Polymer Degradation and Stability (v.98, #5)

In this study novel flame retardant boron phosphate (BPO4)/polyimide composites were prepared. 4,4′-Oxydianiline (ODA) was reacted with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) in dimethyl formamide (DMF) and mixed with BPO4 particles to obtain a series of polyamic acids, meanwhile, corresponding polyimides were synthesized via the thermal imidization technique. The amount of BPO4 in the composite films was varied from 0 wt% to 10 wt%. The structure, thermal and surface properties of the polyimide films were characterized by means of ATR-FTIR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The flame retardancy of the composite materials was examined by limiting oxygen index (LOI) measurements and UL-94 VTM tests. Result showed that the LOI values of composites increased from 28 to 39. Furthermore, proton conductivity of polyimide films was measured by the four probe technique. The composite membrane containing 3 wt% of BPO4 showed a conductivity of 0.4 mS/cm at room temperature.
Keywords: Boron phosphate; Flame retardant; Proton conductivity; Polyimide; Composite; Mechanical properties;

Enzymatic hydrolysis studies on novel eco-friendly aliphatic thiocopolyesters by Matteo Gigli; Andrea Negroni; Michelina Soccio; Giulio Zanaroli; Nadia Lotti; Fabio Fava; Andrea Munari (934-942).
Copolymers of poly(butylene succinate) (PBS) containing thiodiethylene succinate sequences with different molecular architectures (PBSPTDGS) were prepared via reactive blending in the presence of a Ti-based catalyst. In particular, a block copolymer with long sequences and a random one have been investigated for their biodegradability. The parent homopolymer PBS has been also synthesized via the usual two-stage melt polycondensation and used as reference polymer in the study.The hydrolitic treatment carried out using lipase from Candida cylindracea ([E] = 50 U/ml, T = 30 °C and pH = 7.0), showed that copolymers biodegraded more rapidly and extensively than PBS.ATRIR analysis and DSC measurements also performed on the resulting samples showed that the enzyme simultaneously attacks the amorphous phase and the PTDGS crystalline phase, which is characterized by lower packing density and degree of perfection with respect to the PBS one. This result suggested that the higher degradability of the copolymers under study can be correlated both to the crystallinity degree and to the nature of the crystalline phase. NMR analysis, performed to detect changes in composition of the copolymers during the degradation, demonstrated that enzyme hydrolysis preferentially targeted ester groups of TDGS sequences because of their higher hydrophilicity.
Keywords: Poly(butylene succinate); Copolymers; Thiodiethylene glycol; Solid-state properties; Enzymatic hydrolysis;

Effect of NR on the hydrolytic degradation of PLA by Yun Huang; Chunmei Zhang; Yonghao Pan; Yuli Zhou; Long Jiang; Yi Dan (943-950).
The hydrolytic degradation of PLA and PLA/NR blends in deionized water at 58 °C was studied to reveal the effect of NR on the hydrolysis of PLA. The contact angle and water absorption, the evolution of average molecular weight, mass, morphology and thermal property were investigated. Results show that NR can enhance the hydrophobility of the surface of PLA but it does not cause a decrease of water absorption in the bulk of PLA. On the contrary, the water absorption increases with increasing NR content. The hydrolysis occurs in entire bulk of the specimens not confined in the surface, exhibiting bulk erosion degradation mechanism. NR has no observable effect on the hydrolysis of PLA, which would be beneficial for the biodegradation of PLA toughened by NR. In addition, through the investigation of thermal property, NR has been found to show a hindering effect on the PLA crystalline.
Keywords: PLA; NR; Blend; Hydrolysis; Degradation;

New amphiphilic azo aromatic β-cyclodextrin poly(ether urethanes) with different soft segment lengths have been synthesized and characterized. The thermal stability and kinetic parameters of the synthesized polyurethanes by using thermogravimetry (TG) and derivative thermogravimetry (DTG) under dynamic conditions of temperature, were evaluated. The non-isothermal kinetic parameters of the thermal degradation (activation energy, order of reaction, pre-exponential factor) were discussed in terms of the integral methods: Coats–Redfern, Flynn–Wall, van Krevelen and Urbanovici–Segal. The Reich–Levi method was also employed in evaluation of variation of the kinetic parameters with conversion. Surface parameters were evaluated based on contact angle determinations. Surface-free energy values and the polar and dispersive components were obtained by applying the Owens–Wendt–Rabel and the Kaelbe methods.
Keywords: Poly(ether urethanes); β-Cyclodextrin; Azo chromophore; Thermogravimetry; Surface properties;

Polyethylene glycol-solvolyzed poly-(l)-lactic acids and their stereocomplexes with poly-(d)-lactic acid by Hisanori Ando; Maki Oshima; Yasuhide Nakayama; Atsuyoshi Nakayama (958-962).
Poly-(l)-lactic acid (PLLA) was solvolyzed with polyethylene glycol (PEG) with different ratios of PLLA and PEG under dry conditions. The obtained materials were found to be the block copolymer of PLLA and PEG (PLLA/PEG) from NMR analysis of which the number average molecular weights ranged from 6 × 103 to 2 × 104 g mol−1. The films of stereocomplex (SC) of PLLA/PEG and poly-(d)-lactic acid (PDLA) were prepared by solvent casting method, and the thermal properties and the contact angle of the films were examined. The melting temperatures of PLLA/PEG and the corresponding SC with PDLA linearly decreased with the increase in the PEG content from 110 to 170 °C. The contact angle of PLLA/PEG became lower when the PEG content in the PLLA/PEG was higher, while their SCs with PDLA showed no clear correlation with the PEG content. Biodegradability of PLLA/PEGs and their SCs were also investigated with respect to the EG content.
Keywords: Polylactic acid; Stereocomplex; Solvolysis; Polyethylene glycol; Contact angle; Biodegradation;

Photo-oxidative stabilization of carbon nanotubes on polylactic acid by Giuliana Gorrasi; Andrea Sorrentino (963-971).
This paper aims to study the effect of multiwall carbon nanotubes (MWCNTs) on the photo-degradation behavior of polylactic acid (PLA) composites exposed to UV-light. The MWCNT dispersion state within the PLA matrix was analyzed by electrical conductivity measurements. From gel permeation chromatography it was verified that the rate of photo-degradation of PLA/MWCNT composites is lower than that of the unfilled PLA. The surface morphology modifications induced by UV have been analyzed by optical and scanning electron microscopy. Thermal analysis revealed an increase in the polymer crystallinity and a decrease in the degradation temperature during the UV treatment. The mechanical properties (Young's modulus and tensile strength at the yield point) were significantly increased by the addition of MWCNTs. However, the tensile strength and strain to failure slightly decreased with an increase in irradiation time. This complex behavior was attributed to a molecular reorganization in the first period of photo-aging followed by a severe macromolecular chain scission.
Keywords: Multiwall carbon nanotubes (MWCNTs); Photo-degradation; Polylactic acid (PLA) composites; Electrical conductivity; Thermal analysis; Mechanical properties;

Analysis of recycled PET bottles products by pyrolysis-gas chromatography by Nino Dimitrov; Ljerka Kratofil Krehula; Anita Ptiček Siročić; Zlata Hrnjak-Murgić (972-979).
The impact of the contaminants in post used PET bottles on the decomposition of polymer itself after recycling process was analyzed. For that reason sorption experiments of harmful substances to PET bottles were performed. In order to monitor the presence of contaminants in recycled PET and evolution of thermal decomposition products of samples: virgin PET, contaminated PET flakes (PET K) and recycled PET (PET RM) were studied. The thermal degradation products of PET were achieved by pyrolysis using Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS), temperature-programmed evolved gas analysis-mass spectrometry (EGA-MS) and thermogravimetric analysis (TGA). Reactive pyrolysis with tetramethyl ammonium hydroxide (TMAH) was also performed to gather additional information about degradation products in studied samples. The pyrolysis products analysis of the studied PET samples indicate some changes in decomposition mechanism of PET samples that pass through contamination process due to some diversity in their chemical and structural composition.
Keywords: Pyrolysis-gas chromatography; Evolved gas analysis; Reactive pyrolysis; Recycling of PET bottles; Poly(ethylene-terephthalate); Tetramethyl ammonium hydroxide;

Wool keratin-polypropylene composites: Properties and thermal degradation by Fabio Bertini; Maurizio Canetti; Alessia Patrucco; Marina Zoccola (980-987).
Wool fibres were submitted to green hydrolysis with superheated water in a microwave reactor, in view of potential valorisation of keratin-based wastes. The keratin hydrolysates containing free amino acids, peptides and low molecular weight proteins, were exploited as a biofiller in preparing polypropylene matrix composites. Maleic anhydride grafted polypropylene was used as a compatibilizer to promote dispersion of keratin. The thermal and mechanical properties were investigated in dependence of keratin and compatibilizer loadings, and related to morphological characteristics. The presence of keratin preserved the molecular weight of the polymer matrix during the processing and gave good overall mechanical properties to the compatibilized composites. The keratin hydrolysates strongly interfered on the crystallization behaviour and thermo-oxidative degradation of the polypropylene. The increase of polypropylene crystallization rate and the enhancement of thermal stability were observed as a function of the keratin amount in the compatibilized composites.
Keywords: Thermal degradation; Keratin; Polypropylene; Composites;

A new chitosan–ZnO/polyaniline (CPA–ZC/ZO) hybrid composite is prepared by single-step in situ oxidation polymerization of aniline hydrochloride in the presence of (NH4)2S2O8 and chitosan–ZnO (CS–ZO). The structural and morphological features of CPA and CPA–ZC/ZO hybrids were analyzed using FT-IR, UV–vis, SEM, EDXS and XRD analysis. The chemical bonding established between CPA and CPA–ZC/ZO, confirmed by FT-IR, is likely to be responsible for the enhanced chemical stability. The UV–vis spectra of CPA–ZC/ZO were found to red/blue shift as compared to those CPA molecular chains. From SEM observation, the ratio of ZnO nanoparticles to CPA altered the morphology of the hybrids from granular to plate like structure, which was confirmed by EDXS. The XRD patterns of the as-prepared hybrids show the wurtzite structure of ZnO is well maintained after the impregnation of CPA. Thermal property was studied using TG/DTA analysis shows the residual weight (TGA curves) and its weight derivative (DTA curves) of the CPA–ZC/ZO are more stable than CPA and CS–ZO. In addition, the cyclic voltammetry on the obtained hybrid materials revealed that the plate-like structure was more advantages for the electrochemical stability. Overall, the results show that the introduction of the ZnO nanoparticles into CPA matrix enhanced the thermal and electrode stability.
Keywords: Chitosan; ZnO; Polyaniline; Hybrid composite; Thermal stability;

Polyimides (PIs), used in satellites, are exposed to atomic oxygen (AO) irradiation and subjected to hypervelocity debris impacts which form residual tensile stresses and accelerated erosion.The objectives of this work are to study the PI's macromolecular structure and its deformation and erosion mechanisms when subjected to tensile stresses in an AO environment.The study shows that commercial PI is anisotropic, characterized by two main axis which are related to its semicrystalline structure. Under combined effects of stress and AO irradiation the PI's morphology was dependent on the direction of the applied stress and its magnitude. When the stress was applied parallel to the first main axis a carpet-like texture was formed. When the stress was however applied parallel to the second main axis an ordered surface was formed orthogonal to the direction of the applied stress.A mechanism which relates these findings to the PI macromolecular orientation is suggested.
Keywords: Polyimide; Macromolecular orientation; Stress; Atomic oxygen erosion;

The present work focuses on a study of the hydrolysis process of different commercial grades of polylactic acid (PLA). The aim was to evaluate the fundamental factors affecting hydrolysis in aqueous medium at 58 °C, namely the temperature indicated by the international standards for biodegradation during composting, and the kinetic constant of the reaction involved in such process. We analyzed samples of PLA with different d-isomer content, having amorphous and semi-crystalline structures. The hydrolysis process was followed, as function of the time, by means of different techniques: pH variation, variation of weight (%) of samples, crystallinity degree using DSC analysis, FTIR and WAXD investigation, molecular weights and molecular weight distribution by GPC analysis. The experimental data were used to describe the kinetic of hydrolysis phenomenon, assuming an autocatalytic mechanism.
Keywords: PLA; Hydrolysis; Autocatalytic mechanism; Degradation;

Characterization of tissue responses and degradation behavior of heparin-immobilized copolymer for drug-eluting stents by Li Shen; Zhenru Li; Feirong Gong; Feng Zhang; Qing Qin; Shujun Cheng; Junbo Ge (1015-1021).
It has been hypothesized that persistent presence of polymeric coating material may compromise the safety for drug-eluting stents, and that therefore a biodegradable coating might reduce late adverse events. In the present study, we explored the degradation behavior of heparin-immobilized copolymer of l-lactide (LA) and 5-methyl-5-benzyloxycarbonate-1,3-dioxan-2-one (MBC) coated stents and cast films by gel permeation chromatography (GPC), weight loss, light microscope, scanning electron microscope (SEM), and immunohistochemical staining in vitro and in vivo. The in vitro data indicated that the casting films lost 80% molecular weight and 20% of its mass within 16 weeks in PBS. The complete degradation of the coating material on the stent surface occurred within 16 weeks. The study also demonstrated similar degradation behaviors of the coating material in vivo conditions. There was no significant difference in extensive endothelialization and expression of inflammation-associated proteins such as monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), and CD3 after 4 weeks post stent implantation. So the heparin-immobilized copolymer is an excellent candidate material for drug-eluting stents given its lack of permanent existence after drug release and minimal in vivo tissue responses.
Keywords: Stent; Coating; Biodegradable; Tissue response;

In this paper, a novel hybrid organic–inorganic mesoporous silica was synthesized through co-condensation of vinyltriethoxysilane (VTES) and tetraethyl orthosilicate (TEOS) in the presence of poly(ethylene glycol)-B-poly(propylene glycol)-B-poly(ethylene glycol) (P123) surfactants, followed by DOPO modification via the reaction between vinyl groups and P–H bond in DOPO. The mesoscopic order and pore structure of the hybrid mesoporous silica was characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray diffraction (XRD) and N2 isothermal sorption. The effect of DOPO-grafted hybrid mesoporous silica (DM) and triphenyl phosphate (TPP) on the fire retardancy in polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) was examined by limiting oxygen index (LOI), UL-94 test, thermalgravity analysis (TGA) and cone calorimeter. Composite PC/ABS with loading of 2 wt% DM and 6 wt% TPP reached LOI value of 28% and V0 rating in UL-94 test. Present high residual weight in TGA and low heat release rate (HRR) in the cone calorimeter. It also indicated that DM is a synergistic agent with TPP, which improved the thermal stability and promoted the system giving dense char layer at high temperature.
Keywords: PC/ABS; Hybrid mesoporous silica; DOPO; Synergistic effect; Flame retardant;

In-depth radiative heat transmittance through polypropylene/nanoclay composites by Alberto Fina; Jie Feng; Fabio Cuttica (1030-1035).
In-depth heat absorption and material physical properties (thermal conductivity, melting temperature, melt viscosity etc) control the temperature profile across the thickness of a polymer specimen under external irradiance. In this work, the effect of nanoclays on the in-depth heat absorption is studied measuring the transmitted heat flux through a thin layer of material.Results showed that nanoclays reduce the heat transmitted through the composites, which is explained by the additional infrared absorbance of the nanoclays themselves and scattering.Transmitted heat was measured as a function of time, revealing different trends for the different compositions. In particular, the formation of bubbles in the range of 100 μm was observed in the presence of sodium montmorillonite and proved to be related to moisture release during the early stage of irradiation from the external heat source. The presence of such bubbles may scatter infrared radiation, resulting into a lower heat transmittance through the material.
Keywords: In-depth heat transmittance; In-depth heat absorbance; Nanoclay composites; Radiative heat scattering;

Synthesis of aromatic–aliphatic polyamide acting as adjuvant in polylactic acid (PLA)/ammonium polyphosphate (APP) system by Meisam Shabanian; Nian-Jun Kang; De-Yi Wang; Udo Wagenknecht; Gert Heinrich (1036-1042).
A potential adjuvant for polylactic acid (PLA)/ammonium polyphosphate (APP) system, a novel polyamide (PA) containing aromatic and aliphatic groups, was synthesized from a polycondensation reaction of adipic acid with 4,4-diaminodiphenyl sulphone. The synthesized PA was characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (1H NMR, 1 3C NMR), size exclusion chromatography (SEC) and thermogravimetric analysis (TGA), respectively. As a potential adjuvant, this PA has been used in a PLA system combined with and without APP in order to investigate the flame retardancy. The flammability of PLA and PA are studied by microscale combustion calorimeter (MCC). The flame retardant properties and thermal decomposition behaviors of PLA-PA composites were investigated by cone calorimeter test (CCT) and TGA, respectively. In the presence of APP, in some extent PA shows a synergistic effect on improving the flame retardancy of PLA composites at the fixed mass ratio 2:1 of APP and PA, reflecting delayed time to ignition (TTI) and slight decrease in the peak heat release rate (pHRR) in the cone calorimeter test. In order to further improve the flame retardancy, 1wt% clay was introduced to the PLA-PA-APP system while the total loading of additives kept at 15 wt%. The results of PLA-PA-APP-clay composite from cone calorimeter test showed significant decrease in heat release rate (HRR), total heat release rate (THR) and total smoke release (TSP).
Keywords: Flame retardancy; Polylactic acid (PLA); Polyamide; Synthesis and characterization; Adjuvant agent;

Flame retardant treatments of insulating agro-materials from flax short fibres by J. Lazko; N. Landercy; F. Laoutid; L. Dangreau; M.H. Huguet; O. Talon (1043-1051).
Improving fire resistance of lignocellulosic agro-materials is essential to extend their application domain. In this study, flame retardant agents, among which aluminium tri-hydroxide (ATH), zinc borate (ZB), melamine phosphate (MMP) and melamine borate (MMB), were incorporated in insulating materials based on flax short fibres. All flame retardant fillers were fixed firmly and permanently on the flax fibres using a protein binder. The incorporation was also homogeneous and preserved materials open porosity and expanded structure.Flame retardancy was characterized by Mass Loss cone calorimetry and UL 94 horizontal burning test. Materials morphology and thermal degradation were also investigated by scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA). Among all tested flame retardants, the best results were obtained with MMB. Immediate flame extinction was already achieved at 10 wt% loading rate, whereas the ignition time increased up to 6 times at 30 wt%, compared to the reference.
Keywords: Agro-materials; Flax short fibres; Pea proteins; Flame retardants; Combustion; Pyrolysis;

Characterization of the carbonization process of expandable graphite/silicone formulations in a simulated fire by B. Gardelle; S. Duquesne; P. Vandereecken; S. Bourbigot (1052-1063).
The fire performance of curable-silicone based coatings containing expandable graphite (EG) is evaluated in hydrocarbon fire scenario (standard UL1709) using a lab-scale furnace test. From 5% to 25% of expandable graphite is incorporated in the silicone matrix to make the coating swell during the fire experiment. Fire performance of 25%EG/silicone-based coating is better than that of commercial intumescent paint used as reference. This is explained by a high swelling velocity (18%/s), a high expansion (3400%), an impressive cohesion of the char and a low heat conductivity at high temperature (0.35 W/K m at 500 °C). To elucidate this way of charring, the residue after fire testing was analyzed by scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, X-ray photoelectron spectroscopy and X-ray diffraction. It is shown that the char is composed of two main parts: the top is composed of quartz and amorphous silica which coat graphite flakes and the heart of the char is composed of graphite flakes embedded in degraded silicone forming a complex structure. It is shown that, the good cohesion of the char is due to: (i) the presence of the undegraded silicone matrix; and (ii) the coating of graphite pellets by silicone.
Keywords: Silicone; Resistance to fire; Expandable graphite; Thermal conductivity;

Xylan esters as bio-based nucleating agents for poly (l-lactic acid) by Noreen Grace V. Fundador; Yukiko Enomoto-Rogers; Akio Takemura; Tadahisa Iwata (1064-1071).
Xylan esters of varying alkyl chain lengths (C2–C12) were screened for their effect on the crystallization of poly(l-lactic acid) (PLLA). Among the xylan esters, only xylan propionate (XylPr) and xylan butyrate (XylBu) exhibited a nucleating effect on PLLA during non-isothermal crystallization. Blending of 1% XylPr or XylBu with PLLA led to a decrease in the crystallization temperature (T c ) of PLLA from 125 °C to 96 or 97 °C, respectively. Similar results were also obtained for 0.1% blends of the same ester. Isothermal crystallization studies revealed that the PLLA blends exhibited faster crystallization rates, higher crystallinities and smaller spherulites than neat PLLA. Consequently, the PLLA blends possessed lower degrees of haze than neat PLLA and their thermal expansion values were also lower than that of neat PLLA when heated above their glass transition temperature (60 °C), indicating their resistance to heat deformation. The mechanism of nucleation was proposed based from the WAXD analysis results.
Keywords: Crystallization; Nucleating agents; Xylan esters; Poly(l-lactic acid);

Depolymerization of alginate was accessed, for the first time, by the plasma treatment in solution called solution plasma process (SPP). The process was done by applying an electrical discharge into a reactor containing sodium alginate aqueous solution. The key of the production is the generation of reactive species induced by the plasma in a liquid environment that can lead to the scission of polymer chains. Effect of polymer concentration on the SPP processing parameters and the depolymerization efficiency were studied. Three concentrations of sodium alginate solutions, i.e., 0.2, 0.5, and 0.9 %w/v, were prepared. The results showed that increasing concentration of the alginate solution decreased the applied voltage required for the generation of plasma. Optical emission spectra demonstrated that the generation of reactive species was the highest at the lowest alginate concentration (i.e. 0.2 %w/v). Therefore, molecular weight reduction of this concentration after the SPP was more remarkable than the others. The most significant species required for the depolymerization of alginate was the reactive hydrogen species. Molecular weight distributions (MWD) of the obtained low molecular weight alginates (LMALGs) for all concentrations were narrow. Furthermore, reduction trends of molecular weight and viscosity of alginate with varying operation times indicated that the depolymerization of alginate in aqueous solution by the SPP was affected by the combined contribution of two factors: (1) the amount of reactive species generated during the process and (2) the degree of chain entanglement of the polymers.
Keywords: Chain entanglement; Depolymerization; Sodium alginate; Solution plasma process;

Co-oxidation kinetic model for the thermal oxidation of polyethylene-unsaturated substrate systems by Emmanuel Richaud; Bruno Fayolle; Jacques Verdu; Jozef Rychlý (1081-1088).
The thermal oxidation of polyethylene (PE) impregnated by the methyl esters of unsaturated fatty acids (UFEs) was studied using chemiluminescence, and infra-red spectrophotometry. It was shown that the presence of UFEs accelerates the PE aging process. This can be interpreted as a co-oxidation phenomenon. In this study, the previously established models for PE and UFEs self-oxidation have been coupled in order to develop a co-oxidation model. Using the existing rate constants for the PE and UFEs self-oxidations, this model can simulate the complex shape of the kinetic curves of PE-UFE co-oxidation.
Keywords: Polyethylene; Methyl esters of unsaturated fatty acids; Co-oxidation; Kinetic modeling; Chemiluminescence;

One of the most attractive characteristics of poly(lactic acid) (PLA) is the fact that, following the international standards for polymer biodegradation, it can be potentially degraded in soil or compost. The potential of this material, however, requires additional investigations in order to understand the PLA behaviour during composting, including the main factors that affect the biodegradation phenomena. In this work, the degradation of PLA was investigated in both distilled water and controlled composting conditions at a temperature of 58 °C. PLA samples with different morphologies were prepared by injection moulding and successive annealing at high temperature. As expected, the crystallinity was found to decrease the PLA degradation rate, but it was also found that the crystallinity affects only partially the first stages of water diffusion in the polymer matrix, whereas it has a significant effect on the final swelling of the samples and on their biodegradation rate. It could therefore be concluded that the denser structure of the initially crystalline sample was more impermeable to the enzymatic attach and to oligomer diffusion. This was also testified by the fact that if the characteristic dimension of the crystalline sample is reduced, degradation rate becomes much faster and close (although still slower) to that of the amorphous sample.
Keywords: Poly(lactic acid) (PLA); Biodegradation in compost; Morphologies; Water diffusion;

The melt stability of star-shaped stereocomplex polylactide with different core structure by tripentaerythritol (TPE) and polyhedral oligomeric silsesquioxane-octahydroxypropyldimethylsilyl (POSS(OH)8) compounds was investigated. The three-dimensional (3D) core structures affect the ability of star-shaped stereocomplex polylactide to preserve stereocomplex crystallite after melted. The exact position and proper space distribution of arm result in low chain freedom of itself which affects the ability of each arm to reassemble stereocomplex crystallites after melted. The result confirmed that the inorganic POSS(OH)8 core molecule has better support to maintain melt stability compare to TPE core.
Keywords: Melt stability; Polylactide; Stereocomplex; Star polymers; Structure;