Polymer Degradation and Stability (v.96, #9)
Obituary: Jan Pospíšil (10. 5. 1926–15. 4. 2011) by Jan Pilař (1537).
Flame retardation of glass-fibre-reinforced polyamide 6 by a novel metal salt of alkylphosphinic acid by Zhi Hu; Li Chen; Gong-Peng Lin; Yuan Luo; Yu-Zhong Wang (1538-1545).
Aluminum salts of phosphinic acid mixture of diisobutylphosphinic acid and monoisobutylphosphinic acid (HPA-2TBA-Al) and glass fibres were compounded with polyamide 6 to prepare a series of flame retardant GF/PA6 composites via melt blending. The flame retardance and burning behaviors of the composites were investigated by limiting oxygen index (LOI), vertical burning test (UL-94), and Cone calorimeter test. The thermal properties and decomposition kinetics were investigated by thermogravimetric analysis (TGA) under N2 atmosphere. Addition of HPA-2TBA-Al results in an increased LOI value, a UL-94 V-0 rating together with a decrease in both the values of PHRR and THR in Cone calorimetric analysis. Visual observations and scanning electronic microscopy (SEM) after flame retardant tests confirmed the char-formation which acts as a fire barrier in condense phase. Analysis of cone calorimeter data indicates that gas phase flame retardant mechanism exists in the GFPA6/HPA-2TBA-Al system.
Keywords: Polyamide 6; Glass fibre; Alkylphosphinate; Flame retardance;
Effect of thermal history on the mechanical properties of three polypropylene impact-copolymers by J. Jancar; J. Tochacek (1546-1556).
The effect of thermal history on static mechanical properties and impact fracture behavior of three reactor polypropylene impact-copolymers (ICPPs) was investigated for three ICPPs prepared using commercial Innovene®, Unipol® and Spheripol® polymerization technologies. Multiple extrusion employing a co-rotating twin-screw extruder resulted in a significant reduction of the molecular weight of the PP homopolymer phase evidenced by the increasing melt flow index (MFI). Neither cross-linking of the ethylene-propylene rubber (EPR) phase nor EPR particle coarsening was detected for any of the ICPPs after 5 consecutive extrusions. Decreasing molecular weight of the PP homopolymer phase caused change in the crystalline morphology of injection molded specimens due to the change in crystallization kinetics and reduction of the number of tie molecules, however, the overall degree of crystallinity did not change, significantly. The static tensile mechanical properties (E, σy, ɛb), critical strain energy release rate, G c, and the Charpy notched impact strength, a k, decreased with increasing MFI in a monotonous manner for all the ICPPs investigated. Despite significant differences between the absolute values of the mechanical properties for the three ICPPs, the MFI dependence of the σy and G c relative to that for the unaffected ICPP fell on a single master curve for all of them. High-speed digital camera, used to follow the fracture process during the instrumented impact test, revealed no significant change of the small scale yielding fracture process with increasing MFI. This was in an agreement with the negligible change in the size of the crack tip plastic zone, R p, predicted using simple mixed mode fracture model. The plane strain value of the critical strain energy release rate, G1c, calculated from the measured G c for the INN (2.4 kJ/m2), UNI (2.8 kJ/m2) and SPH (3.5 kJ/m2) using a simple LEFM model did not exhibit significant dependence on the number of extruder passes. The observed differences between the three ICPPs were ascribed to the significantly larger EPR content in UNI compared to the other two ICPPs and significantly larger content of isotactic PP homopolymer in the INN compared to the remaining two ICPPs.
Keywords: Impact-copolymer; Polypropylene; Multiple extrusion; Mechanical properties; Morphology;
Effect of a phosphorus-containing flame retardant on the thermal properties and ease of ignition of poly(lactic acid) by Lian-Lian Wei; De-Yi Wang; Hong-Bing Chen; Li Chen; Xiu-Li Wang; Yu-Zhong Wang (1557-1561).
An aryl polyphenylphosphonate, poly(9-oxa-10-(2,5-dihydro-xyphenyl) phospha-phenanthrene-10-oxide) phenylphosphonate (WLA-3), was used to prepare a flame-retardant poly(lactic acid) (PLA) by direct melt compounding. The thermal behaviour, burning behaviour and mechanical properties of the flame-retardant PLA systems have been investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), vertical burning test (UL-94), limiting oxygen index (LOI), cone calorimeter test (CCT) and tensile test. The flame retardance mechanism has been studied via Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and P content analysis. The UL-94 ratings of PLA’s containing 7phr (W7P) and 10phr (W10P) of WLA-3 were enhanced to V-0 from no rating for neat PLA. However, the cone calorimetry of flame-retardant PLA (W7P) only showed a little decrease in heat release rate (HRR), peak of heat release rate (PHRR) and total heat release (THR) compared to neat PLA. TGA results showed that the PLA containing different amounts of WLA-3 presented more complicated thermal decomposition behaviours than neat PLA. Additionally, the results from DSC and tensile tests showed that the addition of WLA-3 into PLA had a slight impact on the crystallization behaviours and tensile properties.
Keywords: Poly(lactic acid); Flame retardant; Phosphorus; Burning behaviour;
Calcium and aluminium-based fillers as flame-retardant additives in silicone matrices II. Analyses on composite residues from an industrial-based pyrolysis test by Siska Hamdani-Devarennes; Audrey Pommier; Claire Longuet; José-Marie Lopez-Cuesta; François Ganachaud (1562-1572).
The second part of this series, devoted to the study of model fire-resistant silicone composites filled with calcium or aluminium-based material which would meet cable industry specifications, focuses on residues obtained after extreme pyrolysis adapted from the NFC 32070 CR1 French standard. Several methods of analysis (among them ESEM, EDX, XRD, Hg pycnometer, and compression tests) have been carried out in order to investigate the microstructure, volume variation, and compression behaviour of silicone composite residues. Calcium-based fillers produced more cohesive residues than aluminium-based fillers. Indeed, the co-crystallisation taking place during pyrolysis, as shown in the first part of this series (Hamdani, S. et al., Polym Degrad Stab, 2010, 95, 1911–1919), produced a dense and strong residue. The strong internal porosity and absence of new crystal formation in residues of aluminium-based filled composites resulted in their low compressive resistance. In addition, water release during the degradation of the latter fillers, favoured residue expansion, high interior porosity and thus weak compression resistance.
Keywords: Silicone; Fillers; Calcium; Aluminum; Pyrolysis; Residue;
Non-isothermal thermogravimetry, differential scanning calorimetry and chemiluminescence in degradation of polyethylene, polypropylene, polystyrene and poly(methyl methacrylate) by Jozef Rychlý; Lyda Matisová-Rychlá; Katarína Csomorová; Ivica Janigová; Michael Schilling; Tom Learner (1573-1581).
The degradation of pure polymers such as polyethylene, polypropylene, polystyrene and poly(methyl methacrylate) in nitrogen and oxygen was characterized by means of non-isothermal thermogravimetry, chemiluminescence and differential scanning calorimetry. The link between the results of the different methods based on Bolland Gee scheme of polymer oxidation is described. From the set of parameters determined from the thermogravimetry, the rate constants based upon the sum of several temperature dependent first-order processes were calculated and compared with those obtained by an iso-conversional method derived for several heating rates. Competition between propagation of oxidation and depolymerisation to monomer is proposed to explain the differences in kinetic behaviour of the examined polymers.
Keywords: Non-isothermal thermogravimetry; Chemiluminescence; DSC; Rate constants;
Influence of steam explosion on the thermal stability of cellulose fibres by N. Jacquet; N. Quiévy; C. Vanderghem; S. Janas; C. Blecker; B. Wathelet; J. Devaux; M. Paquot (1582-1588).
The aim of the present study was to compare the effect of different steam explosion treatments on the thermal degradation of a bleached cellulose. The intensity of a steam explosion treatment, which allows breakdown of the structural lignocellulosic material was determined by a correlation between time and temperature of the process.Results of this study showed that thermal degradation of cellulose fibres was limited when the severity factor applied was below 4.0. For higher intensities, determination of the degradation products in the water-soluble extract showed an important increase of the 5-hydroxymethyl-furfural concentration with the temperature. When the severity factor reached 5.2., TGA analysis showed that the increase of degradation products was coupled to an increase of the char level meaning a strong degradation of the cellulose. dTGA behaviour also showed that thermal stability of the steam explosion samples decreased with the intensity of the treatment. To conclude, a theoretical diagram predicting the degradation of the cellulose during the steam explosion treatment was established.
Keywords: Steam explosion; Microcrystalline cellulose; Degradation mechanism; Hydroxymethyl-furfural;
Hydrolytic degradation of poly(d,l-lactide-co-glycolide 50/50)-di-acrylate network as studied by liquid chromatography–mass spectrometry by Ron Peters; Jeromme Lebouille; Bart Plum; Peter Schoenmakers; Sjoerd van der Wal (1589-1601).
The soluble products of the hydrolytic degradation of photochemically cross-linked poly-(d,l-lactide-co-glycolide 50/50)-di-acrylate film were analysed at different stages to obtain insight into the complex (bio)degradation processes. Liquid chromatography–mass spectrometry analyses have been used to identify and quantify the various oligomeric and polymeric degradation products from the soluble fraction. The products were analysed directly after release and also after complete hydrolysis of the soluble fraction. The study shows a rapid release of residual photo-initiator followed by a gradual release of lactide/di-ethyleneglycol/glycolide oligomers with varying composition and chain length. The final stage of the sigmoidal weight loss profile reflects the release of polyacrylate chains with lactide/glycolide side chains. The molecular weights of the polyacrylate chains released increase with degradation time, which indicates that the release of these polyacrylate chains is determined by the number and type of ester-groups that must be degraded hydrolytically to dissolve these chains. The analysis of the soluble degradation products provides detailed insights in the chemical changes at the different stages of degradation; extraction, network attack, network penetration, bulk degradation, and finally release of persistent network fragments. Chromatographic and mass spectrometric techniques prove to be powerful tools to enhance the understanding of the hydrolytic degradation of chemically cross-linked acrylates.
Keywords: Lactide; Degradable polymer networks; Photopolymerisation; Characterisation; Degradation; LC-MS;
Crystallization behavior, thermal property and biodegradation of poly(3-hydroxybutyrate)/poly(ethylene glycol) grafting copolymer by Cai Zhijiang; Hou Chengwei; Yang Guang (1602-1609).
The poly(3-hydroxybutyrate)(PHB)/poly(ethylene glycol)(PEG) grafting copolymer was successfully prepared by PHB and acrylate groups ended PEGM using AIBN as initiator. The crystallization behavior, thermal stability and environmental biodegradability of PHB/PEG grafting copolymers were investigated with differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and Biodegradation test in vitro. In the results, all the grafting copolymers were found to show the X-ray diffraction arising from the PHB crystal lattice, while none of the PEG crystallized peaks could be found even though the graft percent reached 20%. This result indicated that PEG molecules were randomly grafted onto PHB chain. The thermal properties measured by DSC showed that the melting temperature(T m) and glass transition temperature (T g) were both shifted to lower temperature with the graft percent increasing, and this broadened the narrow processability window of PHB. According to TGA results, the thermal stability of the grafting copolymers is not changed compared to pure PHB. From the biodegradation test, it could be concluded that degradation occurred gradually from the surface to the inside and that the degradation rate could be adjusted by the PEG grafting ratio. In another words, the biodegradation profiles of PHB/PEG grafting copolymer can be controlled. These properties make PHB/PEG grafting copolymer have promising potential applications especially in agriculture fields.
Keywords: Poly(3-hydroxybutyrate); Polyethylene glycol; Grafting reaction; Crystallization behavior; Enzymatic biodegradation;
Thermal stability of polybenzoxazines with lanthanum chloride and their crosslinked structures by Qi-Chao Ran; Nian Gao; Yi Gu (1610-1615).
Lanthanum chloride (LaCl3) was incorporated into five kinds of benzoxazines by different preparation methods. The thermal stability and the structures of polybenzoxazines were characterized by thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The evolved gases from the degradation process of polybenzoxazines were analyzed by FTIR. The results showed that the thermal stability and char yields of three kinds of polybenzoxazines containing LaCl3 can be improved obviously. LaCl3 has an important effect on the polymerization reactions of benzoxazines. More stable arylamine Mannich bridges were observed in the chemical structures of the polybenzoxazines. It is these structures that can effectively retard the volatilization of aniline derivatives and result in the improvement of the thermal stability of the polybenzoxazines.
Keywords: Thermal stability; Polybenzoxazines; Lanthanum chloride; Arylamine Mannich bridges; TGA–FTIR;
The absence of size-dependency in flame retarded composites containing low-melting organic–inorganic glass and clay: Comparison between micro- and nanocomposites by Dan Yu; Malte Kleemeier; Guang Mei Wu; Bernhard Schartel; Wei Qu Liu; Andreas Hartwig (1616-1624).
Due to optimised processing of epoxy based composite materials containing a low-melting organic–inorganic glass together with an organo clay, the size of the glass particles could be successfully reduced. Thus truly nano-dispersed composites were obtained, with glass particles in the range of 10 nm to 200 nm. The small particle size allowed efficient interaction of glass particles and organo clay layers. The flame retardancy as well as the thermo-mechanical properties were tested, and the results showed that the low-melting glass led to a remarkable reduction of peak heat release rate by forming an enhanced barrier layer. Nevertheless no further improvement could be achieved by lowering the particle size to the nanometre region. For good flame retardancy a microdispersion of the low-melting glass was already sufficient.
Keywords: Epoxy resin; Nanocomposites; Low-melting glass; Clay; Flame retardancy;
Stability of a salicylate-based poly(anhydride-ester) to electron beam and gamma radiation by Roselin Rosario-Meléndez; Linda Lavelle; Stanko Bodnar; Frederick Halperin; Ike Harper; Jeremy Griffin; Kathryn E. Uhrich (1625-1630).
The effect of electron beam and gamma radiation on the physicochemical properties of a salicylate-based poly(anhydride-ester) was studied by exposing polymers to 0 (control), 25 and 50 kGy. After radiation exposure, salicylic acid release in vitro was monitored to assess any changes in drug release profiles. Molecular weight, glass transition temperature and decomposition temperature were evaluated for polymer chain scission and/or crosslinking as well as changes in thermal properties. Proton nuclear magnetic resonance and infrared spectroscopies were also used to determine polymer degradation and/or chain scission. In vitro cell studies were performed to identify cytocompatibility following radiation exposure. These studies demonstrate that the physicochemical properties of the polymer are not substantially affected by exposure to electron beam and gamma radiation.
Keywords: Polyanhydride; Sterilization; Drug release; Gamma irradiation; Electron beam; Stability;
Influence of cellulose nanowhiskers on the hydrolytic degradation behavior of poly(d,l-lactide) by Everton Luiz de Paula; Valdir Mano; Fabiano Vargas Pereira (1631-1638).
This paper reports the preparation of bionanocomposites based on poly(d,l-lactide) and cellulose nanowhiskers (PDLLA/CNWs) and studies the influence of the CNWs on the hydrolytic degradation behavior of the polylactide. The hydrolytic degradation process was studied in a phosphate buffer medium through the sample weight loss and also by FTIR, DSC and TGA measurements. The presence of CNWs induced a strong delay in the hydrolytic degradation of the PDLLA, even when the concentration of the nanofillers was only 1%. This effect was related to the physical barrier created by the highly crystalline CNWs that inhibited water absorption and hence retarded the hydrolytic degradation of the bionanocomposites. In addition, the incorporation of cellulose nanocrystals in the PDLLA also made the biopolymer more thermally stable, increasing the initial temperature of mass loss even after the degradation in phosphate medium. The results presented here show the possibility of controlling the biodegradability and prolonging the service life of a polylactide through the incorporation of a small quantity of nanofillers obtained from renewable materials.
Keywords: Hydrolytic degradation; Cellulose nanowhiskers; Poly(d,l-Lactide); Bionanocomposite;
Poly(ɛ-caprolactone)-based ‘green’ plasticizers for poly(vinyl choride) by Guixin Shi; David G. Cooper; Milan Maric (1639-1647).
A series of proposed plasticizers for poly(vinyl chloride) (PVC), based on poly(ɛ-caprolactone) (PCL) with octanoate and benzoate-terminal groups, were synthesized with various microstructures and molecular weights (MW) and tested for biodegradability as well as for mechanical performance, and leaching resistance in blends with PVC. The plasticization efficiency of each was characterized by measuring the glass transition temperature (T g) and tensile properties of PCL/PVC blends. The PCL-octanoate plasticizers demonstrated plasticization efficiency similar to di(ethylhexyl) phthalate (DEHP) with the same plasticizer loading. PCL-benzoate/PVC blends had much higher T gs (∼20 °C higher) compared to PCL-octanoate/PVC and DEHP/PVC blends. Yield stresses were about two times higher for PCL-benzoate/PVC blends compared to PCL-octanoate/PVC and DEHP/PVC blends, reflecting the stiffer nature of such blends. Biodegradation was rapid for all PCL-octanoates, with the exception of linear PCL-octanoates with arm molecular weights >103 g mol−1. Biodegradation rates of PCLs by Rhodococcus rhodocrous were not affected by microstructure for the range of PCL topologies studied (linear versus three or four arms) but were slower for PCLs made from commercial PCL-diols that had a central ether linkage due to the initiator used to make these compounds. Leaching resistance was higher as PCL molecular weight increased and, for pairs of comparable sized species, significantly less PCL-benzoate leached out compared to the PCL-octanoate. For the range of PCL topologies studied, the number of arms did not significantly affect leaching resistance. In summary, both the end group and the molecular weight influenced the leaching resistance of the PCL. PCL-octanoates were comparable plasticizers to DEHP in terms of the mechanical properties examined, and were rapidly degraded by a common soil microorganism.
Keywords: Poly(ɛ-caprolactone); ‘Green’ plasticizer; Biodegradation; DEHP; PVC;
Interactions between polypropylene and photochromic dyestuffs by Axel Nechwatal; Monika Nicolai (1648-1652).
Polypropylene that contains photochromic dyestuffs ages faster than pure polypropylene. This influence strongly depends on the dyestuff type. Chemiluminescence measurements can be used as an indicator for the ageing of polypropylene and for researching the photochromic degradation.
Keywords: Photochromism; Polypropylene; Photochromical fatigue; Chemiluminescene; Naphthoxazine; Naphthopyrane;
Thermal and microbial degradation of alginate-based superabsorbent polymer by Ying-Ning Phang; Swee-Yong Chee; Chee-Onn Lee; Yok-Lan Teh (1653-1661).
In this study, an alginate-based superabsorbent polymer (SAP), alginate-graft-poly[acrylamide-co-(itaconic acid)-g-(acrylic acid)] or Alg-g-P(AM-co-IA-g-AA), was prepared to examine its thermal and microbial degradation properties through Thermogravimetric Analysis (TGA), and soil supernatant test (with and without added nutrient) and soil burial test, respectively. The TGA thermogram of the SAP showed three degradation steps. The first degradation step was due to the thermal degradation of alginate and decomposition of the functional groups of PAM, PIA and PAA; whereas the second degradation step occurred as a result of the decomposition of PAM, PAA and PIA chains. Further decomposition of PIA contributed to the third degradation step. Among all the soil samples [tropical forest soil (TF), former tin mine lake soil (TM), peanut farm soil (PF), indigenous microorganism soil from an organic vegetable farm (OF), and oil palm plantation soil (OP)] tested, OF soil degraded the polymer sample most effectively, with the highest weight loss of 82.6% (with added nutrient) and 82.8% (without added nutrient) in soil supernatant tests, and 63.5% in soil burial test. Morphological observation under an Illuminated Stereo Microscope showed some holes and weak topographical spots on the surface of the polymer material after it had been incubated in OF solution for 40 days. Meanwhile, the intrinsic viscosities, [η], of NaAlg and the Alg-based SAP solutions were 2.62 and 2.75 respectively.
Keywords: Biodegradability; Soil burial test; Superabsorbent polymer; Thermal degradation;
Microbial desulfurization of ground tire rubber by Thiobacillus ferrooxidans by Yuanhu Li; Suhe Zhao; Yaqin Wang (1662-1668).
This study focused on the microbial desulfurization of ground tire rubber (GTR) by Thiobacillus ferrooxidans, which selected from the soil of an iron mine had strong sulphur oxidizing capacity. GTR was desulfurizated in the modified Silverman medium during the cultivation of T. ferrooxidans for 30 days, and T. ferrooxidans was able to maintain a high biomass. The continuous increase of SO4 2− in the medium indicated that the sulfur on the surface of GTR was oxidized. FTIR-ATR and XPS spectra revealed that a rupture of conjugated C＝C bonds and a reduction of sulfur content on the surface of GTR had occurred during desulfurization. The sol fraction of GTR increased from its original 4.69%–7.43%. Compared with GTR sheet, desulfurizated GTR (DGTR) sheets had much smoother surfaces, better physical properties, and higher swelling values. NR vulcanizates filled with DGTR (with 10–40 phr loading) had lower crosslink density and better mechanical properties than those filled with GTR at the same loading. The results determined by DMA suggested that NR vulcanizates filled with DGTR had a reduction of molecular chain friction resistance during glass transition and SEM photograph indicated a better interface coherence between DGTR and NR matrix.
Keywords: Ground tire rubber; Microbial desulfurization; Thiobacillus ferrooxidans; Crosslink density; Mechanical properties;
Inherent flame retardation of bio-based poly(lactic acid) by incorporating phosphorus linked pendent group into the backbone by Xiao-Ya Yuan; De-Yi Wang; Li Chen; Xiu-Li Wang; Yu-Zhong Wang (1669-1675).
The molecular design for inherently flame-retardant poly(lactic acid) (IFR-PLA) was outlined and achieved by chemically incorporating an effective organophophorus-type flame retardant (FR) into the PLA backbone via the chain extension of the dihydroxyl-terminated prepolymer with 1, 6-hexamethylene diisocyanate (HDI). The structure of IFR-PLA was characterized by 1H- and 31P-nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. IFR-PLA was further blended with the commercial PLA to prepare flame retardant PLA blends (PLA-FR blend). The relevant properties of IFR-PLA and PLA-FR blends were evaluated by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), limiting oxygen index (LOI) measurements and UL-94 tests. The thermal analysis revealed that the char yield of IFR-PLA and PLA-FR blend above 400 °C was greatly enhanced compared to that of pure PLA. The LOI value was significantly improved from 19 for pure PLA to 29 when 1 wt% of phosphorus content was introduced and all IFR-PLA samples achieved V-0 rating in the UL-94 tests. PLA-FR blends had an LOI value of 25–26 and UL-94 V-2 rating at 20 wt% of IFR-PLA content. The tensile strength of all the FR PLA systems was ca. 60 MPa. The method used in this study provided a novel route to permanently flame retard PLA.
Keywords: Flame retardance; Poly(lactic acid); Chain-extension; Phosphorus;
Free volume related fluorescent behavior in electron beam irradiated chalcone doped PVA by V. Ravindrachary; Ismayil; Suresh P. Nayak; Dhanadeep Dutta; P.K. Pujari (1676-1686).
Effect of electron irradiation on the free volume related microstructural and optical properties of chalcone doped Poly(vinyl alcohol) composite films have been studied using FTIR, UV–Visible, XRD and Positron Annihilation techniques. The FTIR spectral study shows that the irradiation induces the crosslinking within the composite. Using UV–Visible absorption spectra the optical energy band gap and activation energies were estimated and the variation of these parameters suggests the existence of defects and molecular ordering within the irradiated composite. XRD diffractograms reveal that the crosslinking enhances the crystallinity of the sample. In this cross-linked polymer composite the fluorescence enhancement has been observed in the fluorescence spectral study. The Positron annihilation result suggests that the irradiation affects the free volume properties and crosslinking hinders the chalcone chromophore molecular rotation. Under this restricted condition the chromophore molecules likely to emit enhanced fluorescence and its mobility is directly related to the free volume around it.► Electron irradiation effect on the chalcone doped PVA composite films are studied. ► Optical study shows the irradiation produces defects and molecular ordering. ► XRD diffractograms reveal that the crosslinking enhances the crystallinity. ► PALS suggests the modifications in free volume and chromophore rotational hindrance. ► Enhanced fluorescence by chromophore depends on its hindrance and free volume.
Keywords: Poly(vinyl alcohol) (PVA); Electron irradiation; Free volume; Crosslinking; Fluorescence;
Degradation studies on segmented polyurethanes prepared with poly (d, l-lactic acid) diol, hexamethylene diisocyanate and different chain extenders by Yuanliang Wang; Changshun Ruan; Jiaoxia Sun; Maolan Zhang; Yanglan Wu; Kun Peng (1687-1694).
In order to investigate the effect of different chain extenders on degradation properties of segmented polyurethanes (SPUs), three types of segmented polyurethanes (SPU-P, SPU-O and SPU-A) based on poly (d, l-lactic acid) diol, hexamethylene diisocyanate (HDI), were synthesized with three chain extenders: peperazine (PP), 1, 4-butanediol (BDO) and 1, 4-butanediamine (BDA), respectively. Thermogravimetric analysis, activation energy and in vitro degradation were used to characterize the obtained polymers, quantitatively. The results revealed that chain extender played an important role in thermal degradation and biodegradation of polyurethanes. Thermogravimetric analysis and activation energy demonstrated that SPU-O, SPU-P and SPU-A presented best, second and weakest thermostability, respectively, and the thermal degradation mechanism of three SPUs was the same and regarded as a two-stage degradation. Data of hydrolytic degradation of the polymers during 12 weeks indicated that the in vitro degradation stability of SPU-A and SPU-P was similar, but both were better than that of SPU-O. The reason for the differences among three types of SPUs was discussed in this paper.
Keywords: Segmented polyurethane; Chain extender; Thermal degradation; In vitro degradation;
Synthesis, characterization, degradation of biodegradable castor oil based polyesters by P.S. Sathiskumar; Giridhar Madras (1695-1704).
A new family of castor oil based biodegradable polyesters was synthesized by catalyst free melt condensation reaction between two different diacids and castor oil with d-mannitol. The polymers synthesized were characterized by NMR spectroscopy, FT-IR and the thermal properties were analysed by DSC. The results of DSC show that the polymer is rubbery in physiological conditions. The contact angle measurement and hydration test results indicate that the surface of the polymer is hydrophilic. The mechanical properties, evaluated in the tensile mode, shows that the polymer has characteristics of a soft material. In vitro degradation of polymer in PBS solution carried out at physiological conditions indicates that the degradation goes to completion within 21 days and it was also found that the rate of degradation can be tuned by varying the curing conditions.
Keywords: Castor oil; Aliphatic polyesters; Soft thermoset; Biodegradable polymer;
Chain cleavage mechanism of palm kernel oil derived medium-chain-length poly(3-hydroxyalkanoates) during high temperature decomposition by Mei Chan Sin; Seng Neon Gan; Mohd Suffian Mohd Annuar; Irene Kit Ping Tan (1705-1710).
Medium-chain-length poly(3-hydoxyalkanoates) (mcl-PHAs) are natural polyesters having the molecular formula of [∼OCHR–CH2–COO∼]n, composed of monomers each having 6 to 14 carbon atoms, with relatively bulky alkyl pendant group. They are primarily synthesized by fluorescent pseudomonads under unbalanced nutrient availability as carbon and energy storage compounds. From thermogravimetic analysis, the mcl-PHAs produced from Pseudomonas putida grown on palm kernel oil showed a drastic decomposition at temperature above 195 °C. An increase of HO–CHR∼∼ terminals was observed when the mcl-PHAs were thermally decomposed at 160–180 °C, which was presumably due to the hydrolytic chain cleavage initiated at –COO–CHR∼∼, the main skeletal bonds of the biopolyester. At 190 °C, molecules with RCH≡CH∼∼ were also observed as minor decomposition products from the FTIR and NMR measurements and this could be probably due to the dehydration of HO–CHR∼ groups of hydroxyl acids, producing terminally unsaturated oligomers. These observations were consistent with the detection of three new unsaturated monomers: C4:1, C6:1 and C8:1 in the methanolyzed mcl-PHAs in gas chromatography analysis.
Keywords: Chain cleavage mechanism; Mcl-PHA; Palm kernel oil; FTIR; NMR; GC;