Polymer Degradation and Stability (v.99, #C)
Editorial Board (IFC).
High char yield of aryl boron-containing phenolic resins: The effect of phenylboronic acid on the thermal stability and carbonization of phenolic resins by Shujuan Wang; Xinli Jing; Yong Wang; Jingjing Si (1-11).
This work reports an aryl boron-containing phenolic resin (PR) exhibiting an extremely high thermal decomposition temperature and char yield and formed by reacting phenylboronic acid (PBA) with PR. DSC was used to study the curing behaviour of the PBA modified PR (PBPR). The structure and thermal properties of the cured PBPR were investigated by FTIR, XPS, 11B NMR and TGA. Phenylboronates were formed during the curing of PBPR, which reduced the distance between benzene rings. The TGA indicates that the temperature with the maximum decomposition rate increased for the cured PBPR by 56 °C, and the charring yield increased by 13.4 per cent (800 °C, nitrogen atmosphere) relative to PR. FTIR, XPS, XRD, 11B NMR and Raman analyses were used to study the structural evolution of the cured PBPR during pyrolysis. Boron oxide was formed during the char formation from the cleavage of B–C and B–O–C bonds via pyrolysis, which effectively avoided the release of volatile carbon oxides and retained the carbon. In addition, incorporating boron into the carbon lattice increases the crystallite height and decreases the interlayer spacing. These findings reveal that PBA exhibited obvious effects in improving the thermal stability and promoting the graphite crystallites of PR during carbonization.
Keywords: Aryl boron-containing phenolic resin; Thermal properties; High char yield; Carbonization; Phenylboronic acid;
Flame retardant effect of boron compounds on red phosphorus containing epoxy resins by Mehmet Dogan; S. Murat Unlu (12-17).
The effect of zinc borate (ZnB), boric acid (BA) and boric oxide (B2O3) was studied on the flame retardant and thermal stability properties of epoxy resin containing red phosphorus (RP). The flame retardancy of epoxy based composites was investigated using limiting oxygen index (LOI), UL-94 standard, thermogravimetric analysis (TGA), mass loss calorimeter, scanning electron microscopy (SEM) and attenuated total reflectance – fourier-transform infrared spectroscopy (ATR-FTIR). The addition of 15 wt% RP based flame retardant additive increased the LOI value from 19.5 to 32.5 and V0 rating was obtained from UL-94 test. According to flammability properties, the maximum adjuvant effect was observed at ratio of 9:1 (RP:boron compounds) with the addition of ZnB and BA and at a ratio of 7:3 with the addition of B2O3. With the partial substitution of boron compounds for RP, lower heat release rate (HRR) and total heat evolved (THE) was obtained. According to fire performances, ZnB containing composite showed lowest HRR and THE values. The boron compounds showed beneficial effect by increasing char yield in the condensed phase.
Keywords: Red phosphorus; Zinc borate; Boric acid; Boric oxide; Flame retardant;
Synergistic effect of activated carbon and Ni2O3 in promoting the thermal stability and flame retardancy of polypropylene by Jiang Gong; Nana Tian; Jie Liu; Kun Yao; Zhiwei Jiang; Xuecheng Chen; Xin Wen; Ewa Mijowska; Tao Tang (18-26).
A novel combined catalyst of activated carbon (AC) with Ni2O3 was demonstrated to be much more efficient than AC or Ni2O3 alone in enhancing the char yield of polypropylene (PP) and improving its char layer structure, which greatly improved the thermal stability and flame retardancy of PP. The results of X-ray diffraction, field-emission scanning electron microscope and transmission electron microscope revealed that the residual char mainly consisted of carbon nanotubes (CNTs). Thermal gravimetric analyses results indicated that the combination of AC and Ni2O3 dramatically enhanced the thermal stability of PP. The flame retardancy of PP and its composites was studied by cone calorimeter test. The heat release rate and total heat release of the ternary PP/7.5AC–7.5Ni2O3 composite decreased significantly in comparison with those of neat PP. The investigation of the synergetic mechanism showed that in the presence of both AC and Ni2O3, a large amount of CNTs were in situ formed from the degradation products of PP during combustion. This not only reduced the release of flammable degradation products of PP, but also acted as a thermal shield for energy feedback from the flame. In addition, the formation of a network-like structure of AC and Ni2O3 particles in PP matrix favored the formation of a more compacted protective layer, which enhanced the flame retardancy of PP.
Keywords: Polypropylene; Activated carbon; Ni2O3; Flame retardancy; Thermal stability;
Synthesis of maleimido-substituted aromatic s-triazine and its application in flame-retarded epoxy resins by Yongzhen Wang; Jianqing Zhao; Yanchao Yuan; Shumei Liu; Zhengming Feng; Ying Zhao (27-34).
In this study, a maleimido-substituted aromatic s-triazine (TMT) was synthesized successfully via the nucleophilic substitution reaction between cyanuric chloride and N-(4-hydroxyphenyl) maleimide (HPM) formed from paraaminophenol and maleic anhydride; and its structure was characterized by flourier transform infrared spectroscope (FT-IR), 1H and 13C nuclear magnetic resonance (NMR), and elemental analysis (EA). The studied flame-retarded epoxy resins were obtained via thermal curing reactions among 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) modified epoxy prepolymer (DOPOER), 4,4′-diaminodiphenyl ethane (DDM) and TMT. Cure kinetics, flame-retardant, thermal and mechanical properties of the cured epoxy resins were characterized by differential scanning calorimeter (DSC), thermogravimeric analysis (TGA), limited oxygen index (LOI) measurement, UL 94 vertical burning test and mechanical test. The results indicate that TMT can promote the curing reaction of epoxy resins and decrease its apparent activation energy (E a). Introduction of TMT can greatly improve flame-retardant, thermal and mechanical properties of the cured epoxy resins. Compared with the DOPOER/DDM system without TMT, LOI value of the cured epoxy resin can increase from 36.4% to 51.8%, and all samples can pass UL 94 V-0 rate when TMT content ranges from 1.98 wt% to 7.44 wt%. Its initial degradation temperature and glass transition temperature (T g) can increase maximally by 37.6 °C and 12.6 °C, respectively when TMT content is 3.88 wt%.
Keywords: Epoxy resins; Triazine; Flame-retarded; Thermal properties;
Flame retardance and thermal degradation mechanism of polystyrene modified with aluminum hypophosphite by Yuan-Wei Yan; Jian-Qian Huang; Ya-Hui Guan; Ke Shang; Rong-Kun Jian; Yu-Zhong Wang (35-42).
A phosphorus-containing inorganic compound, aluminum hypophosphite (AP), was used to prepare flame-retardant polystyrene (PS). The flammability of the PS/AP composites was investigated by the limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter test. When the content of AP reaches 25 wt%, the LOI of PS/AP is 25.6% and it passes UL-94 V-0 rating. The results of cone calorimeter test show that the heat release rate (HRR), the total heat release (THR) and the mass loss rate (MLR) of PS/AP composites are significantly reduced. The thermal degradation mechanism of PS/AP was investigated by thermogravimetric analysis (TGA), Fourier transform infrared spectrometry (FTIR), thermal gravimetric-Fourier transform infrared spectrometry (TG-FTIR), pyrolysis gas chromatography-mass spectrometry (Py-GC/MS), and X-ray photoelectron analysis (XPS) tests. The results indicate that PS/AP has a combined gas-phase and condensed-phase activity in the combustion and degradation of the composites. Consequently, a possible flame-retardant mechanism of PS/AP composites is proposed.
Keywords: Polystyrene; Aluminum hypophosphite; Flame-retardant mechanism; Gas-phase activity; Cone calorimetry;
Synthesis of a novel dicyclic silicon-/phosphorus hybrid and its performance on flame retardancy of epoxy resin by Shiqiang Song; Jiajun Ma; Ke Cao; Guanjun Chang; Yawen Huang; Junxiao Yang (43-52).
A novel silicon-/phosphorus hybrid (SDPS) was synthesized by a condensation polymerization of diphenylhydroxysilane and spirocyclic pentaerythritol di(phosphate monochloride). The use of SDPS and the cooperative use of SDPS with P–N hybrid in flame retardant epoxy resin (EP) were investigated. Limiting oxygen index and cone calorimeter tests showed that the loading of SDPS and the cooperative use of SDPS and P–N hybrid in EP provided enhanced fire resistance. TGA, TG-FTIR and SEM measurements revealed that the enhancement in fire resistance was arising from the formation of a compact honeycomb carbonaceous structure hybridized by silica, the good char forming ability and the inhibition of flammable gas release. Further analysis from Raman spectra revealed that the compact carbonaceous layer may be originated from an increase in ordering of amorphous carbonaceous layer.
Keywords: Epoxy resin; Flame retardancy; Silicon-/phosphorus hybrid; Condensation polymerization;
Synthesis and properties of flame-retardant poly(vinyl alcohol)/pseudo-boehmite nanocomposites with high transparency and enhanced refractive index by Yuhang Cai; Mengmeng Zhao; Henti Wang; Yongjin Li; Zhigang Zhao (53-60).
Flame-retardant nanocomposites with high transparency based on poly (vinyl alcohol) (PVA) and pseudo-boehmite nanorods have been fabricated by synthesis of pseudo-boehmite nanorods and subsequent solution blending with PVA. The morphology and physical properties of PVA/pseudo-boehmite nanocomposites have been characterized systematically. Scanning electron microscopy investigations showed the homogeneous dispersion of pseudo-boehmite nanorods within PVA matrix even at very high nanorods loadings. The nanocomposites with 37.5 wt% pseudo-boehmite nanorods exhibit limit oxygen index (LOI) as high as 30.0 with the transmittance of more than 90% at the visible region and the enhanced refractive index. Moreover, the incorporation of the pseudo-boehmite nanorods increases the modulus and the tensile strength of PVA, indicating the significantly enhanced surface hardness of the nanocomposite. It is considered that the prepared PVA nanocomposites are not only useful as flame-retardant fibers, a long term pursued target for PVA fabrics, but also as optical appliances with its excellent transparency and high refractive index.Display Omitted
Keywords: Pseudo-boehmite nanorods; Nanocomposites; Transparency; Flame retardancy;
Thermomechanical degradation of polyethylene/polyamide 6 blend-clay nanocomposites by M.C. Mistretta; M. Morreale; F.P. La Mantia (61-67).
Polymer nanocomposites are gaining a growing interest both in the academia and in the industrial field, because of some specific properties they can assure. However, the rise in the attention from the industry is also leading to concerns about their processing, which can involve issues which are not present in traditional polymers processing; furthermore, additional issues can arise when nanocomposites are based on a polymer blend rather than a single polymer. In this work, a systematic study on thermomechanical degradation and reprocessing behaviour of LDPE/PA6/Cloisite 15A systems has been performed. The characterization was based on rheological, mechanical and morphological analysis. The investigation revealed a complex degradation behaviour, including the degradation phenomena involving the filler and those involving the two components of the polymer blend; furthermore, these phenomena are strongly dependent on the specific processing conditions.
Keywords: Polymer blends; Nanocomposites; Thermomechanical degradation; Processing;
Spectral analysis of changes to pine and oak wood natural polymers after short-term waterlogging by Anna Sandak; Jakub Sandak; Leszek Babiński; Dusan Pauliny; Mariapaola Riggio (68-79).
Non-destructive spectroscopic methods (UV–Vis, FT–NIR and XRF) were utilized to evaluate the degradation state of natural polymers of contemporary wood exposed to short-term (eight years) waterlogging. Experimental samples included both softwood (Scots pine) and hardwood (Penduculate oak) degraded in two differing environments (peat and water). The species investigated exhibited diverse mechanisms of degradation. Differing sites also seem to have influenced degradation kinetics. Samples of both species placed in trenches filled with water show slightly more intense degradation. However, interpretation of FT–NIR spectra revealed that different woody polymers (functional groups) were degraded in waterlogged pine and oak respectively. Characteristic darker color was observed in oak wood with progressive waterlogging. XRF analysis identified deposition of iron in the external zone of oak samples. Partial Least Square prediction models for exposure time of wood decomposed in wet environment were also developed. The degradation stage of the short-term waterlogged samples was compared to archaeological oak dated at 13th century, and to pine dated at 17th century. Archaeological pine wood exhibits more intense degradation relative to the oak, even though the latter was 400 years older. Spectral analysis in the near-infrared range confirmed that amorphous and semi-crystalline regions of cellulose, hemicelluloses and lignin changed due to waterlogging. Conversely, the crystalline regions of cellulose seem not to be degraded.
Keywords: Cellulose; Lignin; Hemicellulose; Waterlogged wood; Degradation stage; Spectroscopy;
Poly(butylene azelate-co-butylene succinate) copolymers: Crystalline morphologies and degradation by A. Díaz; L. Franco; F. Estrany; L.J. del Valle; J. Puiggalí (80-91).
Random copolymers derived from 1,4-butanediol and two dicarboxylic units differing in the parity of the number of methylene groups and length of the polymethylene sequence (i.e. succinic and azelaic acids) were studied in terms of thermal properties, crystalline structure and morphology, crystallization kinetics and biodegradability.All samples were semicrystalline and their thermal properties varied in a wide temperature range. Copolymers crystallized according to the monoclinic α-form of polybutylene succinate and the orthorhombic structure postulated for polybutylene azelate depending on the predominant dicarboxylate unit. The behavior of the copolymer with an intermediate composition was complex due to strong dependence of the predominant crystalline form on crystallization and processing conditions. Interestingly, crystallization into the azelate structure was favored when samples were rapidly cooled from the melt, resulting in an unexpected increase in the degree of crystallinity. Spherulitic morphologies were clearly different (i.e. ringed spherulites and axialites) depending on the preferential crystalline structure.Enzymatic degradability of the two homopolyesters was highly different and could be enhanced by incorporation of comonomer units. Preferential enzymatic attack on amorphous regions highlighted the spherulitic morphologies of copolymers having well developed, distinctive ringed structures.
Keywords: Polyester; Random copolymers; Thermal properties; Spherulitic morphologies; X-ray diffraction; Enzymatic degradation;
Sol–gel derived architectures for enhancing cotton flame retardancy: Effect of pure and phosphorus-doped silica phases by Jenny Alongi; Claudio Colleoni; Giuseppe Rosace; Giulio Malucelli (92-98).
Pure and phosphorus-doped silica phases derived from sol–gel processes have been investigated, aiming to assess any enhancement of the thermal and fire stability of cotton fabrics. Indeed, it has already been shown that the combustion behaviour of cellulosic substrates can be strongly affected by the presence of a protective phosphorus-rich silica coating. Thus, in the present work, the performances of coatings consisting of pure silica and phosphorus-doped silica have been investigated and compared by using thermogravimetry and combustion tests (more specifically, resistance to an irradiative heat flux and to a flame application). The results show that the thermal and thermo-oxidative stability of cotton, as well its resistance to an irradiative heat flux of 35 kW/m2, have been enhanced by the deposited coating, irrespective of the presence of phosphorus. However, the best results have been achieved exploiting the joint effect of thermal shielding (exerted by the silica phase) and char-forming (as a consequence of the phosphoric acid source present in the alkoxysilane precursor). On the other hand, only pure silica coatings, despite their very low add-on, have proven to protect cotton from the application of a methane flame for 5 s, favouring the formation of a thermally stable residue.
Keywords: Sol–gel; Cotton; Thermal stability; Flame retardancy; Silica phases;
pH-controlled degradation and thermal stability of a porous poly(γ-glutamic acid) monolith crosslinked with an oxazoline-functionalized polymer by Sung-Bin Park; Junji Sakamoto; Moon-Hee Sung; Hiroshi Uyama (99-104).
A monolithic porous material designed for cell scaffolding applications has been introduced. A raw monolith with high surface area was prepared from a solution of poly(γ-glutamic acid) (PGA) by phase separation. The monolith was then crosslinked by using a low-toxic polymer that could be cleaved off from the monolith hydrolytically. The resultant monolith maintained the original porosity during the crosslinking process. It was also thermally stable up to decomposition temperature of PGA. The monolith was found to be low-cytotoxic and degradable in aqueous media at the rate controlled by the pH. The monolith was also found to adsorb/desorb a calcium salt by pH control, which may open up the possibility to change the surface nature of the monolith to promote cell adhesion and proliferation.
Keywords: Porous materials; Poly(γ-glutamic acid); Phase separation; Degradation; Cell scaffolds;
Catalyst-free synthesis of phosphinated poly(2,6-dimethyl-1,4-phenylene oxide) with high-T g and low-dielectric characteristic by Ching Hsuan Lin; Yi Jiun Tsai; Yu Sin Shih; Hou Chien Chang (105-110).
Phosphinated poly(2,6-dimethyl-1,4-phenylene oxide) (5–7) with various phosphorus contents were prepared through the bromination of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), followed by a catalyst-free nucleophilic substitution of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) on the resulting benzyl bromide of brominated PPO (2–4). Phosphinated PPOs showed improved solubility when compared with neat PPO. A phosphinated PPO with a T g at 227 °C (DMA data), T d 5% at 452 °C (N2) and 473 °C (air), low moisture absorption (0.7 wt% in boiling water, 48 h), a dielectric constant of 2.82 (1 GHz), and a UL-94 VTM-0 grade can be achieved with a phosphorus content as low as 1.0 wt%. Via this approach, the solubility and flame retardancy of PPO were enhanced while the thermal and dielectric properties were kept.Phosphinated poly(phenylene oxide)s (PPO) were successfully prepared by a two-step procedure including bromination and nucleophilic substitution. Via this approach, the solubility and flame retardancy of PPO were enhanced while the thermal and dielectric properties were kept.Display Omitted
Keywords: PPO; Bromination; Phosphinate; Low dielectric; Flame retardancy;
Caseins and hydrophobins as novel green flame retardants for cotton fabrics by Jenny Alongi; Riccardo Andrea Carletto; Francesca Bosco; Federico Carosio; Alessandro Di Blasio; Fabio Cuttica; Vincenza Antonucci; Michele Giordano; Giulio Malucelli (111-117).
Despite the use of toxic and not environmentally-friendly chemicals, some proteins derived from animal or microbial sources have been investigated as novel green flame retardants for cotton fabrics. In particular, phosphorus- and sulphur-rich proteins (i.e. caseins and hydrophobins) have been homogeneously deposited on cotton fabrics starting from protein aqueous suspensions/solutions. These surface treatments, based on the use of species able to favour the dehydration of cellulose instead of its depolymerization, have strongly enhanced the production of a thermally stable carbonaceous structure (char), hence significantly enhancing the flame retardancy of the fabrics, as assessed by thermogravimetry and flammability tests.
Keywords: Cotton; Green flame retardants; Caseins; Hydrophobins; Flammability; Combustion behaviour;
Study on flame retardancy of TGDDM epoxy resins loaded with DOPO-POSS compound and OPS/DOPO mixture by Wenchao Zhang; Xiangmei Li; Rongjie Yang (118-126).
The DOPO-POSS (polyhedral oligomeric silsesquioxane containing DOPO) and OPS/DOPO (octaphenyl polyhedral oligomeric silsesquioxane/DOPO) are used to flame retard the TGDDM/DDS (tetraglycidyl diamino diphenyl methane/4,4′-diaminodiphenylsulphone) resins. The blowing-out effect can be detected during the UL-94 tests of them. The LOI and UL-94 results indicate that DOPO-POSS or OPS/DOPO could make the LOI values of TGDDM/DDS resins greater than 34% and the UL-94 test reach V-0 rating. When keeping the same content of Si and P elements in the epoxy resins, the OPS/DOPO shows better flame retardancy and make the epoxy resins have better blowing-out intensity. The condensed phase and the gas products of TGDDM/DDS resins with DOPO-POSS and OPS/DOPO are investigated by the TGA, TGA–FTIR, SEM, FTIR and XPS. In the gas phase, DOPO-POSS and OPS/DOPO have negligible action on the gaseous product species of TGDDM/DDS resins. However, in the condensed phase, quite different performance of DOPO-POSS and OPS/DOPO can be observed. The good flame retardancy of the OPS/DOPO on the TGDDM/DDS resins is attributed to the matching between the melt viscosity and fast swelling, accumulation of the pyrolytic gases in the condensed phase, and fast and firm charring. Furthermore, the superabundant C–O-R structure in the condensed phase may be origin of the melt viscosity matching with melt swelling, and firm char during combustion.
Keywords: TGDDM; Flame retardancy; Blowing-Out; Condensed phase; POSS;
Influence of organically modified clays on the properties and disintegrability in compost of solution cast poly(3-hydroxybutyrate) films by D. Puglia; E. Fortunati; D.A. D'Amico; L.B. Manfredi; V.P. Cyras; J.M. Kenny (127-135).
Polymer nanocomposites, based on a bacterial biodegradable thermoplastic polyester, poly(hydroxybutyrate) (PHB), and unmodified montmorillonite Cloisite Na+ (CNa) and chemically modified Cloisite 15A and 93A (C15A and C93A), were prepared through a solution route. The nanostructure has been established through X-ray diffraction (XRD), while the nanocomposites were characterized by differential scanning calorimetry (DSC), contact angle measurements, and thermogravimetric (TGA) analysis. Disintegrability in composting conditions has been tested at certain times (0, 7, 14, 21, 28 and 35 days at 58 °C) and the effect of different nanoclays on the properties of biodegraded films was deeply investigated. XRD results suggest a better dispersion for C15A and C93A based nanocomposites that present also a more surface hydrophobic nature respect to PHB matrix and PHB nanocomposite loaded with unmodified Cloisite. This result is in accord with disintegrability behavior of PHB nanocomposites. Visual observation, chemical, thermal and morphological investigations proved that the disintegration in composting conditions was faster for PHB_4CNa respect to the systems loaded with modified clays suggesting the possibility to modulate the disintegrability capacity of PHB selecting a specific filler.
Keywords: Poly(hydroxybutyrate); Nanoclay; Organic modification; Nanocomposites; Disintegrability; Compost;
Linear and non-linear rheological characterization of photo-oxidative degraded LDPE by Víctor H. Rolón-Garrido; Manfred H. Wagner (136-145).
Sheets of low-density polyethylene (LDPE) were photo-oxidatively treated in the presence of air. Characterization methods include solvent extraction method and rheology in the melt state by shear and uniaxial extensional experiments. For photo-oxidation, a xenon lamp was used to irradiate the samples for times between 1 day and 6 weeks. Linear viscoelasticity is strongly affected by increasing photo-oxidation due to crosslinking of LDPE, as corroborated by gel fraction. For samples which were degraded for up to three days, negligible gel content was found and the non-linear parameters f max and β of the Molecular Stress Function (MSF) model indicate that the induced increase in strain hardening is due to the formation of long-chain branching, which is overcoming chain scission. Further degradation leads the parameter f max to increase to values outside the experimental window, while the parameter β was found to correlate with the gel content and with the trend followed by the strain hardening index. The competition between chain scission and crosslinking could also be followed in linear viscoelasticity by the change in activation energy and in the loss angle δ. From the constitutive analysis, it is noticed that, within the experimental window, time-deformation separability is confirmed for all samples, independent of the degree of photo-oxidation. It is demonstrated that the sensitivity of rheological characterization with respect to structural modifications, when combined with constitutive analysis, can be used to elucidate the effects of photo-degradation on LDPE.
Keywords: Rheology; MSF model; Strain hardening; Low-density polyethylene; Polymer melts; Photo-oxidative degradation;
Thermomechanical and hygroelastic properties of an epoxy system under humid and cold-warm cycling conditions by Jalal El Yagoubi; Gilles Lubineau; Shahid Saghir; Jacques Verdu; Abe Askari (146-155).
In this paper, we study the hygrothermal aging of an anhydride-cured epoxy under temperature and hygrometry conditions simulating those experienced by an aircraft in wet tropical or subtropical regions. Gravimetric and dimensional measurements were performed and they indicate that there are three stages in this aging process: the first one, corresponding to the early cycles can be called the “induction stage”. The second stage of about 1000 cycles duration, could be named the “swelling stage”, during which the volume increase is almost equal to the volume of the (liquid) water absorbed. Both the first and second stages are accompanied by modifications of the mechanical properties and the glass transition temperature. During the third (“equilibrium”) stage, up to 3000 cycles, there is no significant change in the physical properties despite the continuous increase of water uptake. This can be explained by the fact that only physically sorbed water can influence physical properties.
Keywords: Epoxy; Hygrothermal aging; Hydrolysis; Sorption;
Effect of modified cellulose fibres on the biodegradation behaviour of in-situ formed PMMA/cellulose composites in soil environment: Isolation and identification of the composite degrading fungus by Sunanda Sain; Shubhalakshmi Sengupta; Abhirupa Kar; Aniruddha Mukhopadhyay; Suparna Sengupta; Tanusree Kar; Dipa Ray (156-165).
Synthetic plastics like polyolefins, acrylics which are widely used in consumer products are not biodegraded by microorganisms in the environment. The accumulation of plastics in the environment becomes a matter of great concern leading to long-term environment, economic and waste management problems. In order to overcome these problems, significant attention has been given on biodegradable polymers, and also, on the identification of microorganisms with degrading potential upon polymeric materials. Therefore, recycling and biodegradation of these polymers is an important issue for environmental protection. The present work evaluates the effect of Maleic anhydride (MA) and Methylmethacrylate (MMA) modified cellulose micro and nano fibres (MACF and MMCF respectively) on the biodegradation behaviour of Polymethylmethacrylate (PMMA)/cellulose composites. MA and MMA modified cellulose reinforced PMMA composite granules were prepared by in-situ suspension polymerization technique. PMMA/cellulose composite films were prepared by solution casting method and the biodegradation behaviour of the films was studied by soil burial method in two types of soils (Soil A and Soil B). The biodegraded films were characterized by weight loss study, viscosity average molecular weights, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and Nuclear magnetic resonance spectroscopy (NMR). The isolation and identification of the fungus, which degraded these composites, were done for the first time along with the biodegradation study with the isolated pure culture.
Keywords: Biodegradation; Cellulose fibers; Scanning electron microscopy; Thermal analysis;
Continuous production of liquid reclaimed rubber from ground tire rubber and its application as reactive polymeric plasticizer by Jinwei Shi; Hua Zou; Linlin Ding; Xiaolin Li; Kuan Jiang; Tung Chen; Xiaodan Zhang; Liqun Zhang; Dongyun Ren (166-175).
Liquid reclaimed rubber (LRR) was produced from ground tire rubber (GTR) in a continuous operation by using a co-rotating twin-screw extruder. The effects of reclaiming recipe, screw configuration combination, barrel temperature, and screw speed on the degree of reclamation were investigated. Through the adjustment of these conditions, an LRR with a sol fraction of 73.5% was obtained. Characterizations of the LRR by gel-permeation chromatography (GPC), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and re-vulcanized ability tests showed that the LRR had unique properties – low viscosity, good compatibility with natural rubber (NR), and re-vulcanized ability. Because of these properties of LRR, it was used as reactive polymeric plasticizer in NR to replace the conventional oils such as the environmental aromatic oil (EAO) used in this study. The plasticizing effect, acetone extraction, mechanical properties, and thermostability of the LRR/NR compounds were investigated and compared with those of EAO/NR compounds. The results show that the plasticizing efficiency of LRR is somehow lower than that of EAO. In addition, the LRR-plasticized NR has higher tensile strength, modulus at 100% and 300% elongation, hardness, extraction resistance, and thermostability than EAO-plasticized NR.
Keywords: Co-rotating twin-screw extruder; Ground tire rubber; Liquid reclaimed rubber; Reactive polymeric plasticizer; Environmental aromatic oil;
Study of poly(vinylidene fluoride) radiative modification using core level spectroscopy by M.M. Brzhezinskaya; V.M. Morilova; E.M. Baitinger; S.E. Evsyukov; L.A. Pesin (176-179).
Modification of poly(vinylidene fluoride) (PVDF) directly during radiation exposure was investigated using core level spectroscopy. The strongly non-equilibrium condition of PVDF was studied. The high-resolved C K-edge NEXAFS spectra of poly(vinylidene fluoride) have been measured. The spectra modification due to the polymer degradation caused by monochromatic synchrotron radiation has been revealed. Residual fluorine content was monitored using x-ray photoelectron spectroscopy. The study has shown a significant modification of PVDF chemical content and electronic structure in the course of carbonization under synchrotron radiation. Gradual defluorination of the PVDF sample takes place during irradiation with enrichment of carbon skeleton with hydrogen. In the initial stages of radiative modification, defluorinated system is inhomogeneous and changes under the influence of two simultaneous processes: photochemical defluorination and diffusion of unbounded fluorine atoms to the sample surface.
Keywords: Polyvinylidene fluoride (PVDF); Radiative carbonization; NEXAFS spectroscopy; X-ray photoelectron spectroscopy;
Effect of low velocity impact responses on durability of conventional and nanophased CFRP composites exposed to seawater by Mohammad K. Hossain; Md. Mahmudur R. Chowdhury; Kazi A. Imran; Mahmud B. Salam; Arefin Tauhid; Mahesh Hosur; Shaik Jeelani (180-189).
The effect of nanoclay on the degradation of low velocity impact responses of carbon fiber reinforced polymer (CFRP) composites manufactured by the vacuum assisted resin transfer molding (VARTM) process is experimentally investigated with and without exposure to seawater for marine applications. Nanoclay was dispersed into the matrix by using magnetic stirring. Samples (100 mm by 100 mm) exposed to seawater for 0, 6, and 12 months in laboratory conditions were impacted at 20, 30, and 40 J energy levels using a Dynatup8210. The damage sustained by the samples was evaluated by a thermographic imaging technique. Comparisons between conventional and nanophased CFRP composites both in conditioned and unconditioned cases were made in terms of peak force, absorbed energy, deflection, delamination area, and specific delamination energy. Water absorption was observed to be reduced due to nanoclay infusion. After 12 months of exposure to seawater 2% nanophased samples absorbed 0.39% moisture whereas control samples absorbed 0.67% moisture. Impact strength, toughness, and energy absorption decreased with increasing conditioning time by weakening the bond between the fiber and matrix and softening the matrix materials. However, reduction in properties is significantly extenuated by the incorporation of nanoclay in the matrix. Specific delamination energy (SDE) is observed to be higher in the nanophased CFRP compared to that of the conventional one at different aging periods indicating enhanced fracture toughness in the nanophased composites. The larger and stronger interfacial area produced by the nanoclay inclusion has been found to facilitate more energy absorption in the nanophased sample compared to the conventional one. Furthermore, nanoclay reduced the development of delamination by arresting the crack propagation path or by toughening the matrix. It is concluded that the excellent barrier capacity, higher surface area, and high aspect ratio of nanoclay are responsible for the superior performance of CFRP composites, which in turn, enhances the durability of composites.
Keywords: Nanocomposite; Low velocity impact; Moisture absorption; Infrared thermography;
Photoyellowing revisited: Determination of an action spectrum of newspaper by Anu Heikkilä; Petri Kärhä (190-195).
Improved methodology for deriving action spectrum of photoyellowing induced by UV radiation on a polymeric material is reported. Facility designed and constructed for exposing materials with narrow-band UV radiation has been used for ageing newspaper samples for time periods of 1, 2, 4, and 8 h. Radiometric characterization of the facility has been utilized for defining the radiant exposure onto the samples during the exposures. Yellowing of samples has been quantified by post-exposure colour measurements. The relation between the quantified property change and the radiant exposure has been modelled. The analysis accounts for the logarithmic temporal behaviour of the property change and yields a generic material specific action spectrum for photoyellowing.
Keywords: Ultraviolet radiation; Photoyellowing; Action spectrum; Degradation;
Performance of PE pipes under extractive conditions: Effect of the additive package and processing by Dóra Tátraaljai; Mór Vámos; Ágnes Orbán-Mester; Peter Staniek; Enikő Földes; Béla Pukánszky (196-203).
Polyethylene (PE) compounds were prepared with five primary antioxidants and five application stabilizers, pelletized and extruded to pipes under industrial conditions. The pipes were stored in water at 80 °C for one year. Samples were taken at various intervals and a range of properties were determined from the functional group (methyl, vinyl, t-vinylene) content of the polymer to the crack propagation rate of the pipe. The results showed that chemical reactions take place both during extrusion and soaking. The chain structure of the polymer is modified only during processing, but not during storage, at least in the time scale of the study. The direction and extent of changes are determined mainly by the type of the application stabilizer, but primary antioxidants also influence them to some extent. Soaking modifies the physical, but not the chemical structure of the polymer. On the other hand, the chemical reactions of the additives determine color and stabilizer loss thus the residual stability of the pipes. The chemical structure of the polymer has a larger effect on final properties, on the rate of slow crack propagation and failure, than the physical structure of the pipes. As a consequence, the application stabilizer plays an important role in the determination of pipe performance.
Keywords: Polyethylene; Pipe; Antioxidant; Application stabilizer; Crack propagation;
Polystyrene- and poly (methyl methacrylate)-organoclay nanocomposites using a one-chain benzimidazolium surfactant by Guipeng Cai; Jianxiang Feng; Jin Zhu; Charles A. Wilkie (204-210).
In this paper, the synthesis of a one-chain benzimidazolium surfactant is accomplished and polystyrene (PS) and poly(methyl methacrylate) (PMMA) nanocomposites with organoclay modified by the above surfactant are prepared by melt blending. XRD, TEM, TGA and cone calorimetry are employed to evaluate the dispersion of the clay in the polymer matrices, thermal stability and fire behavior. TEM results show that the clay disperses more uniformly in the PMMA matrix than in PS. Both polymer nanocomposites exhibit enhanced thermal stability. From cone calorimetry, substantial reduction of heat release rates is obtained at 3wt% and 5wt% of clay from polystyrene and a more remarkable reduction in PMMA.
Keywords: Polymer nanocomposites; Fire retardancy; Benzimidazolium; Dispersion;
Investigation of basic zinc cyanurate as a novel thermal stabilizer for poly(vinyl chloride) and its synergistic effect with calcium stearate by Xiaopeng Xu; Si Chen; Wei Tang; Yingjun Qu; Xu Wang (211-218).
Basic zinc cyanurate (Zn3(C3N3O3)2·ZnO, represented as Zn3Cy2) was synthesized via a precipitation method, and investigated as a thermal stabilizer for poly(vinyl chloride) (PVC) by thermogravimetric analysis (TGA), Congo red test and discoloration test. The thermal stability of PVC was significantly enhanced with the addition of Zn3Cy2. Compared with zinc stearate (ZnSt2), it is observed a significant improvement that Zn3Cy2 could delay the “zinc burning” of PVC. This is attributed to the strong ability of the cyanurate anions in Zn3Cy2 to absorb the hydrogen chloride released by the degradation of PVC. Moreover, mixing Zn3Cy2 with calcium stearate (CaSt2) in different mass ratios greatly promoted the thermal stability of PVC. Excellent synergistic effects could be observed when CaSt2/Zn3Cy2 combined with some commercial auxiliary stabilizers. Addition of dibenzoylmethane (DBM) brought a remarkable increase in initial color for PVC containing CaSt2/Zn3Cy2 while epoxidized soybean oil (ESBO) could improve both initial color and long-term stability.
Keywords: Poly(vinyl chloride); Thermal stabilizer; Basic zinc cyanurate; Dibenzoylmethane; Epoxidized soybean oil; Synergistic effect;
Effects of gamma rays and neutron irradiation on the glucose response of boronic acid-containing “smart” hydrogels by Jules Magda; Seung-Hei Cho; Seth Streitmatter; Tatjana Jevremovic (219-222).
If a biomaterial is to be implanted in the body, it must be subjected to a sterilization procedure which often involves gamma irradiation. We report results for the effects of γ-irradiation on the glucose response of a hydrogel with glucose-binding boronic acid moieties. This ‘smart” hydrogel is of a type suitable for use in non-enzymatic glucose sensors. In addition, the effect of neutron irradiation on the glucose response of these hydrogels is also of interest, because the hydrogels could be used with minor modification to deliver boron to tumors during boron neutron capture therapy (BNCT). We show that the glucose response of the smart hydrogels is unaffected by exposure to neutrons in the dose range typical for BNCT. The effect of gamma rays on the glucose response depends on the method used to cure the smart hydrogel. If the hydrogel is cured with a thermal free-radical-initiator, then the hydrogel can be sterilized by gamma irradiation with no adverse effects upon the glucose response. However, if the hydrogel is cured with a UV-initiated free radical initiator, then the glucose response decreases in magnitude with increase in the gamma radiation dose.
Keywords: Hydrogels; Gamma rays; Stimuli-responsive; Boron neutron capture therapy; Nuclear reactor; Glucose;
Desorption electrospray ionisation mass spectrometry of stabilised polyesters reveals activation of hindered amine light stabilisers by Martin R.L. Paine; Ganna Gryn'ova; Michelle L. Coote; Philip J. Barker; Stephen J. Blanksby (223-232).
The use of hindered amine light stabilizers (HALS) to retard thermo- and photo-degradation of polymers has become increasingly common. Proposed mechanisms of polymer stabilisation involve significant changes to the HALS chemical structure; however, reports of the characterisation of these modified chemical species are limited. To better understand the fate of HALS and determine their in situ modifications, desorption electrospray ionisation mass spectrometry (DESI-MS) was employed to characterise ten commercially available HALS present in polyester-based coil coatings. TINUVIN® 770, 292, 144, 123, 152, and NOR371; HOSTAVIN® 3052, 3055, 3050, and 3058 were separately formulated with a pigmented, thermosetting polyester resin, cured on metal at 262 °C and analysed directly by DESI-MS. High-level ab initio molecular orbital theory calculations were also undertaken to aid the mechanistic interpretation of the results. For HALS containing N-substituted piperidines (i.e., N–CH3, N–C(O)CH3, and N–OR) a secondary piperidine (N–H) analogue was detected in all cases. The formation of these intermediates can be explained either through hydrogen abstraction based mechanisms or direct N–OR homolysis with the former dominant under normal service temperatures (ca. 25–80 °C), and the latter potentially becoming competitive under the high temperatures associated with curing (ca. 230–260 °C).
Keywords: Mass spectrometry; Polyester; Hindered amine light stabiliser; Mechanism;
Study on thermal degradation kinetics of cellulose-graft-poly(l-lactic acid) by thermogravimetric analysis by Lin Dai; Lu-Ying Wang; Tong-Qi Yuan; Jing He (233-239).
The thermal degradation of cellulose-graft-poly(l-lactic acid) at different heating rates in nitrogen was studied by thermogravimetric analysis (TGA) in the temperature range 20–550 °C. Nuclear magnetic resonance (NMR), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC) analyses were utilized to determine the microstructure and glass transition temperature of cellulose-graft-poly(l-lactic acid). The kinetic parameters were determined by using Friedman, Flynn–Wall–Ozawa, and Kissinger methods. Coats–Redfern method was used to investigate the probable degradation mechanism. The results indicated that the trend of activation energy of cellulose-graft-poly(l-lactic acid) increases with increasing the content of the poly(l-lactic acid) and the process of the non-spontaneous degradation stage, goes to a random nucleation with two nuclei on the individual particle mechanism, whose rate-controlling process could be described by conversion rate (α) (integral form 1/(1 − α)).
Keywords: Cellulose; Poly(l-lactic acid); Thermogravimetric analysis; Degradation mechanism; Kinetic parameter;
The non-isothermal degradation kinetics of St–MMA copolymers by Hamid Reza Azimi; Mostafa Rezaei; Faezeh Majidi (240-248).
Styrene–methyl methacrylate (St–MMA) random copolymer in different compositions, polystyrene (PS) and polymethyl methacrylate (PMMA) particles were synthesized by suspension polymerization. The copolymer compositions were determined using nuclear magnetic resonance (H NMR) method as well as their molecular weights were examined by gel permeation chromatography (GPC). The non-isothermal degradation behavior of the synthesized copolymers was studied by thermal gravimetric analysis (TGA) under nitrogen purge and the results were compared with corresponding homopolymers. In this study it was tried to clarify the effect of St–MMA copolymer composition on the non-isothermal degradation kinetics. It was found that with decreasing the MMA content in copolymer, the molecular weight was decreased and degradation temperature in copolymer increased in all heating rates. The activation energy was calculated by the Flynn–Wall–Ozawa method. It was concluded that using the model fitting methods couldn't reveal the complexity of the thermal degradation process and the model-free methods could be a reliable way to determine the kinetic parameters. Furthermore the iso-kinetic relationship (IKR) was used to estimate a model independent pre-exponential factor (lnA) corresponding to a given degree of conversion.
Keywords: St–MMA; Copolymer composition; PS; PMMA; Degradation kinetics;
Metathetic degradation of trans-1,4-polyisoprene with ruthenium catalysts by Samira Ouardad; Frédéric Peruch (249-253).
Degradation study of trans-1,4-polyisoprene (trans-1,4-PI), that can be produced by the nature, was performed using first and second generation Grubbs and Hoveyda–Grubbs catalysts with olefins (ethylene or 1-octene) as transfer agents in toluene at 60 °C. While first generation Grubbs catalyst afforded low degradation, highlighting the presence of catalyst decomposition and/or inter-chain cross-metathesis reactions, an almost complete metathetic degradation could be reached using the second generation Grubbs catalyst in few minutes. Nevertheless, the synthesis of well-defined polyisoprenes with a targeted molar mass revealed to be difficult with Grubbs catalysts. On the contrary, Hoveyda–Grubbs catalysts were found to be more efficient to control the degradation of trans-1,4-PI. Indeed, regioselective degradation afforded pure trans-1,4-PI with a range of molar mass from 50 000 g/mol to 10 000 g/mol. However, polyisoprenes of lower molar masses (M n < 10 000 g/mol) contained some cis units, highlighting the presence of isomerization reactions, which could be due to the catalyst decomposition into hydride specie and/or π-allyl metal hydride.
Keywords: Metathetic degradation; Trans-1,4-polyisoprene; Ruthenium catalysts; Ethylene; Octene;
Limits in the validity of Arrhenius predictions for field ageing of a silica filled polychloroprene in a marine environment by V. Le Saux; P.Y. Le Gac; Y. Marco; S. Calloch (254-261).
Accelerated ageing in natural sea water at different temperatures from 20 °C to 80 °C was performed on a silica filled polychloroprene rubber. Degradation when monitored with mechanical properties at both macroscopic and microscopic scale led to a large increase of the modulus coupled with a strong decrease of strain and stress at break. Data from tensile tests were used for lifetime prediction with an Arrhenius extrapolation for modulus, strain and stress at break. The validity of this lifetime prediction was evaluated using a 23 year-old sample aged in natural conditions. Strain at break could be predicted using an Arrhenius extrapolation with an activation energy of 50 kJ/mol. However, an extrapolation based on linear Arrhenius behaviour did not apply for modulus and stress at break due to the presence of a degradation profile across the sample. These observations confirmed that strain at break is not governed by bulk properties of samples but by the degradation rate at the external surface of the sample (i.e. in contact with water).
Keywords: Polychloroprene rubber; Accelerated and natural ageing tests; Arrhenius extrapolation; Lifetime prediction; Sea water;
Comprehensive two-dimensional gas chromatography for determining the effect of electron beam treatment of polypropylene used for food packaging by Maurus Biedermann; Roberto Castillo; Anne-Marie Riquet; Koni Grob (262-273).
The performance of comprehensive two-dimensional gas chromatography (GC × GC) was investigated for the analysis of compounds of potential regulatory concern in polypropylene (PP) films before and after treatment by electron beams. The detection limit was at 0.1 mg/kg film, deduced from the regulatory threshold of concern and an assumed high migration. GC × GC enables the detection of minor components without prior removal of the dominating saturated hydrocarbons. Owing to the sharp peaks in the second dimension GC, the detection limit is reached even by flame ionization detection, which is the technique of choice for quantitative estimates without calibration of the response. Time of flight (TOF) mass spectrometry (MS) was used to obtain spectra for peak identification. Optimized GC × GC involved a polar (50% phenyl methyl polysiloxane) for the first dimension separation and a methyl polysiloxane for the second. Electron beam (EB) treatment produced many degradation products from the additives as well as from the polymer.
Keywords: Migration from FCM; Comprehensive analysis; Degradation products; Irgafos 168; Irganox 1076;
The mechanical properties, biocompatibility and biodegradability of chestnut shell fibre and polyhydroxyalkanoate composites by Chin-San Wu; Hsin-Tzu Liao (274-282).
The mechanical properties, biocompatibility and biodegradability of composite materials made from chestnut shell fibre (CSF) and poly(hydroxyalkanoate) (PHA), as well as CSF and glycidyl methacrylate-grafted PHA (PHA-g-GMA), were evaluated. Composites formed from PHA-g-GMA/CSF were found to have noticeably superior mechanical properties compared with those of PHA/CSF. CSF could be homogeneously dispersed in the PHA-g-GMA matrix as a result of condensation reactions. Human foreskin fibroblasts (FBs) were seeded on these two series of composites to characterise the biocompatibility properties. FB proliferation and collagen production on the PHA/CSF series of composites were superior to that on the PHA-g-GMA/CSF composites. PHA-g-GMA/CSF was found to be more water resistant than PHA/CSF, although the weight loss of both composites buried in Rhizobium radiobacter compost indicated that both were biodegradable, especially at high levels of CSF substitution. Furthermore, the PHA/CSF and PHA-g-GMA/CSF composites were more biodegradable than pure PHA.
Keywords: Poly(hydroxyalkanoate); Chestnut shell fibre; Biocompatibility; Biodegradation;
Effect of water vapor in air on thermal degradation of paper at high temperature by Emilia Vänskä; Minna Luukka; Iina Solala; Tapani Vuorinen (283-289).
Thermal degradation of lignocellulosic materials has been studied widely because of its importance in several applications. While a variety of thermal treatment setups has been proposed, this paper introduces a thermal treatment method where high temperature is combined with presence of water vapor in an atmospheric oven chamber. The performance of the device was evaluated at temperature and volume fraction of water vapor ranges of 175–300 °C and 1–98%, respectively. The impact of the treatment was assessed by observing the changes in paper sheets, specifically brightness, light absorption coefficient, burst strength, ultraviolet resonance Raman spectra and the degree of polymerization of cellulose. The results demonstrated that the adapted thermal treatment device functions within the tested ranges of temperature and volume fraction of water vapor. In this study water vapor was found to accelerate hydrolytic thermal degradation of fully bleached paper sheets in terms of thermal yellowing and strength deterioration. In contrast, the empirical findings with lignin-containing paper provided new information on how the residual lignin increases its resistance towards water vapor introduced thermal degradation. This was demonstrated by the results of ultraviolet resonance Raman spectra and light absorption coefficient, which suggested that the thermal degradation of lignin is substantially enhanced in the presence of oxygen.
Keywords: Brightness; Cellulose; Lignin; Paper; Thermal degradation; Water vapor;
Phenomenological and chemomechanical modeling of the thermomechanical stability of liquid silicone rubbers by A. Mlyniec; A. Morawska-Chochol; K. Kloch; T. Uhl (290-297).
In this article, we present the constitutive models taking into account the stability of liquid silicone rubber's. We propose the phenomenological large strain viscoelastic material model and the enhanced chemomechanical model. The phenomenological model is calibrated to the experimental investigations probing the thermomechanical behavior of liquid silicone rubber's, while the chemomechanical model uses kinetic theory, to calculate the changes of mechanical properties in time. The proposed chemomechanical model employs: chemical reaction kinetics, statistical mechanics and microstructural based Bergström-Boyce material model. Viscoelastic material property changes resulting from e.g. the variation of crosslink density are computed using the Arrhenius equation. The material model is validated by comparison with results of compression tests of specimens aged in 125 and 175 °C non-loaded and under stress of 0.48 MPa. We achieve 96% compliance for investigated temperature and pressure range. The good agreement with the experimental data, demonstrates that chemomechanical modeling framework provides a useful tool for the prediction of the stability of liquid silicone rubbers and the lifetime of vibration isolators.
Keywords: Chemical degradation; LSR aging; Service life modeling; Molecular based model; Stability of LSR; Modeling of degradation;
Study on the change of silicon and phosphorus content in the condensed phase during the combustion of epoxy resin with OPS/DOPO by Wenchao Zhang; Xiangmei Li; Rongjie Yang (298-303).
The residues at different time and position of epoxy resin (EP) were obtained during the cone calorimeter tests. The change of Si and P content in these residues during the combustion was obtained by XPS analysis. The result indicates that the Si content reduces at the beginning of fire and the Si element will accumulate with development of fire. These are caused by that, at the beginning of fire, the molten fragment of EP matrix will move upwards and accumulate, but the Si element does not. With development of fire, the product of interaction between the fragment of OPS and decomposition product of EP begins to migrate upwards and accumulate at the surface. However, the P-containing compounds directly migrated upward with the degradation products. The chemical structures of Si-containing and P-containing compounds during the combustion were investigated by the FTIR and XPS. The interactions between DOPO and OPS in the condensed phase happened during the migration process of Si-containing and P-containing compound in the combustion of EP.
Keywords: Epoxy resin; Silicon; Phosphorus; Condensed phase; XPS;