 PVA/Fe0.03Zn0.97O nanocomposite films show absorption at the visible region which is characteristics of the band gap reduction of the doped oxides. The photoluminescence of PVA was modified by the presence of the oxides in the film. These nanocomposite films are interesting due to their thermal, mechanical (flexible) properties and low cost of production. In addition they are also able to exhibit peculiar optical properties showing potential to be used in photonic devices, gas sensors and organic solar cell applications.
Keywords: Optical properties; Ni0.04Zn0.96O; Fe0.03Zn0.97O; PVA; Nanocomposite films;
Thermal stabilization of poly(hexamethylene adipamide) fibers in the presence of ferric chloride prior to carbonization by Ismail Karacan; Kemal Şahin Tunçel (1869-1881).
Thermal stabilization of poly(hexamethylene adipamide) (polyamide 66, PA66) fibers in the presence of ferric chloride was performed in air at 215 °C for stabilization times ranging from 15 min to 6 h. The presence of ferric ions in the PA66 structure enhanced thermal stabilization reactions. Optical microscopy, density, elemental analysis, X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and infrared (IR) spectroscopy measurements were used to examine and characterize the structural transformations occurring during the thermal stabilization. Ferric chloride (FeCl3) pretreatment followed by thermal stabilization in an air atmosphere resulted in major physical and structural transformations. Physical transformations were revealed as a reduction in fiber diameter and an increase in density values together with major color changes. Ferric chloride pretreated and thermally stabilized PA66 fibers were found to be fully stabilized after 6 h of stabilization and acquired infusible and nonburning characteristics prior to the carbonization stage. Elemental analysis showed a reduction in carbon, nitrogen and hydrogen contents. The DSC and TGA measurements demonstrated that there was an improvement in the thermal stability. The TGA thermograms showed a relative improvement in thermal stability as indicated by increasing char yield with progressing time. The char yield reached a maximum value of 40% at 1000 °C for the ferric chloride pretreated PA66 fibers stabilized for 6 h at 215 °C. Experimental results obtained from the DSC, X-ray diffraction and infrared spectroscopy methods indicated gradual and continuous disordering reactions as a result of the scission of the hydrogen bonds with progressing time. The IR measurements also indicated the formation of the carbonyl (C＝O) group as a result of oxidative crosslinking reactions and the occurrence of dehydrogenation reactions caused by the loss of hydrogens from the methylene (CH2) groups in agreement with the elemental analysis. Sample preparation appeared to play an important role in the formation of ferric ion coordination bonds with the carbonyl oxygen atoms. The unconstrained stabilization method caused an enhancement of the complexation of ferric ions with the amide groups. A new method of evaluating the X-ray stabilization index was devised specifically for the thermally stabilized PA66 fiber.
Keywords: Thermal stabilization; Polyamide 66; Elemental analysis; Thermal analysis; X-ray diffraction; Infrared spectroscopy;
Synthesis and biodegradation of poly(2-pyrrolidone-co-ε-caprolactone)s by Atsuyoshi Nakayama; Naoko Yamano; Norioki Kawasaki; Yasuhide Nakayama (1882-1888).
Copolyesteramides of 2-pyrrolidone with ε-caprolactone were synthesized by ring-opening copolymerization. The copolymers were random-like and their melting temperature and heat of fusion were dependent on the polymer composition. Biodegradation by a polyamide 4 (PA4) degrading microorganism showed rapid degradation in the region of amide-rich polymer composition. On the contrary, enzymatic hydrolysis using a lipase resulted in a different tendency, that is, ester-rich copolymers hydrolyzed rapidly. Activated sludge makes copolymers degrade to CO2 in wide polymer composition ratio. Copolyesteramides are expected to be applied as an environmentally-friendly plastics or bioabsorbable polymers in medical fields.
Keywords: Biodegradable; Biobased; Polyamide 4; Activated sludge; Hydrolysis;
Thermal behaviour of binary and ternary copolymers containing acrylonitrile by Bogdanel Silvestru Munteanu; Mihai Brebu; Cornelia Vasile (1889-1897).
Keywords: Copolymers; Thermogravimetry; Pyrolysis; Styrene; Acrylonitrile;
Sustainability assessments of bio-based polymers by Troy A. Hottle; Melissa M. Bilec; Amy E. Landis (1898-1907).
Bio-based polymers have become feasible alternatives to traditional petroleum-based plastics. However, the factors that influence the sustainability of bio-based polymers are often unclear. This paper reviews published life cycle assessments (LCAs) and commonly used LCA databases that quantify the environmental sustainability of bio-based polymers and summarizes the range of findings reported within the literature. LCA is discussed as a means for quantifying environmental impacts for a product from its cradle, or raw materials extraction, to the grave, or end of life. The results of LCAs from existing databases as well as peer-reviewed literature allow for the comparison of environmental impacts. This review compares standard database results for three bio-based polymers, polylactic acid (PLA), polyhydroxyalkanoate (PHA), and thermoplastic starch (TPS) with five common petroleum derived polymers. The literature showed that biopolymers, coming out of a relatively new industry, exhibit similar impacts compared to petroleum-based plastics. The studies reviewed herein focused mainly on global warming potential (GWP) and fossil resource depletion while largely ignoring other environmental impacts, some of which result in environmental tradeoffs. The studies reviewed also varied greatly in the scope of their assessment. Studies that included the end of life (EOL) reported much higher GWP results than those that limited the scope to resin or granule production. Including EOL in the LCA provides more comprehensive results for biopolymers, but simultaneously introduces greater amounts of uncertainty and variability. Little life-cycle data is available on the impacts of different manners of disposal, thus it will be critical for future sustainability assessments of biopolymers to include accurate end of life impacts.
Keywords: Biopolymer; Environmental impacts; Life cycle assessment (LCA); Polylactic acid (PLA); Polyhydroxyalkanoate (PHA); Thermoplastic starch (TPS);
Nanocomposites of aliphatic polyesters: An overview of the effect of different nanofillers on enzymatic hydrolysis and biodegradation of polyesters by Dimitrios N. Bikiaris (1908-1928).
In the present review the findings concerning the effect of nanofillers to biodegradation and enzymatic hydrolysis of aliphatic polyesters were summarized and discussed. Most of the published works are dealing with the effect of layered silicates such as montmorillonite (unmodified and modified with organic compounds), carbon nanotubes and spherical shape additives like SiO2 and TiO2. The degradation of polyester due to the enzymatic hydrolysis is a complex process involving different phenomena, namely, water absorption from the polyesters, enzymatic attack to the polyester surface, ester cleavage, formation of oligomer fragments due to endo- or exo-type hydrolysis, solubilization of oligomer fragments in the surrounding environment, diffusion of soluble oligomers by bacteria and finally consumption of the oligomers and formation of CO2 and H2O. By studying the published works in nanocomposites, different and sometimes contradictory results have been reported concerning the effect of the nanofillers on aliphatic polyesters biodegradation. Most of the papers suggested that the addition of nanofillers provokes a substantial enhancement of polyester hydrolysis due to the catalyzing effect of the existed reactive groups (–OH and –COOH), to the crystallinity decrease, to the higher hydrophilicity of nanofillers and thus higher water uptake, to the higher interactions, etc. However, there are also some papers that suggested a delay effect of nanofillers to the polyesters degradation mainly due to the barrier effect of nanofillers and the lower available surface for enzymatic hydrolysis.
Keywords: Aliphatic polyesters; Nanocomposites; Nanofillers; Enzymatic hydrolysis; Biodegradation;
Review: Auto-oxidation of aliphatic polyamides by Emmanuel Richaud; Octavie Okamba Diogo; Bruno Fayolle; Jacques Verdu; Jean Guilment; François Fernagut (1929-1939).
The literature on oxidation kinetics of polyamides and model compounds has been reviewed in order to try to extract suitable information for non-empirical kinetic modeling. Polyamide characteristics are systematically compared to polyolefin ones, these latter being more extensively studied. From kinetic analysis point of view, it is shown that oxidation attacks predominantly α amino methylenes of which C–H bond is considerably weaker than the other methylenes. As a result, propagation by H abstraction is considerably faster in polyamides than in polyethylene for instance. Termination by radical combination is also very fast. Another cause of PA oxidizability is the instability of α amino hydroperoxides linked to the inductive effect of nitrogen. This instability is responsible for many key features of oxidation kinetics especially the absence of induction period.The main stable oxidation products are imides resulting from disproportionation processes meanwhile chain scissions resulting from rearrangements of α amino alkyls by β-scission are also significant process although their yield appears lower than in polyolefins.
Keywords: Aliphatic polyamides; Oxidation; Mechanisms; Kinetics; Oxidation products;
Fabrication of nano-crystalline cellulose with phosphoric acid and its full application in a modified polyurethane foam by Shujun Li; Chunjie Li; Changyu Li; Meiling Yan; Yanjiao Wu; Jianbo Cao; Sanchun He (1940-1944).
Nano-crystalline cellulose was fabricated in an anhydrous phosphoric acid system with medical absorbent cotton as its raw material. After ammonia neutralization, the whole system with produced phosphates and hydrolyzed saccharides was used as a modifier for preparing polyurethane foam (PUF). The NCC worked as a reinforce material, the phosphates served as flame-retardants, and the hydrolyzed saccharides partly replaced polyol. The addition of the modifier significantly improved mechanical property and flame-retardancy without an inferior thermal conductivity. When the dosage of modifier was 6% of the whole polyol, compressive strength increased 4.29 times, heat release rate dropped to 50.7%, and time to ignition extended to 2.6 times of those of the neat PUF. XRD and TEM analyses proved that the NCC in the modifier was rod-shape cellulose Ⅱ with diameter of 10 nm or so. FTIR analysis confirmed that the modifier well reacted with isocyanate, and SEM results revealed that the flame-retardant PUF had more uniform cells and more regular skeleton structure than the neat PUF.
Keywords: Nano-crystalline cellulose; Phosphoric acid; Polyurethane foam (PUF); Modification; Flame retardant;
Antioxidant behavior of a novel sulfur-bearing hindered phenolic antioxidant with a high molecular weight in polypropylene by Xiaofeng Wang; Bibo Wang; Lei Song; Panyue Wen; Gang Tang; Yuan Hu (1945-1951).
A novel sulfur-bearing hindered phenolic antioxidant with a molecular weight of 1305.9 (SAO) was successfully synthesized via thiol-acrylate Michael addition reaction and its structure was clarified by nuclear magnetic resonance (NMR) and fourier transform infrared spectra (FTIR). The short-term oxidation induction time (OIT) of polypropylene (PP) compounds obtained at 210 °C showed that the OIT value of SAO-containing PP was higher than that of PP using Chinox 1035 with a molecular weight of 642.9 as a stabilizer. Long-term accelerated thermal aging test of PP compounds in an air oven at 150 °C, however, exhibited that the aging resistance of SAO-stabilizing PP was inferior to that of 1035-containing PP, quite contrary to their respective short-term effect on PP stabilization. The possible reasons of this contradiction were discussed from the viewpoint of the antioxidants' molecular structure and the limitations of the OIT approach in lifetime prediction.
Keywords: Sulfur-bearing hindered phenolic antioxidant; Polypropylene; Antioxidant behavior; Antioxidant degradation;