Polymer Degradation and Stability (v.94, #4)
Flame retardancy of silicone-based materials by Siska Hamdani; Claire Longuet; Didier Perrin; José-Marie Lopez-cuesta; François Ganachaud (465-495).
This review describes some recent works related to the development of the flame retardation of silicone elastomers and/or applications of silicones as flame retardant agents in other polymers. First, the thermal degradation of silicones themselves is discussed, focussing on depolymerization mechanisms, effect of structure, heating conditions, and effect of additives (i.e. less than 5 wt% fillers) on thermal degradation of silicones. Then, the influence of several types of mineral fillers (of up to 80 wt% content) as ceramization agents of silicones is presented. Finally, the introduction of (functionalized) silicones as flame retardants into other polymers is described.
Keywords: Flame retardancy; Silicone; Mineral fillers; Ceramization;
Variation of benzyl anions in MgAl-layered double hydroxides: Fire and thermal properties in PMMA by Calistor Nyambo; Dan Chen; Shengpei Su; Charles A. Wilkie (496-505).
Magnesium aluminum layered double hydroxides (MgAl-LDHs) intercalated with a range of benzyl anions were prepared using the coprecipitation method. The benzyl anions differ in functionality (i.e. carboxylate, sulfonate, and phosphonate) and presence or absence of an amino substituent. Various methods for preparing LDHs (i.e. ion exchange, coprecipitation and rehydration of the calcined LDH methods) have been compared with the MgAl-benzene phosphonate and their effect on fire and thermal properties was studied. After characterization, the MgAl-LDHs were melt-blended with poly(methyl methacrylate) (PMMA) at loadings of 3 and 10% by weight to prepare composites. Characterization of the LDHs and the PMMA composites was performed using FTIR, XRD, TGA, transmission electron microscopy (TEM) and cone calorimetry. FTIR and XRD analyses confirmed the presence of the charge balancing benzyl anions in the galleries of the MgAl-LDHs. Improvements in fire and thermal properties of the PMMA composites were observed. The cone calorimeter revealed that the addition of 10% MgAl-LDHs reduces the peak heat release rate by more than 30%.
Keywords: Poly(methyl methacrylate); Layered double hydroxide; Thermogravimetry; Cone calorimeter; Fire retardancy;
Layered double hydroxides intercalated with borate anions: Fire and thermal properties in ethylene vinyl acetate copolymer by Calistor Nyambo; Charles A. Wilkie (506-512).
Fire and thermal properties of ethylene vinyl acetate (EVA) composites prepared by melt blending with layered double hydroxides (LDH) have been studied. Two types of LDHs intercalated with borate anion were prepared using the coprecipitation method and the metals Mg2+, Zn2+ and Al3+. Characterization of the LDHs and the EVA composites was performed using X-ray diffraction, thermogravimetric analysis, and cone calorimetry. Thermal analyses show that the addition of LDHs improves the thermal stability of EVA. Fire properties evaluated using the cone calorimeter were significantly improved in the EVA/LDH composites. The peak heat release rate was reduced by about 40% when only 3% by weight of the LDH was added to the copolymer. Comparison of the fire properties of the LDHs with those of aluminum trihydrate (ATH), magnesium hydroxides (MDH), zinc hydroxide (ZH) and their combinations at 40% loading, reveal that the LDHs were more effective than when MDH and ZH are used alone.
Keywords: Ethylene vinyl acetate; Layered double hydroxide; Borate; Thermogravimetry; Fire retardancy; Cone calorimeter;
Thermal stability and flammability characteristics of ethylene vinyl acetate (EVA) composites blended with a phenyl phosphonate-intercalated layered double hydroxide (LDH), melamine polyphosphate and/or boric acid by Calistor Nyambo; Everson Kandare; Charles A. Wilkie (513-520).
A phenyl phosphonate-intercalated MgAl–LDH (MgAl–PPh), melamine polyphosphate (MP), and boric acid (BA) were independently and concomitantly added to neat ethylene vinyl acetate (EVA) copolymer at loading fractions of 10% (w/w). The structural morphology of MgAl–PPh was established via powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM) while the presence of phenyl phosphonate in the galleries was confirmed by Fourier transform infrared (FTIR). Thermogravimetric analysis (TGA) and cone calorimetry were used to evaluate the thermal stability and flammability behavior of EVA and its composites. While time-to-ignition is greatly reduced for EVA composites compared to the virgin polymer, there are remarkable reductions in the peak heat release rate (PHRR) which relates to a reduction in flame intensity. Synergistic effects were observed in cone calorimetry for the formulation containing MgAl–PPh, MP, and BA.
Keywords: EVA; Layered double hydroxide; Melamine polyphosphate; Boric acid; Synergy;
Gel production, oxidative degradation and dielectric properties of isotactic polypropylene irradiated under various atmospheres by E. Suljovrujic (521-526).
In this work, changes in structure and physical properties of stabilized isotactic polypropylene (iPP) were created by gamma irradiation, up to a dose of 700 kGy, in different media: air, deionised distilled (DD) water and acetylene. Gel and infrared (IR) spectroscopy measurements were used to determine the changes in the degree of network formation and oxidative degradation, respectively. Sol–gel analysis was studied in detail using the Charlesby–Pinner (C–P) equation. The radiation-induced changes in the structure and evolution of oxygen-containing species were also studied through dielectric loss (tan δ) analysis in a wide temperature and/or frequency range. Evolution of low temperature dielectric relaxations with gamma irradiation was investigated. In the case of dielectric relaxation measurements, the polar groups that were introduced by irradiation in non-polar iPP were considered as tracer groups. Conclusions derived according to different methods were compared.
Keywords: Gamma irradiation; Polypropylene; Cross-linking; Oxidative degradation; Dielectric properties;
Influence of melt behaviour on the flame retardant properties of ethylene copolymers modified with calcium carbonate and silicone elastomer by Linus Karlsson; Anna Lundgren; Jonas Jungqvist; Thomas Hjertberg (527-532).
This work describes a halogen-free flame retardant material consisting of a polar ethylene copolymer, calcium carbonate and silicone elastomer. The flame retardant properties when using poly(ethylene-co-methacrylic acid) (EMAA) and poly(ethylene-co-butyl acrylate) (EBA) as the copolymer have been compared. Rheological measurements showed an increase in complex viscosity above 250 °C due to ionomer formation between acidic groups in the polymer and calcium ions. The increase in viscosity occurs at lower temperatures with the EMAA material and the increase is stronger. This has great impact on the fire performance, as shown with cone calorimetry and dripping test. In order to further elucidate the flame retardant mechanism in detail, thermogravimetric analysis and infrared spectroscopy have been used. The influence of the amount of comonomer and melt flow ratio of the polymer is also commented.
Keywords: Melt behaviour; Viscosity; Flame retardant; EBA; EMAA; Calcium carbonate;
Activities of octoate salts as novel catalysts for the transesterification of flexible polyurethane foams with diethylene glycol by C. Molero; A. de Lucas; J.F. Rodríguez (533-539).
Polyurethane foams are disposed of not only at the end of their use but also as scrap during slabstock manufacturing, leading to an environmental and economic problem. Flexible polyurethane foams can be advantageously treated by two-phase glycolysis in order to recover their constituent polyols with an improved quality compared to the single phase processes. The glycolysis comprises a transesterification, which has been traditionally catalyzed by alkanolamines, titanium compounds and acetates. In this work, the performance evaluation of new catalysts based on alkaline, alkaline-earth and transition metal octoate salts has been carried out. The carboxylates have showed different catalytic activities according to their basicity and coordination ability. A reaction mechanism for the polyurethane glycolysis in the presence of the carboxylate catalysts studied has also been proposed. The mechanism involves several steps, including the formation of a metal alkoxylate, coordination–insertion of the alkoxide into the urethane group and transfer from recovered polyol to glycol. Among the octoates studied, lithium and stannous octoates showed a remarkable catalytic activity. They yielded the greatest quality for the recovered polyol as well as the highest decomposition rates.
Keywords: Polyurethane; Transesterification; Catalysts; Glycolysis;
Thermal degradation behaviour of poly(vinyl chloride) in the presence of poly(N′-acryloyl benzhydrazide) by Nadia Ahmed Mohamed; Noura Yahya Al-mehbad (540-543).
The thermal degradation behaviour of poly(vinyl chloride), PVC, in the presence of poly(N′-acryloyl benzhydrazide), PABH, has been studied using continuous potentiometric determination of the evolved hydrogen chloride gas from the degradation and by measuring the extent of discoloration of the degraded samples. Blending this polymeric additive with dibasic lead carbonate, DBLC, reference stabilizer in different ratios had synergistic effects on both the thermal stability and the extent of discoloration of PVC.
Keywords: Poly(vinyl chloride); Poly(N′-acryloyl benzhydrazide); Thermal dehydrochlorination; Discoloration; Co-stabilizer;
Preparation and characterisation of a novel fire retardant PET/α-zirconium phosphate nanocomposite by De-Yi Wang; Xue-Qi Liu; Jun-Sheng Wang; Yu-Zhong Wang; Anna A. Stec; T. Richard Hull (544-549).
The preparation of a novel fire retardant nanocomposite of poly(ethylene terephthalate) (PET) using nanoscopic α-zirconium phosphate (α-ZrP), by in situ polymerisation was investigated. The novel fire retarded PET nanocomposite, PET-co-DDP/α-ZrP, was synthesized by the direct condensation of terephthalic acid, ethylene glycol, 9,10-dihydro-10[2,3-di(hydroxycarbonyl)propyl]-10-phosphaphenanthrene-10-oxide (DDP) and nano α-ZrP. The morphology, thermal stability and burning behaviour of the nanocomposite with 1 wt% α-ZrP loading was investigated. The extent of dispersion of the nanofillers was quantified by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Significant improvements in fire retardant performance were observed for the nanocomposite from limiting oxygen index (increased from 21.2 to 32.6), UL-94 (achieving V-0), and cone calorimetry (reducing both the heat release rate and the total heat released, without reducing the time to ignition).
Keywords: Fire retardant; Flame retarded; Poly(ethylene terephthalate); PET; In situ polymerisation; Nanocomposite;
Fabrication, morphology and thermal degradation behaviors of conductive polyaniline coated monodispersed polystyrene particles by Erh-Chiang Chen; Yen-Wen Lin; Tzong-Ming Wu (550-557).
This study describes the preparation of polyaniline (PANI) coated on the surface of monodispersed 400 nm polystyrene (PS) particles by in situ chemical oxidative polymerization. The monodispersed 400 nm PS particles served as cores were synthesized using the emulsion polymerization. Both images observed by field-emission scanning electron microscopy and transmission electron microscopy show the presence of a thin PANI layer uniformly coated on the surface of PS particle. The electrical conductivity of various amounts of PANI-coated PS particles is significantly increased about 13 orders of magnitude compared to that of the pristine PS particles. Differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) were used to investigate the thermal stability and thermal degradation behavior of PS and PANI-coated PS particles. Both DSC and TGA curves revealed that the coating of a thin PANI layer on the surface of PS can drastically increase the thermal stability of PS matrix. TGA isothermal degradation data illustrate that the activation energy of the PANI-coated PS particle is larger than that of PS. This phenomenon can be attributed to the incorporation of PANI coating on the surface of PS particle caused a decrease in the degradation rate and an increase in the residual weight for the PANI-coated PS particle.
Keywords: Polystyrene; Polyaniline; Emulsion polymerization; Thermal degradation kinetics; Activation energy;
The effect of phosphorus content on the thermal and the burning properties of cotton fabric coated with an ultrathin film of a phosphorus-containing polymer by Ampornphan Siriviriyanun; Edgar A. O'Rear; Nantaya Yanumet (558-565).
The effect of phosphorus content on thermal degradation and burning behavior of poly(acryloyloxyethyl diethyl phosphate) or PADEP-coated cotton was studied. The results showed that PADEP-coated cotton prepared by admicellar polymerization using hexadecyltrimethylammonium bromide (HTAB) as a surfactant has higher amounts of phosphorus than that prepared using dodecyltrimethylammonium bromide (DTAB). Higher phosphorus content led to lower decomposition temperatures and greater amounts of char formation after thermal degradation. The effectiveness of the amount of phosphorus on the burning behavior of the treated cotton was investigated by an ASTM flammabilty test. In the case of PADEP-coated cotton prepared with DTAB, the flame spread slowly and extinguished with char formation on the fabric. For untreated cotton however, the flame spread quickly and burned the fabric entirely without char formation. Cotton coated with PADEP using HTAB exhibited self-extinguishing behavior after removing the ignition source. Decrease in decomposition temperature, increase in char formation and the burning behavior of PADEP-coated cotton are all consistent with phosphorus content on the treated fabric.
Keywords: Phosphorus content; Cotton; Admicellar polymerization; Burning behavior; Thermal degradation;
Mathematical modeling of the catalytic degradation of polystyrene in the presence of aluminum chloride by Ioana A. Gianoglio Pantano; Mónica F. Díaz; Adriana Brandolin; Claudia Sarmoria (566-574).
We model the effect of the catalyst AlCl3 on polystyrene (PS). Detailed experimental studies were previously carried out on the effect of AlCl3 on PS, as part of an effort to understand how to minimize the degradation of PS during the Friedel–Crafts alkylation performed to obtain a graft copolymer from immiscible blends of PS and a polyolefin (PO). In the present work three mathematical models for the catalytic degradation of PS are proposed, all of which consider that reaction starts with the elimination of a phenyl group from the PS chain, followed by either chain scission or a change in the chain structure. The models vary in the way they consider the strength of the main chain bonds, or the reactivity of modified PS chains. Kinetic parameters for each model are estimated. Although the three proposed models could be used to represent our own experimental data, one is more accurate. Experimental data from other authors are used to evaluate its capabilities. Based on the predictions of the better model, we discuss conditions to minimize PS scission, such as operating at low temperatures and AlCl3 concentrations, and using short processing times.
Keywords: Mathematical modeling; Polystyrene degradation; Lewis acid; Molecular weight; Kinetics;
Thermal properties and degradability of poly(propylene carbonate)/poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PPC/PHBV) blends by Jian Tao; Cunjiang Song; Mingfeng Cao; Dan Hu; Li Liu; Na Liu; Shufang Wang (575-583).
Poly(propylene carbonate)/poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PPC/PHBV) blends were prepared via the solution casting method at different proportions. Their thermal characteristics were studied by means of differential scanning calorimetry (DSC) and thermogravimetry (TG). The degradability of the blends was investigated in soil suspension cultivation and in vitro degradation testing. The changes of structure and molecular weight for blends were also studied by 1H nuclear magnetic resonance spectroscopy (1H NMR), scanning electron microscopy (SEM) and gel permeation chromatography (GPC) before and after degradation. Although the PPC/PHBV blends were immiscible, the addition of PHBV could improve the thermal stability of PPC. PHBV was degraded mainly by the action of microbial enzymes in the soil suspension, which biodegraded it more rapidly than PPC in a natural environment. PPC was degraded mainly by chemical hydrolysis and random hydrolytic scission of chains in the PBS solution in vitro, and degradation of PPC was more rapid than that of PHBV in a simulated physiological environment.
Keywords: PPC/PHBV blends; Thermal properties; Biodegradability; Degradation in vitro;
Determination of scission, crosslinking and branching parameters of electron beam irradiated methacrylate–acrylamide copolymer by Khelil Slimani; Laurence Moine; Caroline Aymes-Chodur; Alexandre Laurent; Denis Labarre; Najet Yagoubi (584-590).
The aim of this work was to investigate the impact of electron beam irradiation at different dose rates on the molecular structure of linear methacrylate–acrylamide copolymer. In the first part, the radiation chemical yields of scission (G s) and crosslinking (G x ) have been determined after irradiation for various initial molecular weights CL1 (40 000 g/mol), CL2 (90 000 g/mol) and CL3 (425 000 g/mol). Based on this calculation, solvent (ethanol) was found to increase the impact of irradiation especially at low concentration of copolymer. In the second part, the presence of branching in samples before and after e-beam irradiation was explored, and branching calculation was performed.
Keywords: Irradiation; Scission; Crosslinking; Branching; Poly(methacrylate-co-acrylamide);
IR-change and yellowing of polyurethane as a result of UV irradiation by Dan Rosu; Liliana Rosu; Constantin N. Cascaval (591-596).
In this investigation IR-change and yellowing of polyurethane as a result of UV radiation were studied. In the presence of UV radiation (200 h, λ > 300 nm), the synthesized aromatic polyurethane undergoes photodegradation with gradual change of its colour. The photochemical degradation of the polyurethane is associated with the scission of the urethane group and photooxidation of the central CH2 group between the aromatic rings. These reactions are combined with the yellowing of the polyurethane surface. Analysis of the colour changes in PU surface during photodegradation was carried out by measuring CIEL∗ a ∗ b ∗ colour components (L ∗,a ∗,b ∗ and ΔEa ,b ∗). FT-IR spectroscopy was used to study the chemical changes caused by UV irradiation. The colour difference of yellowing Δ a ,b ∗ exhibits a systematic tendency to higher values with increasing irradiation time. Overall, ΔEa ,b ∗ colour change correlates well with photodegradation of polyurethane by relative increase of the concentration of carbonyl group. Our results are in agreement with the quinone (yellow colour) formation as the chromophoric reaction product of polyurethane degradation.
Keywords: Polyurethane; UV irradiation; Yellowing; Photodegradation;
Ageing and thermal degradation of plasma polymerised thin films derived from Lavandula angustifolia essential oil by C.D. Easton; M.V. Jacob (597-603).
The ageing and thermal degradation of polymer thin films derived from the essential oil of Lavandula angustifolia (LA) fabricated using plasma polymerisation were investigated. Spectroscopic ellipsometry and Fourier transform infrared (FTIR) spectroscopy were employed to monitor the optical parameters, thickness and chemical structure of the polyLA films fabricated at various RF powers over a period of 1400 h. The bulk of the degradation under ambient conditions was found to occur within the first 100 h after fabrication. The thermal degradation of the polyLA films was also investigated using the ellipsometry and FTIR. An increase in thermal stability was found for films fabricated at increased RF power levels. Between 200 and 300 °C, the properties indicate that a phase change occurs in the material. Samples annealed up to 405 °C demonstrated minimal residue, with retention ranging between 0.47 and 2.2%. A tuneable degradation onset temperature and minimal residue post-anneal demonstrate that the polyLA films are excellent candidates for sacrificial material in air gap fabrication.
Keywords: Plasma polymer; Ellipsometry; FTIR; Oxidation; Sacrificial material;
Chemical recycling of PET waste into hydrophobic textile dyestuffs by S.R. Shukla; Ajay M. Harad; Laxmikant S. Jawale (604-609).
The paper aims at effective chemical recycling of poly(ethylene terephthalate) (PET) fiber waste into useful products, such as hydrophobic disperse dyes for synthetic textiles. For this, PET fiber waste was glycolytically depolymerized using excess of ethylene glycol in the presence of sodium sulfate as catalyst. The product, pure bis(2-hydroxyethylene terephthalate) (BHET) was obtained with >60% yield by successive recrystallization. In order to synthesize hydrophobic disperse dyes, applicable to synthetic textile fibers, BHET was converted to bis(2-chloroethylene terephthalate), reacted with the p-nitro benzoic acid, reduced and then reacted with bromine and potassium thiocyanate to get benzothiazole derivative. Coupling with N,N-diethylaniline produced a bright yellow disperse dye (Dye A). Similarly, coupling of p-amino benzoic ester with N,N-diethylaniline led to an orange colored disperse dye (Dye B). These dyes were applied onto polyester fabric by conventional method. Results in terms of depth of dyeing, evenness and the performance characteristics were found to be promising.
Keywords: PET fiber waste; Glycolysis; BHET; Benzothiazole; Disperse dye;
Diglycidylphenylphosphate based fire retardant liquid crystalline thermosets by P. Sudhakara; P. Kannan (610-616).
Organophosphorus liquid crystalline thermosets (LCTs) were developed using diglycidylphenylphosphate (DGPP) and various aromatic diamines. DGPP was prepared by the esterification of phenylphosphorodichloridate with glycidol. 2,5-Bis(p-aminophenyl)-1,3,4-oxadiazole (BPOD) was synthesized and three different commercial diamines, 4,4′-diaminodiphenyl sulphone (DDS), 4,4′-diaminodiphenyl methane (DDM) and biphenyl diamine (BPD) were used as curing agents. The mesomorphic behaviour of DGPP/diamine mixtures and their curing kinetics were monitored by differential scanning calorimetry and hot stage optical polarized microscopy. The thermogravimetric analysis data showed that the LCTs are stable in the range 261–292 °C and afford 36–48% char yield. The limiting oxygen index values are between 35 and 47 proving fire retardance. The mechanical properties of the cured LCTs were characterized by dynamic mechanical analysis.
Keywords: Organophosphorus resin; Mesophase; Liquid crystalline thermosets; HOPM; Char yield; LOI;
Synthesis, characterization, thermal properties and flame retardancy of a novel nonflammable phosphazene-based epoxy resin by Ran Liu; Xiaodong Wang (617-624).
Hexakis(4-hydroxyphenoxy)-cyclotriphosphazene (PN–OH) was synthesized through nucleophilic substitution of the chloride atoms of hexachlorocyclotriphosphazene and reduction of the aldehyde groups, and its chemical structure was characterized by elemental analysis, 1H and 31P NMR, and Fourier transform infrared (FTIR) spectroscopy. A new phosphazene-based epoxy resin (PN-EP) was successfully synthesized through the reaction between diglycidyl ether of bisphenol-A (DGEBA) and PN–OH, and its chemical structure was confirmed by FTIR and gel permeation chromatography. Four PN-EP thermosets were obtained by curing with 4,4′-diaminodiphenylmethane (DDM), dicyandiamide (DICY), novolak and pyromellitic dianhydride (PMDA). The reactivity of PN-EP with the four curing agents presents an increase in the order of DDM, PMDA, novolak and DICY. An investigation on their thermal properties shows that the PN-EP thermosets achieve higher glass-transition and decomposition temperatures in comparison with the corresponding DGEBA ones while their char yields increase significantly. The PN-EP thermosets also exhibit excellent flame retardancy. The thermosets with novolak, DICY and PMDA achieve the LOI values above 30 and flammability rating of UL94 V-0, whereas the one with DDM reaches the V-1 rating. The nonflammable halogen-free epoxy resin synthesized in this study has potential applications in electric and electronic fields in consideration of the environment and human health.
Keywords: Flame retardancy; Phosphazene; Epoxy resin; Synthesis; Thermal stability;
Metal compound-enhanced flame retardancy of intumescent epoxy resins containing ammonium polyphosphate by Jun-Sheng Wang; Yun Liu; Hai-Bo Zhao; Jiang Liu; De-Yi Wang; Yan-Peng Song; Yu-Zhong Wang (625-631).
A series of intumescent flame-retardant epoxy resins (IFR-EPs) were prepared only by adding a 5 wt% total loading of ammonium polyphosphate (APP) and metal compounds. All the samples could achieve V-0 rating and did not generate dripping during UL-94 testing. The limiting oxygen index (LOI) values of the samples with 4.83 wt% APP and 0.17 wt% CoSA increase from 27.1 to 29.4, compared with epoxy resin containing 5 wt% APP. The samples also showed excellent water resistance of flame retardancy in 30 °C and 70 °C water for 168 h. The LOI results show that the composition of metal compounds (metal ions and ligands/anions) and the mass ratios of APP to metal compounds affect the flame retardancy of the samples. TG results indicate that the catalytic effect of CoSA on the decomposition of both APP and the epoxy resins containing APP is better than that of CuSAO. The fire behavior of epoxy resin and epoxy resins containing APP with/without CoSA were investigated by cone calorimeter. Cone calorimeter parameters of the samples such as HRR, THR, TSP and COP indicate that the addition of APP and CoSA improves the fire safety of epoxy resin significantly, and CoSA shows an obvious catalytic effect.
Keywords: Ammonium polyphosphate; Epoxy resin; Intumescence; Flame retardance; Catalysis;
Crystallization behavior and thermal property of biodegradable poly(butylene succinate)/functional multi-walled carbon nanotubes nanocomposite by Liang Song; Zhaobin Qiu (632-637).
Biodegradable poly(butylene succinate) (PBSU)/functional multi-walled carbon nanotubes (f-MWNTs) nanocomposite were prepared by melt compounding. Nonisothermal crystallization and subsequent melting behavior, isothermal crystallization kinetics, spherulitic morphology, and crystal structure of neat PBSU and its nanocomposite were studied by differential scanning calorimetry, optical microscopy and wide angle X-ray diffraction in detail. The presence of f-MWNTs has a significant heterogeneous nucleation effect on the crystallization and morphology of PBSU, resulting in that the crystallization is enhanced during both nonisothermal and isothermal crystallization in the nanocomposite. Moreover, the crystal structure of PBSU is not modified by f-MWNTs in the nanocomposite. The thermogravimetric analysis illustrates an improvement in thermal stability of PBSU by around 10 °C in the presence of f-MWNTs compared with that of neat PBSU.
Keywords: Poly(butylenes succinate); Multi-walled carbon nanotube; Crystallization kinetics; Thermal property;
Mechanisms for surface energy changes observed in plasma immersion ion implanted polyethylene: The roles of free radicals and oxygen-containing groups by Alexey Kondyurin; Pourandokht Naseri; Keith Fisher; David R. McKenzie; Marcela M.M. Bilek (638-646).
Low density polyethylene (LDPE) was modified by plasma immersion ion implantation (PIII) with nitrogen ions of 20 keV. Surface energy and structural transformations were observed during storage of the modified LDPE in air after PIII, by wettability measurements and FTIR–ATR spectra respectively. The appearance of oxygen-containing groups has some kinetic stages with characteristic times from hours to days. The surface energy values attained and comparison with the kinetics of oxidation reveal that the initial changes in the surface energy of LDPE are caused mainly by free radicals and to a lesser extent by oxygen-containing groups. The final surface energies observed after the process known as hydrophobic recovery and the surface energies stabilize are attributable to oxygen-containing groups. The modified surface is “living” and an investigation of the wettability, surface energy, unsaturated and oxygen-containing groups in the surface layer of ion beam modified polymers is incomplete if the kinetics of structural transformations after modification is not taken into account.
Keywords: Plasma immersion ion implantation; Polyethylene; FTIR; Wettability; Surface energy; Kinetics;
Stabilization of polyurethanes based on liquid OH-telechelic polybutadienes: Comparison of commercial and polymer-bound antioxidants by Jiří Podešva; Jana Kovářová; Miluše Hrdličková; Miloš Netopilík (647-650).
A soluble polyurethane was synthesized by a reaction of OH-telechelic, 1,2-rich, low-molecular-weight polybutadiene with toluene 2,4-diisocyanate. To the pendent vinyls of the polybutadiene blocks of the polyurethane, a sterically hindered phenolic antioxidant bearing a sulfanyl group (i.e., 6-sulfanylhexyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate) was added by a free-radical mechanism (in varying degrees of conversion). The self-stabilized polyurethane thus formed, bearing the antioxidant structures as side chains, was mixed in varying concentrations with the original (unstabilised) polyurethane and the thermo-oxidative stability of the mixtures was evaluated by DSC in air. The antioxidant effect of the polymeric stabilizer on the oxidative stability of polyurethane, expressed as the oxidation onset temperature, is approximately the same as that of a low-molecular-weight analogue, the commercial octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate (Irganox 1076), as related to the same molar concentration of the phenolic moiety, but the former is superior to the latter due to its ability to persist in the matrix. In both cases, the onset temperature of oxidation increases with increasing mole ratio of the phenolic structure and the total butadiene units in the mixture.
Keywords: Polyurethanes; Liquid polybutadienes; Polymeric antioxidants; Thermo-oxidation; DSC;
Surface molecular characterisation of different epoxy resin composites subjected to UV accelerated degradation using XPS and ToF-SIMS by Firas Awaja; Paul J. Pigram (651-658).
Epoxy resin composites reinforced with E-glass (E), 3D glass (3D) and carbon fibre (CF) were subjected to an intense UV and high temperature accelerated degradation environment. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to provide a molecular characterisation of the surface of the degraded composites. The response at the surface of the epoxy resin composites to oxidative degradation is influenced by the composite reinforcement type and characteristics. XPS results indicate that 3D resin composites exhibit more surface oxidation as a result of the accelerated degradation in comparison with E and CF composites. Principal components analysis (PCA) of the ToF-SIMS positive ion spectra showed that E and 3D resin composites suffered chain scission while CF composites suffered chain scission and cross-linking reactions as a result of the intense UV exposure. The extent of the surface oxidation, cross-linking/condensation reaction and loss of low molecular weight (lower than C4H x ) aliphatic hydrocarbons may be indicated using PCA of both the ToF-SIMS positive and negative ion spectra. PCA also provides insight for proposing epoxy resin chain scission and oxidation reaction mechanisms.
Keywords: ToF-SIMS; XPS; Accelerated degradation; Epoxy resin; UV;
Oxo-biodegradable polyolefins show continued and increased thermal oxidative degradation after exposure to light by Nils B. Vogt; Emil Arne Kleppe (659-663).
Samples of polyethylene (PE) and polypropylene (PP) with 2% Renatura™ pro-oxidant additive were subjected to varying times of weathering (UVCON; ISO 4892-3), transferred to dark thermal exposure (at 70 °C) and the subsequent degradation monitored by measuring elongation at break and tensile strength during intervals up to 45 days. The results demonstrate that the oxidative degradation, after initial light exposure, continues more rapidly in the dark thermal conditions and that increased exposure to light increases thermal oxidative degradation.
Keywords: Oxo-biodegradation; Photo-oxo-degradation; Thermal degradation; Iron-based oxo-biodegradable additive; Landfill; Composting;
An analysis of the thermal aging behaviour in high-performance energetic composites through the glass transition temperature by José Luis de la Fuente (664-669).
Differential scanning calorimetry (DSC) was used to analyze the thermal aging behaviour in energetic composite materials where a hydroxyl-terminated polybutadiene (HTPB)/isophorone diisocyanate elastomer is the polymeric matrix. Different parameters from the analysis of the glass transition, such as the glass transition temperature (T g), were used in order to monitor this isothermal aging at 65 °C during a total time of 3000 h, finding an increasing and broadening T g. In addition, the accelerated aging behaviour of these materials was also studied by a classical method, based on the change of mechanical properties such as those of Young's modulus or strain at break. The correlation between both methodologies was examined, demonstrating that an analytical technique such as DSC allows the evaluation of the actual state of composite solid propellants with a small sample and a straightforward measurement.
Keywords: Composite solid propellant; Thermal aging; DSC; Glass transition temperature; Mechanical properties;
Effect of ZnO and organo-modified montmorillonite on thermal degradation of poly(methyl methacrylate) nanocomposites by A. Laachachi; D. Ruch; F. Addiego; M. Ferriol; M. Cochez; J.-M. Lopez Cuesta (670-678).
Since a few years ago, a topic of interest consists in developing composites filled with nanofillers to improve thermal degradation and flammability property of poly(methyl methacrylate) (PMMA). In the present work, the effects of ZnO nanoparticles and organo-modified montmorillonite (OMMT) on the thermal degradation of PMMA were investigated by thermogravimetric analysis (TGA). PMMA–ZnO and PMMA–OMMT nanocomposites were prepared by melt blending with different (2, 5, and 10 wt%) loadings. SEM and TEM analyses of nanocomposites were performed in order to investigate the dispersion of nanofillers in the matrix. According to TGA results, the addition of ZnO nanoparticles does not affect the thermal degradation of PMMA under an inert atmosphere. However, in an oxidative atmosphere, two contrary effects were observed, a catalytic effect at lower concentration of ZnO in the PMMA matrix and a stabilizing effect when the ZnO concentration is higher (10 wt%). In contrast, the presence of OMMT stabilizes the thermal degradation of PMMA whatever be the atmosphere. Differential thermal analysis (DTA) curves showed surprising results, because a dramatic change of exothermic reaction of the PMMA degradation process to an endothermic reaction was observed only in the case of OMMT. During the degradation of PMMA–ZnO nanocomposites, pyrolysis-gas chromatography coupled to mass spectrometer (Py-GC/MS) showed an increase in the formation of methanol and methacrylic acid while a decrease in the formation of propanoic acid methyl ester occurred. In the case of PMMA–OMMT systems, a very significant reduction in the quantity of all these degradation products of PMMA was observed with increasing OMMT concentration. It is also noted that during PMMA–OMMT degradation less energy was released as the decomposition is an endothermic reaction and the material was cooled.
Keywords: Thermal degradation; Poly(methyl methacrylate); PMMA; Nanocomposite; ZnO; Nanoparticles;
Thermal stability of ion-exchange Nafion N117CS membranes by Yasunori Iwai; Toshihiko Yamanishi (679-687).
The effect of exchanged ions on the thermal stability of Nafion N117CS membranes was investigated by X-ray photoelectron spectra (XPS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and ion exchange capacity determinations. The ion exchange of alkaline metal ions was effective in improving the thermal stability of the Nafion N117CS membrane. Findings reveal that when Nafion was exchanged for cations with a larger ionic radius, the membrane attained superior thermal stability. On the other hand, we confirmed that the Na-exchange Nafion N117CS membrane possessed a distinctive degree of thermal stability among the alkaline ion-exchange Nafions, although the order of ionic radii is K > Na > Li. Thermal stability improved the most when the Nafion membrane was exchanged for alkaline ions, followed by divalent ions, then trivalent ions. As for the Nafion membrane when it was exchanged for divalent ions or trivalent ions, Nafion following the ion exchange had a thermal stability proportional to an increase in the ionic radius of the cation. This stability may be explained by the reduction of water content and a greater interaction between the sulfonate groups and the cations with larger ionic radii. Since the Al cations acted as a Lewis acid center, the decomposition of the ether bonds of the perfluoroalkylether pendant-chains of the Nafion membrane was observed for the Nafion N117CS membrane that had been exchanged for Al ions. The activation of molecular mobility in Nafion was observed between the decomposition stages of the loss of water and the loss of sulfonic groups. The temperature of activation of cation-exchange Nafion became much higher than that of Nafion in an acid form.
Keywords: Nafion; Thermal stability; Ionic radii; X-ray photoelectron spectra; Thermogravimetric analysis; Differential scanning calorimetry;
Lipase-catalysed degradation of copolymers prepared from ɛ-caprolactone and dl-lactide by Sebastien Lenglet; Suming Li; Michel Vert (688-692).
A series of copolymers were prepared by ring-opening polymerization of ɛ-caprolactone and dl-lactide, using zinc lactate as catalyst. The resulting PCL/PLA copolymers were characterized by various analytical techniques such as NMR, SEC, DSC and X-ray diffraction. The [CL]/[LA] ratios of the copolymers are very close to those in the feed, indicating a good conversion of monomers. The copolymers with CL contents higher than 50% appear semi-crystalline, the crystalline structure being of the PCL-type. Compression moulded polymer films were allowed to degrade in a pH = 7.6 phosphate buffer containing Pseudomonas lipase. Data show that copolymers with CL contents lower than 25% are not degradable and the degradation rate increases with CL content for CL-rich copolymers. Various soluble degradation products are detected in the degradation medium, including CL1 to CL3 and LA1 to LA4 homo-oligomers, and CL2LA1 co-oligomer. The presence of LA homo-oligomers and CL2LA1 co-oligomer suggests that Pseudomonas lipase can not only degrade PCL but also LA short blocks along PCL/PLA copolymer chains. On the other hand, little changes of composition are detected during degradation, in agreement with a surface erosion mechanism as shown by ESEM.
Keywords: Biodegradation; Enzymatic degradation; Poly(ɛ-caprolactone); Poly(dl-lactide); Copolymer; Lipase;
Void formation due to gas evolution during the recycling of Acrylonitrile–Butadiene–Styrene copolymer (ABS) from waste electrical and electronic equipment (WEEE) by J.C. Arnold; S. Alston; A. Holder (693-700).
During processing of recycled ABS and ABS/HIPS blends, voiding defects can occur within the resulting material which can result in deterioration of mechanical properties. The voids were previously thought to be caused by the evolution of volatile substances during processing. This study investigated the recycling of post-consumer ABS from a variety of types of WEEE. The mechanical properties of the processed material were assessed and a combination of visual observation during processing and optical microscopy was used to identify the extent of voiding. It was found that flexural strength and ductility in particular decreased with increased levels of voids. The gases emitted during heating and processing were analysed using Gas Chromatography with Mass Spectroscopy (GCMS) and were found to be breakdown products of the original polymers. These seem to be present in the WEEE, either as polymerization residuals or as products of degradation during the initial service life rather than degradation products from reprocessing. The amounts of volatiles liberated were quantified, which showed that the volatile emissions from post-consumer material were of a similar magnitude to those seen with virgin material. More intensive or longer processing led to a reduction in the emissions and voiding and an improvement in strength, suggesting that there is a finite potential for volatile liberation, and that the problem could be overcome by the use of suitable processing conditions.
Keywords: Recycling; ABS; Volatile emissions; Mechanical properties; GCMS;
Influence of cubic α-Fe2O3 particles on the thermal stability of poly(methyl methacrylate) synthesized by in situ bulk polymerization by E. Džunuzović; M. Marinović-Cincović; K. Jeremić; J. Nedeljković (701-704).
Poly(methyl methacrylate)/α-Fe2O3 composites were prepared by in situ bulk radical polymerization of methyl methacrylate in the presence of the cubic α-Fe2O3 particles using 2,2′-azobisisobutyronitrile as initiator. The cubic α-Fe2O3 particles were synthesized by forced hydrolysis of FeCl3 and characterized by X-ray diffraction analysis and transmission electron microscopy. The molar masses and molar mass distribution of synthesized PMMA samples were determined by gel permeation chromatography. The influence of α-Fe2O3 filler particles on the thermal properties of the PMMA matrix was investigated using thermogravimetry and differential scanning calorimetry. The molar mass and polydispersity of PMMA extracted from composite samples were not influenced by cubic α-Fe2O3 particles. The obtained composites have better thermal and thermooxidative stability than pure PMMA. On the other hand, the values of the glass transition temperature of composite samples were identical to the glass transition temperature of pure PMMA.
Keywords: PMMA; α-Fe2O3; Composite; Bulk radical polymerization; Thermal stability;
The role of the trivalent metal in an LDH: Synthesis, characterization and fire properties of thermally stable PMMA/LDH systems by Charles Manzi-Nshuti; Dongyan Wang; Jeanne M. Hossenlopp; Charles A. Wilkie (705-711).
Two layered double hydroxides (LDHs), calcium aluminum undecenoate (Ca3Al) and calcium iron undecenoate (Ca3Fe), have been prepared by the co-precipitation method. XRD analysis of these LDHs reveals that they are layered materials and FT-IR and TGA confirmed the presence of the undecenoate anions in the material produced. The PMMA composites were prepared by bulk polymerization and the samples were characterized by XRD, TEM, TGA and cone calorimetry. Both additives greatly enhance the thermal stability of PMMA, while the calcium aluminum LDH gives better results when the fire properties were examined using the cone calorimeter.
Keywords: Layered double hydroxides; Nanocomposites; Poly(methyl methacrylate); Fire retardancy;
The role of organoclay and matrix type in photo-oxidation of polyolefin/clay nanocomposite films by L. Botta; N.Tz. Dintcheva; F.P. La Mantia (712-718).
In this paper the photo-oxidation behaviour of polyolefin/clay nanocomposite films was studied; in particular, the effect of the amount of organo-modifier and the matrix polarity on the photo-oxidation was investigated. Two different organo-modified clays and compositions of LDPE/EVA blend films were used and the photo-oxidation was followed by mechanical and spectroscopic analyses.The organoclay and matrix type strongly influence the photo-oxidative behaviour of nanocomposite films. The films filled with CL15A show a faster loss of mechanical performance and higher carbonyl formation with respect to the films filled with the CL20A. Additionally, the LDPE based nanocomposite undergoes photo-oxidation more rapidly than the EVA based one.
Keywords: Photo-oxidation; Carbonyl index; Organo-modified clay; Polyethylene; Poly(ethylene-co-vinyl acetate);
Melt stabilisation of Phillips type polyethylene, Part I: The role of phenolic and phosphorous antioxidants by Ildikó Kriston; Ágnes Orbán-Mester; Gábor Nagy; Peter Staniek; Enikő Földes; Béla Pukánszky (719-729).
The role of a phenolic and three phosphorous (phosphite, phosphonite and phosphine) antioxidants in the melt stabilisation of polyethylene was studied in a Phillips type polyethylene by multiple extrusions. The polyethylene was stabilised with a single antioxidant at 700 ppm and with phenolic/phosphorous antioxidant combinations containing 700 ppm of each component. The functional groups (methyl, vinyl, vinylidene, trans-vinylene and carbonyl) of polyethylene and the residual amount of phosphorous antioxidants were analysed quantitatively by FT-IR methods developed in our laboratory. The rheological characteristics, the colour and the residual thermo-oxidative stability of the polymer were determined and compared. Blown films were prepared and their mechanical strength measured by the Elmendorf and Dart-drop tests. The comparison of the different characteristics revealed that the chemical reactions taking place during the first processing of the nascent polymer powder, as well as the chemical composition of the antioxidants determine the reactions taking place in further processing operations. The changes in the characteristics of stabilised polyethylene during processing are controlled by the phosphorous stabiliser. The effect and final result depend on the chemical structure of the given antioxidant. The phenolic antioxidant itself does not hinder the formation of long chain branches. It reduces the rate of oxidation of the various phosphorous stabilisers, but does not modify the mechanism of stabilisation of the phosphonite and the phosphine. The reactions of the phosphite are significantly modified by the presence of a phenolic antioxidant.
Keywords: Polyethylene; Phenolic antioxidant; Phosphorous antioxidant; Stabilisation;
Synthesis and characterization of biodegradable pH-sensitive hydrogels based on poly(ɛ-caprolactone), methacrylic acid, and poly(ethylene glycol) by Ke Wang; Shao Zhi Fu; Ying Chun Gu; Xu Xu; Peng Wei Dong; Gang Guo; Xia Zhao; Yu Quan Wei; Zhi Yong Qian (730-737).
In this work, a novel biodegradable pH-sensitive hydrogel based on poly(ɛ-caprolactone) (PCL), methoxpoly(ethylene glycol) (MPEG) and methacrylic acid (MAA) was prepared by UV-initiated free radical polymerization. The resulting macromonomers and hydrogels were characterized by FTIR and/or 1H NMR. Swelling behaviour and pH sensitivity of the hydrogels were studied in detail. With increase in pH of aqueous medium from 1.2 to 7.2, swelling ratio of the hydrogels increased accordingly. The hydrolytic degradation behaviour was also investigated. The prepared biodegradable pH-sensitive hydrogel based on PCL, MPEG, and MAA might have great potential application in smart drug delivery system.
Keywords: Biodegradable; pH sensitive; Degradation; Water absorption; Dynamic swelling/deswelling;
Thermal degradation of poly(vinylpyridine)s by Ayşegül Elmaci; Jale Hacaloglu (738-743).
The thermal stability and the temperature at which maximum degradation yields are detected were quite similar for both poly(2-vinylpyridine) (P2VP) and poly(4-vinylpyridine) (P4VP). However, considerable differences among the thermal degradation products of both polymers were detected indicating a correlation between the polymer structure and the degradation mechanism. Direct pyrolysis mass spectrometry analyses revealed that P2VP degrades via a complex degradation mechanism, yielding mainly pyridine, monomer, and protonated oligomers, whereas depolymerization of P4VP takes place in accordance with the general thermal behaviour of vinyl polymers. The complex thermal degradation behaviour for P2VP is associated with the position of the nitrogen atom in the pyridine ring, with σ-effect.
Keywords: Poly(vinylpyridine); Thermal degradation; Pyrolysis; Mass spectrometry;
Synthesis and UV absorption properties of 2,3-dihydroxynaphthalene-6-sulfonate anion-intercalated Zn–Al layered double hydroxides by Hao Chai; Xiangyu Xu; Yanjun Lin; David G. Evans; Dianqing Li (744-749).
An organic UV absorbent has been intercalated into a layered double hydroxide (LDH) host by ion exchange of a Zn–Al–LDH-nitrate precursor with a solution of 2,3-dihydroxynaphthalene-6-sulfonic acid (DNSA) sodium salt in water. After intercalation of the UV absorbent, the powder X-ray diffraction (XRD) pattern shows that the interlayer distance in the LDHs increases from 0.90 to 1.59 nm. The possible structure is that the interlayer DNSA anions arrange in a monolayer and in a perpendicular orientation toward the hydroxide layers. Infrared spectra and TG–DTA curves reveal the presence of a complex system of supramolecular host–guest interactions between layers. The thermal stability of the intercalated UV absorbent was investigated by TG–DTA and it was found that this material is more stable than the original organic UV absorbent at high temperature, showing that the thermostability is markedly enhanced after intercalation into the LDH host. The UV absorbent-intercalated LDHs exhibit excellent UV photostability in polypropylene composites.
Keywords: Absorption; Composites; Crystallization; Layered double hydroxides; Intercalation; Stability;