Polymer Degradation and Stability (v.122, #C)
Editorial Board (IFC).
Water-soluble polyelectrolyte complex nanocoating for flame retardant nylon-cotton fabric by Marcus Leistner; Merid Haile; Sarah Rohmer; Anas Abu-Odeh; Jaime C. Grunlan (1-7).
Blends of cotton with synthetic fibers are widely used for various military and industrial applications. Nylon-cotton (NYCO) blends offer high durability and strength from nylon and the softness of cotton, but both fiber types are highly flammable. Previously reported flame retardant coatings for cotton fabric, comprised of a complex of polyethylenimine and a polyphosphate, are not able to protect NYCO textiles, so a new generation of water-soluble polyelectrolyte complex coating is needed. The basis of this new treatment is an aqueous complex of polyethylenimine and ammonium polyphosphate that forms melamine polyphosphate in-situ during exposure to a melamine-containing solution. NYCO fabric was rendered self-extinguishing in a vertical flame test and pyrolysis combustion flow calorimetry showed a 28% reduction in total heat release, and a 65% reduction of cotton's peak heat release, with less than 20 wt% coating. The effectiveness of this halogen-free, flame retardant coating is due to condensed phase activity that includes cooling effects and charring. The ease of this coating procedure and the use of more environmentally benign chemicals deposited from aqueous solutions make this an industrially feasible alternative to current treatments.
Keywords: Flame retardant; Nylon-cotton fabric; Melamine polyphosphate; Nanocoating; Combustion calorimetry;
Synthesis and characterization of aluminum poly-hexamethylenephosphinate and its flame-retardant application in epoxy resin by Jingyu Wang; Lijun Qian; Bo Xu; Wang Xi; Xinxin Liu (8-17).
A flame retardant additive, aluminum poly-hexamethylenephosphinate (APHP) with a polymeric structure was synthesized from 1,5-hexadiene, hypophosphorous acid and aluminum ions. The molecular structure of APHP and thermal stability were characterized by solid nuclear magnetic resonance, Fourier transform infrared and thermogravimetric analysis. Then, APHP was applied into diglycidyl ether of bisphenol-A cured by 4,4′-diamino-diphenylmethane. APHP showed flame-retardant effect on the epoxy thermosets in limited oxygen index (LOI), UL94 vertical test and cone calorimeter. The thermosets with only 4 wt.% APHP obtained an LOI value of 32.7% and reached the UL94 V-1 rating. The APHP/EP thermosets decreased the pk-HRR, THR and av-EHC values, decreased CO2Y and enhanced the COY ratios, and also reserved more residual char comparing with neat thermoset. The less incorporation of APHP in thermosets will impose the better flame retardancy to epoxy thermosets. The flame-retardant effect of APHP was resulted by its two main pyrolyzed contents phosphorus and alkyl-phosphinic fragments. In condensed phase, the phosphorus-containing contents facilitated to the higher char yields and the formation of intumescent char layer, which led to a reduction of the released fuel and a strong barrier effect to weaken the combustion intensity. In gas phase, the PO, PO2 and alkyl-phosphinic fragments with quenching effect were released from the phosphorus-containing contents, and can decrease the heat release and weaken the combustion intensity.
Keywords: Flame retardant; Phosphinate; Epoxy resin; Alkyl-phosphinate;
Polymeric flavonoids processed with co-polymers as UV and thermal stabilisers for polyethylene films by James H. Bridson; Jasneet Kaur; Zhenhua Zhang; Lloyd Donaldson; Alan Fernyhough (18-24).
Stabilisers are often required to extend the service life of polymers, however few bio-based options are available. The effect of polymeric flavonoids, processed with co-polymers, on the thermal and UV stability of polyethylene films was investigated. Condensed tannin extracts from Pinus radiata and Acacia mearnsii were compounded with a range of co-polymers into linear low density polyethylene films. Tannin compatibility with the polymer matrix was studied using confocal microscopy. The thermal and UV stability was assessed using differential scanning calorimetry, accelerated weathering, mechanical testing and infrared spectroscopy. Tannin increased the thermo-oxidative stability of the films, particularly when the compatibility was enhanced using co-polymers. Furthermore, tannin improved the UV stability during accelerated weathering, with greater strength and elongation retention. The stability provided by tannin may be attributed to radical scavenging by the chain breaking donor mechanism. These results show potential for tannin as a stabiliser for polyethylene, however further improvements in performance need to be achieved to facilitate commercial uptake.
Keywords: Polyethylene; Flavonoid; Condensed tannin; Stabiliser; Accelerated weathering;
The synergistic effect of zinc oxide and phenylphosphonic acid zinc salt on the crystallization behavior of poly (lactic acid) by Peng Chen; Hongfu Zhou; Wei Liu; Min Zhang; Zhongjie Du; Xiangdong Wang (25-35).
In order to improve the crystallinity and crystallization rate of poly (lactic acid) (PLA), a method for the preparation of a composite nucleating agent (CNA) consisting of zinc oxide and phenylphosphonic acid zinc salt was proposed. Zinc oxide, phenylphosphonic acid zinc salt and CNA were mixed into PLA through the melt blending method, respectively. The resultant PLA samples were characterized by differential scan calorimeter (DSC) and polarized optical microscope (POM). The DSC results showed that the crystallinity and crystallization temperature of the PLA samples with CNA were higher than those of the other PLA samples. The phenomena of crystallization nucleation and growth of various PLA samples were observed by means of POM. Isothermal and non-isothermal crystallization behavior of various PLA samples with different addition of CNA was studied, the corresponding result showed that the overall crystallinity, crystallization rate, nucleation density, and spherulite number increased obviously, as well as the crystallization time decreased, indicating the heterogeneous nucleating effect of CNA on the crystallization of PLA. For each of the component of CNA, the phenylphosphonic acid zinc salt could be used as an effective site of heterogeneous nucleation, resulting in the increasing nucleation density of PLA, and the zinc oxide could be acted as a good crystallization promoter for promoting the crystal growth of PLA. At the CNA content of 1 phr, CNA had a significant impact on crystallization behavior of PLA with a little negative influence on the molecular weight of PLA.
Keywords: Synergistic effect; Poly(lactic acid); Phenylphosphonic acid zinc salt; Zinc oxide; Composite nucleating agent; Crystallization kinetics;
Addition flame-retardant behaviors of expandable graphite and [bis(2-hydroxyethyl)amino]-methyl-phosphonic acid dimethyl ester in rigid polyurethane foams by Wang Xi; Lijun Qian; Yajun Chen; Jingyu Wang; Xinxin Liu (36-43).
The flame-retardant rigid polyurethane foams (RPUFs) with [bis(2-hydroxyethyl)amino]-methyl-phosphonic acid dimethyl ester (BH)/expandable graphite (EG) were prepared via box-foaming in our laboratory. The flame retardancy of RPUFs with BH and EG was characterized using the limiting oxygen index (LOI), cone calorimeter test. The results show that BH/EG system obviously increased the LOI value, decreased the heat release rate and mass loss rate, and enhanced the char yields of RPUFs. The results reveal that the addition flame-retardant effects from BH and EG. The flame-retardant mechanism of RPUFs was also detected using scan electronic microscopic and pyrolysis-gas chromatography/mass spectroscopy. According to the test results, BH promoted forming the firm phosphorus-containing char layer, which adhered the loose and worm-like expanded graphite in condense phase. Then, the compacter and thicker char layer was obtained. It will exert well obstructing property to fire in condensed phase. Moreover, BH also will generate dimethyl methylphosphonate (DMMP) gas and then be pyrolyzed to PO and PO2 free radicals in gaseous phase during combustion, which can quench the flammable free radicals from the matrix and terminate the free radical chain reaction of combustion. After the combination of the bi-phase flame-retardant effects, BH/EG flame-retardant system brought addition flame-retardant effects, and thus providing the better flame retardancy to matrix than one of them does. Moreover, the results of compressive strength, thermal conductivity and apparent density reveal that BH/EG/RPUF can meet the demand for the application in reality.
Keywords: Flame retardant; Addition flame-retardant effect; PU; EG;
Highly effective flame retarded epoxy resin cured by DOPO-based co-curing agent by Weihua Xu; Alvianto Wirasaputra; Shumei Liu; Yanchao Yuan; Jianqing Zhao (44-51).
A highly effective 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based flame retardant (D-bp) was successfully synthesized via the addition reaction between DOPO and Schiff-base obtained in advance by the condensation of 4,4’-diaminodiphenyl methane (DDM) and 4-hydroxybenzaldehyde. D-bp was used as co-curing agent to improve the flame retardancy of DDM/diglycidyl ether of bisphenol A (DGEBA) system. Non-isothermal curing kinetics, thermal and flame-retardant properties of cured epoxy resins were studied by differential scanning calorimeter (DSC), thermogravimeric analysis (TGA), UL94 vertical burning test, limited oxygen index (LOI) and cone calorimeter test. The morphology of residues after cone calorimeter test was observed by scanning electron microscope (SEM). The results revealed that the epoxy thermosets exhibited excellent flame-retardancy and passed V-0 rating of UL 94 test with LOI of 39.7% when the phosphorus content was only 0.5 wt%.
Keywords: Flame retardancy; Epoxy resin; DOPO derivative; Crosslink density; High efficiency;
Guaran-based biodegradable and conducting interpenetrating polymer network composite hydrogels for adsorptive removal of methylene blue dye by Reena Sharma; Susheel Kalia; Balbir S. Kaith; Deepak Pathania; Amit Kumar; Pankaj Thakur (52-65).
Microwave initiated grafting of itaconic acid was carried out on guaran polysaccharide to get a crosslinked network of guaran–itaconic acid. Different reaction parameters were optimized for the graft copolymerization of itaconic acid on guaran to get the candidate polymer with maximum percentage swelling. Conducting interpenetrating polymer network (IPN) was prepared by aniline absorption in the semi-IPN network by two-step aqueous polymerization. Crosslinked structure was characterized by Fourier transform infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Biodegradation of synthesized hydrogels was studied by soil burial and composting methods and monitored by FTIR and SEM techniques. Conducting interpenetrating polymer network composite hydrogels were studied for the adsorptive removal of methylene blue dye. Pseudo first and pseudo second order kinetics models were used to describe the adsorption kinetics of dye removal.
Keywords: Guaran; Swelling; Biodegradation; Dye adsorption; Adsorption kinetics;
Novel crosslinkable epoxy resins containing phenylacetylene and azobenzene groups: From thermal crosslinking to flame retardance by Bo-Wen Liu; Hai-Bo Zhao; Yi Tan; Li Chen; Yu-Zhong Wang (66-76).
Several kinds of novel flame-retardant-free and thermo-crosslinkable epoxy resins (EPs) containing azobenzene or/and phenylacetylene groups have been synthesized and characterized, and the flame retardant properties as a result of thermal crosslinking during combustion were investigated in detail. Crosslinking behaviors were tested by simultaneous thermogravimetry–differential scanning calorimetry (TGA–DSC). Thermal stabilities were investigated by thermogravimetric analysis (TGA). Flame retardance of the resulting EPs was evaluated through LOI tests, and combustion behaviors were studied via cone calorimetry and micro-combustion calorimetry (MCC), which further confirmed that flame retardance of these EPs was significantly improved, despite the absence of conventional flame retardant. Py–GC/MS analysis was used to investigate the degradation mechanism of these epoxy resins, and the results confirmed that the flame-retardant activity of epoxy resins mainly took effect in the condensed phase. The chemical constitution of the char layers were investigated by XPS and Raman spectrum. The co-crosslinking behavior between azobenzene and phenylacetylene groups was predicted and confirmed, which led to the most compact char layer, therefore resulted in the best flame retardance of these EPs.
Keywords: Epoxy resin; Crosslinking; Flame retardance; Carbonization;
The degradation of poly(trimethylene carbonate) implants: The role of molecular weight and enzymes by Liqun Yang; Jianxin Li; Wei Zhang; Ying Jin; Jinzhe Zhang; Yan Liu; Dongxu Yi; Miao Li; Jing Guo; Zhongwei Gu (77-87).
The degradation of poly(trimethylene carbonate) (PTMC) implants with different molecular weights was investigated in vitro and in vivo. The results showed that PTMC degraded in vitro enzymolysis case and in vivo via surface erosion. The effect of the molecular weight on the degradation rate of PTMC was investigated in light of hydrophilicity and form-stability. A higher degradation rate was seen in the high molecular weight PTMC and its more hydrophobic surface with better form-stability. Furthermore, PTMC had a higher degradation rate of in vitro enzymolysis because of the surfactants role of lipase in diffusion of the degradation products. The results indicate that the form-stabilized PTMC is a promising candidate for clinical subcutaneous implants especially due to their tunable degradation rate.
Keywords: Poly(trimethylene carbonate); In vitro degradation; In vivo implantation; Molecular weight; Lipase; Form-stability;
Novel organo-modifier for thermally-stable polymer-layered silicate nanocomposites by N.Tz. Dintcheva; S. Al-Malaika; E. Morici (88-101).
A new novel approach for the stabilisation of polymer-clay nanocomposites has been investigated based on reacting chemically an antioxidant function, a hindered phenol moiety, with an organic modifier based on a quaternary ammonium salt. The chemically linked antioxidant-containing organic modifier (AO-OM) was then introduced into natural montmorillonite (MMt) through a cation-exchange reaction resulting in antioxidant-containing organo-modified clay (AO-OM-MMt). The new antioxidant-containing modified clay, along with other organo-modified clays having a similar organo-modifier but without the reacted antioxidant, were characterised by spectroscopic, thermogravimetric and x-ray diffraction techniques and tested for their thermo-oxidative stability.PA11-based clay nanocomposites samples containing the AO-OM-MMt and the other organo-modified clays, both without and with an added (i.e. not chemically reacted) hindered phenol antioxidant (similar to the one used in the AO-OM) were prepared by melt processing and examined for their processing and long-term thermal-oxidative stability at high temperatures. It was shown that although the new organo-modifier, AO-OM, was also susceptible to the Hoffman elimination reaction, the nanocomposites containing this newly modified clay (PA11/AO-OM-MMt) showed higher melt processing and long-term thermo-oxidative stability, along with excellent clay dispersion and exfoliation, compared to the other PA11-nanocomposites examined here (with and without the conventionally added antioxidant). It is suggested here that the excellent overall performance observed for the PA11/AO-OM-MMt nanocomposites is due to an in-situ partial release of low molecular weight antioxidant species having stabilising functionalities that are capable of acting locally at the interface between the inorganic clay platelets and the polymeric matrix which is a critical area for the onset of degradation processes.
Keywords: Polymer-clay nanocomposites; PA11; Antioxidant-containing organomodifier; Modified montmorillonites;
Synthesis, mechanical properties and fire behaviors of rigid polyurethane foam with a reactive flame retardant containing phosphazene and phosphate by Rong Yang; Wentian Hu; Liang Xu; Yan Song; Jinchun Li (102-109).
Reactive flame retardant hexa-(phosphite-hydroxyl-methyl-phenoxyl)-cyclotriphosphazene (HPHPCP) was synthesized by hexachlorocyclotriphosphazene, diethyl phosphite and p-hydroxybenzaldehyd. Flame retardant rigid polyurethane foams (FR-RPUFs) were prepared by free foaming with incorporating HPHPCP with polyether polyol, polyester polyol and polymethylene polyphenyl isocyanate. The chemical structure of HPHPCP was characterized by proton and 31P nuclear magnetic resonance. The morphology, physical–mechanical properties, thermal stability and flame-retardant performance of rigid polyurethane foam (RPUF) and FR-RPUFs were investigated. Results suggested that the incorporation of HPHPCP into RPUF enhance the density, comprehensive strength and thermal stability as a result of higher crosslink concentration resulting from the multifunctional group of HPHPCP. Furthermore, with the increase of HPHPCP content, the limiting oxygen index (LOI) increased along with the gradually decreased values of the second peak heat release rate (PHRR2). In addition, when the additive of HPHPCP was higher than 10 wt%, FR-RPUFs pass UL-94 HF-1 rating and the flame spread limited simultaneously, indicating the reinforced and flame-retardant RPUFs could be obtained.
Keywords: Rigid polyurethane foam; Flame retardant; Synthesis; Fire behavior;
A study of the degradation of polymers irradiated by Cn+ and On+ 9.6 MeV heavy ions by R. Mikšová; A. Macková; P. Malinský; P. Slepička; V. Švorčík (110-121).
Polypropylene (PP), polyethyleneterephthalate (PET), polycarbonate (PC) and poly(ether–ether–ketone) (PEEK) foils were irradiated with 9.6 MeV Cn+ and On+ ions at fluences of 1010–1013 cm−2 simultaneously with heavy-ion energy-loss experiments and energy straggling measurements in polymers. Structural and compositional changes of the polymers after the irradiation are very important for the estimation of these effects in connection with the experimentally determined ion energy losses. Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) were used for elemental composition study, whereas UV–visible spectrum study (UV–Vis) and Fourier transformation infrared spectroscopy (FTIR) were utilised to follow the structural changes (polymeric functional group appearance, double bonds, carbon-cluster creation etc.) of the irradiated polymers. Heavy-ion irradiation causes a release of hydrogen and oxygen from the polymers penetrated by the ion beam, chemical and structural changes, the new appearance of radicals, and polymeric-chain cross-linking especially at ion fluences above 1012–1013 cm−2. The compositional and structural changes related to the ion species, ion-irradiation fluence and the type of polymer were studied and discussed in connection with the energy-loss measurement.
Keywords: Energy loss; Heavy ions; Polymers; RBS/ERDA methods; AFM method;
Recycling of blends made of polypropylene and an iron-based oxygen scavenger – Influence of multiple extrusions on the polymer stability and the oxygen absorption capacity by Markus Lehner; Daniel Schlemmer; Sven Sängerlaub (122-132).
An often used oxygen scavenger is a blend of iron powder and additives dispersed in a polymer carrier matrix. It is applied as an additive for separate layers of multilayer film structures which are produced by coextrusion. Not much is known about the influence of multiple extrusions, for example during recycling processes, of these materials on polymer properties, film properties and process stability. Therefore the aim of this study was to assess these issues. The focus was on polypropylene because it is a common blend partner for iron-based oxygen scavenger additives. Pure polypropylene and blends of polypropylene with approximately 20 wt.-% iron-based oxygen scavenger additive (SHELFPLUS® O2 2710) were extruded up to ten times at two temperature profiles (T1: 160–230 °C; T2: 210–300 °C). Polymer degradation was evaluated by different means of measurement: MFR, DSC, colorimetry, IR-spectroscopy and oxygen absorption. The results indicate that polypropylene and polypropylene with dispersed oxygen scavenger degrade by the impact of extrusion which can be seen by increased MFR and crystallinity and color changes. Furthermore the iron particles did undergo changes regarding color and oxygen scavenging capacity. The absorption capacity at 23 °C was reduced by one third from 39 to 48 mg oxygen per one gram scavenger additive after one extrusion to 26–35 mg oxygen per one gram scavenger additive after 9 and 10 extrusion cycles, respectively. Overall the iron based oxygen scavenger has a lower impact on degradation than the temperature and the number of extrusions.
Keywords: Polypropylene (PP); Iron based oxygen scavenger; Multiple extrusion; Polymer degradation; Active packaging; Recycling;
Photo-oxidation of polymer-like amorphous hydrogenated carbon under visible light illumination by Salmaan Baxamusa; Ted Laurence; Matthew Worthington; Paul Ehrmann (133-138).
Amorphous hydrogenated carbon (a-C:H), a polymer-like network typically synthesized by plasma chemical vapor deposition, has long been known to exhibit optical absorption of visible light (λ > 400 nm). Here, we report that this absorption is accompanied by rapid photo-oxidation (within minutes) that behaves in most respects like classic polymer photo-oxidation with the exception that it occurs under visible light illumination rather than ultraviolet illumination. Lower plasma power during deposition produces a-C:H that is less crosslinked, is less absorptive, has longer photoluminescence lifetimes, and has a slower photo-oxidative degradation than a-C:H deposited at higher plasma power. The optical gap of the material deposited here is ∼2.5 eV, and we correspondingly observe photo-oxidation at photon energies of 2.7 and 3.1 eV. A reduced photo-oxidative response is observed at sub-gap energies, suggesting that defect states or absorption tails enable absorption at lower energies. The photo-oxidation depends on both the total accumulated dose as well as the intensity of the illumination, suggesting either a transport limitation of O2 in the a-C:H or a complex reaction pathway. Under typical laboratory lighting conditions, plasma CVD a-C:H continues to photo-oxidize for more than 20 weeks, demonstrating that any characterization of the long-term behavior of a-C:H under use conditions requires control of not only atmospheric conditions but also ambient lighting environment.
Keywords: Amorphous hydrogenated carbon; Plasma polymer; Photo-oxidation; Visible light; Aging;
Flame resistance and aging mechanism of flame retardant polycarbonate sheet containing linear phenolic resin charring agent by Hao Huang; Yan Shi; Gaopeng Lv; Yuan Liu; Qi Wang (139-145).
The preparation of halogen-free flame retardant thin-wall polycarbonate (PC) sheet with high performance is a global challenge. In our research, a composite flame retardants system composed of polysiloxane and perfluorinated sulfonate combined with a macromolecular charring agent, linear phenolic resin (LPR) could endow PC sheets (thickness: 0.4 mm) with UL94-V0 rating, showing high flame resistance efficiency. Regrettably, this efficient flame retardant system made the aging properties of PC seriously deteriorated due to the transesterification reaction between the phenolic hydroxyls and PC macromolecular chains, thus losing practical applied value. Introducing a small amount of boron acid (HB) could solve the fatal shortcoming through a quick coordination reaction between the boron atom and phenolic hydroxyl to effectively protect the PC backbone chains, and meanwhile further improve the flame retardance by increasing the charring stability of LPR due to the formed B–O bond with higher energy.
Keywords: Polycarbonate sheet; Flame retardance; Linear phenolic resin; Charring agent; Aging properties;
Opposite effects of a singlet oxygen quencher on photochemical degradation of dicyano-substituted poly(phenylenevinylenes) with different side chains by Logan P. Sanow; Cheng Zhang (146-152).
RO-diCN-PPV and C8-diCN-PPV, poly(1,4-phenylene-1,2-dicyanovinylene) with alkoxy and octyl side chains, have recently been shown to photodegrade via a singlet oxygen mechanism, and RO-diCN-PPV is seven times more stable. To improve photostability, 1,4-diazabicyclo[2.2.2]octane (DABCO), a singlet oxygen quencher, was used as a dopant. To our surprise, DABCO exhibited opposite effects on their photodegradation. With 15 mol% DABCO, degradation rate of C8-diCN-PPV decreased by 65%, while that of RO-diCN-PPV increased by 246%. The DABCO content in C8-diCN-PPV film remained unchanged during 20 min of illumination, but mostly disappeared in RO-diCN-PPV in only 5 min due to decomposition. IR and MW analysis results suggest that DABCO slowed down degradation of C8-diCN-PPV without altering the mechanism, but accelerated RO-diCN-PPV photodegradation by initiating a radical process. C8-diCN-PPV's HOMO energy is lower than that of DABCO by 1.78 eV, a gap too wide for efficient electron transfer to happen. On the other hand, the HOMO of RO-diCN-PPV is only lower by 1.14 eV, allowing DABCO to donate electron to photoexcited RO-diCN-PPV to initiate a radical process that damaged the polymer and destroyed DABCO itself. It was also found that, in RO-diCN-PPV, radical decomposition takes very different paths from those of RO-PPVs and produce very different products.RO-diCN-PPV and C8-diCN-PPV photodegrade via singlet oxygen mechanism and RO-diCN-PPV is seven times more stable. 1,4-diazabicyclo[2.2.2]octane (DABCO), a well-known singlet oxygen quencher, exhibits opposite effects on photodegradation of the polymers. With 15 mol% DABCO, degradation rate of C8-diCN-PPV decreased by 65%, while that of RO-diCN-PPV increased by 246%. Electron donation from DABCO to RO-diCN-PPV can happen upon photoexcitation and results in generation of DABCO cationic radicals which initiate a radical process that damages the polymer and destroys DABCO.Display Omitted
Keywords: Photodegradation; Photostability; Dicyano poly(phenylenevinylene); Singlet oxygen; Superoxide radical; DABCO;
Studies on the morphology, properties and biocompatibility of aliphatic diisocyanate-polycarbonate polyurethanes by Borja Fernández-d’Arlas; Ana Alonso-Varona; Teodoro Palomares; M Angeles Corcuera; Arantxa Eceiza (153-160).
Here it is addressed the results on the preparation of a novel set of biocompatible thermoplastic polyurethane (PU) elastomers. The main purpose of this work was to study the nano/microstructure obtained when substituting commonly used aromatic diisocyanates, such as 4,4′-methylene diphenyl diisocyanate (MDI) by the more biocompatible and also more crystalline aliphatic 1,6-hexamethylene diisocyanate (HDI). The work aims to relate its physico-chemical characteristics with macroscopic properties such as hydrophobicity, thermal characteristics, mechanical properties, biodegradability and biocompatibility. Substitution of MDI by HDI developed more phase segregated materials with higher surface tension, allowing minimization of diisocyanate content into the PU for achieving the optimal biocompatible range. The polycarbonate blocks provide biostability over a period of 2 years. In addition, these materials were not cytotoxic and revealed good adhesion of the cells, assessed by SEM, suggesting that they may be valid candidates for biomedical use.
Keywords: Hexamethylene diisocyanate; Aliphatic polyurethane; Polycarbonate; Morphology; Properties; Hydrolitic stability;
Synthesis and characterization of cyclic bisphenol A (phenylene phosphonate) oligomer and its flame retardancy application by Nana Li; Guowei Jiang; Guangyuan Zhou (161-168).
A novel solid flame retardant cyclic bisphenol A (phenylene phosphonate) (CPBA) oligomer was synthesized in high yields by the reaction of phenylphosphonic dichloride with bisphenol A under pseudo-high-dilution conditions via polycondensation. Detailed structural characterizations of this oligomer were conducted using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, 1H NMR, 31P NMR and FTIR. Furthermore, the flame-retardant efficiency of this oligomer in polybutylene terephthalate (PBT) was investigated using limiting oxygen index (LOI) and UL-94 tests. After the addition of 25 wt.% CPBA, the LOI increased from 20.2% to 28.6% and the UL-94 V-0 rating was achieved. Thermogravimetric analysis, FTIR, and Pyrolysis/GC/MS were employed to elucidate the pyrolysis behavior of CPPA and PBT/CPBA. Results showed that the CPBA oligomer could change the degradation path of PBT and improved the char formation of the PBT/CPBA systems. The residual morphologies of residues of the PBT/CPBA25% system were investigated by scanning electron microscopy (SEM). SEM investigations revealed that the residual chars containing polyphosphoric or phosphoric acid, which plays an important role in the process of carbonization. The influence of CPBA content on the mechanical properties of PBT/CPBA blends was also discussed.
Keywords: Cyclic bisphenol A (phenylene phosphonate); Polybutylene terephthalate; TGA; Flame retardancy; FTIR; Pyrolysis/GC/MS;
Degradation of γ-irradiated polyethylene-ethylene vinyl alcohol-polyethylene multilayer films: An ESR study by Gérard Audran; Samuel Dorey; Nathalie Dupuy; Fanny Gaston; Sylvain R.A. Marque (169-179).
The present work aims to investigate by ESR the effects of γ-irradiation on antioxidants and on solid multilayer films used in biomedical applications. The multilayer films analyzed here are mainly composed of polyethylene and ethylene vinyl alcohol. Radical species are monitored over time after γ-irradiation at several doses (30, 50, 115 and 270 kGy) using ESR to assess the impact of the dose-value on the formation of the radicals.
Keywords: Electron spin resonance investigation; γ-irradiation; Polyethylene; Ethylene vinyl alcohol; Antioxidants; Additives;
Weathering of a polyester-urethane clearcoat: Lateral inhomogeneities by Hesam Makki; Koen N.S. Adema; Marco M.R.M. Hendrix; Elias A.J.F. Peters; Jozua Laven; Leendert G.J. van der Ven; Rolf A.T.M. van Benthem; Gijsbertus de With (180-186).
This paper is devoted to the surface analysis of a polyester-urethane coating during weathering under different conditions using artificial weathering machines. By means of atomic force microscopy (AFM), the evolution of the surface topology of the coatings is studied. Degradation is shown to be a laterally inhomogeneous process. The presence of water facilitates material removal and leads to an increase in the surface roughness and consequently a gloss loss. In addition, by comparing degradation under aerobic and anaerobic conditions, it is shown that oxidation reactions are the main cause of lateral inhomogeneous degradation of coatings.
Keywords: Polyester-urethane; Surface topology; Weathering; AFM;