Preparation, characterization and biodegradation of biopolymer nanocomposites based on fumed silica

Review of sustainable, eco-friendly, and conductive polymer nanocomposites for electronic and thermal applications: current status and future prospects

Biodegradable polymer nanocomposites (BPNCs) are advanced materials that have gained significant attention over the past 20 years due to their advantages over conventional polymers. BPNCs are eco-friendly, cost-effective, contamination-resistant, and tailorable for specific applications. Nevertheless, their usage is limited due to their unsatisfactory physical and mechanical properties. To improve these properties, nanofillers are incorporated into natural polymer matrices, to enhance mechanical durability, biodegradability, electrical conductivity, dielectric, and thermal properties. Despite the significant advances in the development of BPNCs over the last decades, our understanding of their dielectric, thermal, and electrical conductivity is still far from complete. This review paper aims to provide comprehensive insights into the fundamental principles behind these properties, the main synthesis, and characterization methods, and their functionality and performance. Moreover, the role of nanofillers in strength, permeability, thermal stability, biodegradability, heat transport, and electrical conductivity is discussed. Additionally, the paper explores the applications, challenges, and opportunities of BPNCs for electronic devices, thermal management, and food packaging. Finally, this paper highlights the benefits of BPNCs as biodegradable and biodecomposable functional materials to replace traditional plastics. Finally, the contemporary industrial advances based on an overview of the main stakeholders and recently commercialized products are addressed.

Synthesis and Characterization of ABA-Type Triblock Copolymers Using Novel Bifunctional PS, PMMA, and PCL Macroinitiators Bearing p-xylene-bis(2-mercaptoethyloxy) Core

Syntheses of novel bifunctional poly(methyl methacrylate) (PMMA)-, poly(styrene) (PS)-, and (poly ε-caprolactone) (PCL)-based atom transfer radical polymerization (ATRP) macroinitiators derived from p-xylene-bis(1-hydroxy-3-thia-propanoloxy) core were carried out to obtain ABA-type block copolymers. Firstly, a novel bifunctional ATRP initiator, 1,4-phenylenebis(methylene-thioethane-2,1-diyl)bis(2-bromo-2-methylpropanoat) (PXTBR), synthesized the reaction of p-xylene-bis(1-hydroxy-3-thia-propane) (PXTOH) with α-bromoisobutryl bromide. The PMMA and PS macroinitiators were prepared by ATRP of methyl methacrylate (MMA) and styrene (S) as monomers using (PXTBR) as the initiator and copper(I) bromide/N,N,N',N″,N″-pentamethyldiethylenetriamine (CuBr/PMDETA) as a catalyst system. Secondly, di(α-bromoester) end-functionalized PCL-based ATRP macronitiator (PXTPCLBr) was prepared by esterification of hydroxyl end groups of PCL-diol (PXTPCLOH) synthesized by Sn(Oct)2-catalyzed ring opening polymerization (ROP) of ε-CL in bulk using (PXTOH) as initiator. Finally, ABA-type block copolymers, PXT(PS-b-PMMA-b-PS), PXT(PMMA-b-PS-b-PMMA), PXT(PS-b-PCL-b-PS), and PXT(PMMA-b-PCL-b-PMMA), were synthesized by ATRP of MMA and S as monomers using PMMA-, PS-, and PCL-based macroinitiators in the presence of CuBr/PMDETA as the catalyst system in toluene or N,N-dimethylformamide (DMF) at different temperatures. In addition, the extraction abilities of PCL and PS were investigated under liquid-liquid phase conditions using heavy metal picrates (Ag+, Cd2+, Cu2+, Hg2+, Pb2+, and Zn2+) as substrates and measuring with UV-Vis the amounts of picrate in the 1,2-dichloroethane phase before and after treatment with the polymers. The extraction affinity of PXTPCL and PXTPS for Hg2+ was found to be highest in the liquid-liquid phase extraction experiments. Characterizations of the molecular structures for synthesized novel initiators, macroinitiators, and the block copolymers were made by spectroscopic (FT-IR, ESI-MS, 1H NMR, 13C NMR), DSC, TGA, chromatographic (GPC), and morphologic SEM.

Gut Microbiome Associating with Carbon and Nitrogen Metabolism during Biodegradation of Polyethene in Tenebrio larvae with Crop Residues as Co-Diets

Tenebrio molitor and Tenebrio obscurus (Coleoptera: Tenebrionidae) larvae are two commercial insects that eat plant and crop residues as diets and also biodegrade synthetic plastics polyethylene (PE). We examined biodegradation of low-density PE (LDPE) foam (M_n = 28.9 kDa and M_w = 342.0 kDa) with and without respective co-diets, i.e., wheat brain (WB) or corn flour (CF), corn straw (CS), and rice straw (RS) at 4:1 (w/w), and their gut microbiome and genetic metabolic functional groups at 27.0 ± 0.5 °C after 28 days of incubation. The presence of co-diets enhanced LDPE consumption in both larvae and broad-depolymerized the ingested LDPE. The diet type shaped gut microbial diversity, potential pathways, and metabolic functions. The sequence of effectiveness of co-diets was WB or CF > CS > RS for larval development and LDPE degradation. Co-occurrence networks indicated that the larvae co-fed with LDPE displayed more complex correlations of gut microbiome than the larvae fed with single diets. The primary diet of WB or CF and crop residues CS and RS provided energy and nitrogen source to significantly enhance LDPE biodegradation with synergistic activities of the gut microbiota. For the larvae fed LDPE and LDPE plus co-diets, nitrogen fixation function was stimulated compared to normal diets and associated with LDPE biodegradation.

Preparation and properties of environmentally benign waterborne polyurethane composites from sodium-alginate-modified nano calcium carbonate

Well-dispersed inorganic nanoparticles in organic polymers are critical in the preparation of high-performance nanocomposites. This study prepared a series of waterborne polyurethane (WPU)/calcium carbonate nanocomposites using the solution blending method. Next, FT-IR, TG-DTG and XRD tests were carried out to confirm that the biopolymer sodium alginate (SA) was successfully encapsulated on the surface of the calcium carbonate nanoparticles, and that SA achieved satisfactory surface modification of the calcium carbonate nanoparticles. The Zeta and ultraviolet (UV) absorbance test results reveal that SA-modified nano calcium carbonate (MCC) had good dispersion stability in water. The effects of the MCC dosage on the composite mechanical properties, thermal stability, and cross-sectional morphology observed by scanning electron microscopy, and the water resistance of the nanocomposite were investigated. The results reveal that the incorporation of 3wt% of MCC in WPU had stable distribution, which led to a 54% increase in the tensile strength of the nanocomposite, while maintaining excellent elongation at break (2187%) and increasing the maximum decomposition temperature to 419.6 °C. Importantly, the improved water resistance facilitates the application of this environmentally benign composite material in humid environments.

Effect of the Addition of Nano-Silica and Poly(ε-caprolactone) on the Mechanical and Thermal Properties of Poly(lactic acid) Blends and Possible Application in Embossing Process

In this study, the mechanical and thermal properties of poly(lactic acid) (PLA) blends with an addition of poly(ε-caprolactone) (PCL) and fumed silica (SiO₂) were evaluated to research the possibility of their use as relief printing plates for embossing processes. PCL and nano-silica were added to the PLA matrix at different concentrations. Morphological, thermal and mechanical analyses were performed to determine the properties and possible functional characteristics of the studied blends. SEM micrographs showed that unmodified PLA/PCL blends exhibit a morphology typical of incompatible blends with clearly visible spherical domains of dispersed PCL in PLA. In particular, the results of the hardness tests showed that the selected blends have the optimal hardness (between 65 SH D and 75 SH D) for use in the embossing process. The tensile tests showed that the addition of nano-silica to neat PLA and to the PLA/PCL blends 50/50 and 60/40 improved the mechanical properties of the blends, especially stiffness and toughness. The DMA results showed that the addition of smaller amounts of SiO₂ can contribute to an increase in storage modulus, which is due to good dispersion and distribution of SiO₂ in the matrix. DSC analysis showed that the addition of PCL to PLA polymer increased the thermal stability of PLA and that the addition of nano-silica increased the degree of crystallinity of PLA. The TGA results showed that the addition of nano-silica improved the thermal degradation behavior of the studied blends, especially for blends modified with 3 wt% nano-silica. The results show that it is possible to optimize the mechanical and thermal properties of the blends with the aim of using them in the embossing process.

Multi-biofunctional graphene oxide-enhanced poly-L-lactic acid composite nanofiber scaffolds for ovarian function recovery of transplanted-tissue

In this study, we successfully constructed the new graphene oxide/poly-L-lactic acid (GO/PLLA) nanofiber scaffolds with a hydrophilic surface and porous network structure that were highly favorable for cell infiltration. When employed these new nanofiber scaffolds for a wide range of tissue engineering applications, it was expected to promote graft tissue survival and angiogenesis. The new GO/PLLA nanofiber scaffold with an appropriate concentration of 1.0 wt% was applied for the restoration of ovarian function and reserve in mice with primary ovarian insufficiency (POI). After co-transplanting the normal ovarian cortex loaded on these new nanomaterials into the in situ ovarian tissue of POI mice, the fusion of transplanted ovarian cortex with damaged ovarian tissue was improved, as well as the ovarian function and the follicle numbers. Moreover, angiogenesis was observed clearly and proved to exist in the transplanted tissue and nanomaterials, with the most conspicuous effect after co-transplantation with 1.0 wt% GO/PLLA nanofiber scaffold. In addition, nitric oxide (NO) production by phosphorylated endothelial nitric oxide synthase (p-eNOS) in vivo was proven to be involved in the effect of GO and PLLA on the improved survival rate of the transplanted ovarian cortex. This study provides a new method for the fertility preservation of ovarian tissue cryopreservation and transplantation, as well as a new strategy for the transplantation of other organs.

A Comprehensive Investigation of the Structural, Thermal, and Biological Properties of Fully Randomized Biomedical Polyesters Synthesized with a Nontoxic Bismuth(III) Catalyst

Aliphatic polyesters are the most common type of biodegradable synthetic polymer used in many pharmaceutical applications nowadays. This report describes the ring-opening polymerization (ROP) of l-lactide (L-LA), ε-caprolactone (CL) and glycolide (Gly) in the presence of a simple, inexpensive and convenient PEG200-BiOct₃ catalytic system. The chemical structures of the obtained copolymers were characterized by ¹H- or ¹³C-NMR. GPC was used to estimate the average molecular weight of the resulting polyesters, whereas TGA and DSC were employed to determine the thermal properties of polymeric products. The effects of temperature, reaction time, and catalyst content on the polymerization process were investigated. Importantly, the obtained polyesters were not cyto- or genotoxic, which is significant in terms of the potential for medical applications (e.g., for drug delivery systems). As a result of transesterification, the copolymers obtained had a random distribution of comonomer units along the polymer chain. The thermal analysis indicated an amorphous nature of poly(l-lactide-co-ε-caprolactone) (PLACL) and a low degree of crystallinity of poly(ε-caprolactone-co-glycolide) (PCLGA, X_c = 15.1%), in accordance with the microstructures with random distributions and short sequences of comonomer units (l = 1.02-2.82). Significant differences in reactivity were observed among comonomers, confirming preferential ring opening of L-LA during the copolymerization process.

Nanoparticle Shape Influence over Poly(lactic acid) Barrier Properties by Molecular Dynamics Simulations

Climate change is leading us to search for new materials that allow a more sustainable environmental situation in the long term. Poly(lactic acid) (PLA) has been proposed as a substitute for traditional plastics due to its high biodegradability. Various components have been added to improve their mechanical, thermal, and barrier properties. The modification of the PLA barrier properties by introducing nanoparticles with different shapes is an important aspect to control the molecular diffusion of oxygen and other gas compounds. In this work, we have described changes in oxygen diffusion by introducing nanoparticles of different shapes through molecular dynamics simulations. Our model illustrates that the existence of curved surfaces and the deposition of PLA around them by short chains generate small holes where oxygen accumulates, forming clusters and reducing their mobility. From the several considered shapes, the sphere is the most suitable structure to improve the barrier properties of the PLA.

Confirmation of biodegradation of low-density polyethylene in dark- versus yellow- mealworms (larvae of Tenebrio obscurus versus Tenebrio molitor) via. gut microbe-independent depolymerization

Tenebrio obscurus (Coleoptera: Tenebrionidae) larvae are capable of biodegrading polystyrene (PS) but their capacity for polyethylene (PE) degradation and pattern of depolymerization remains unknown. This study fed the larvae of T. obscurus and Tenebrio molitor, which have PE degrading capacity, two commercial low-density PE (LDPE) foams i.e., PE-1 and PE-2, with respective number-average molecular weights (M_n) of 28.9 and 27.3 kDa and weight-average molecular weights (M_w) of 342.0 and 264.1 kDa, over a 36-day period at ambient temperature. The M_w of residual PE in frass (excrement) of T. obscurus, fed with PE-1 and PE-2, decreased by 45.4 ± 0.4% and 34.8 ± 0.3%, respectively, while the respective decrease in frass of T. molitor was 43.3 ± 0.5% and 31.7 ± 0.5%. Data analysis showed that low molecular weight PE (<5.0 kDa) was rapidly digested while longer chain portions (>10.0 kDa) were broken down or cleaved, indicating a broad depolymerization pattern. Mass balance analysis indicated nearly 40% of ingested LDPE was digested to CO₂. Antibiotic suppression of gut microbes in T. molitor and T. obscurus larvae with gentamicin obviously reduced their gut microbes on day 15 but did not stop depolymerization because the M_n, Mw and size- average molecular weight (M_z) decreased. This confirmed that LDPE biodegradation in T. obscurus was independent of gut microbes as observed during previous PS degradation in T. molitor, suggesting that the intestinal digestive system could perform LDPE depolymerization. High-throughput sequencing revealed significant shifts in the gut microbial community during bran-fed and unfed conditions in response to LDPE feeding in both Tenebrio species. The respective predominant gut genera of Spiroplasma sp. and Enterococcus sp. were observed in LDPE-fed T. molitor and T. obscurus larvae.

A Review on Synthesis, Properties, and Applications of Polylactic Acid/Silica Composites

Polylactic acid (PLA)/silica composites as multifunctional high-performance materials have been extensively examined in the past few years by virtue of their outstanding properties relative to neat PLA. The fabrication methods, such as melt-mixing, sol–gel, and in situ polymerization, as well as the surface functionalization of silica, used to improve the dispersion of silica in the polymer matrix are outlined. The rheological, thermal, mechanical, and biodegradation properties of PLA/silica nanocomposites are highlighted. The potential applications arising from the addition of silica nanoparticles into the PLA matrix are also described. Finally, we believe that a better understanding of the role of silica additive with current improvement strategies in the dispersion of this additive in the polymer matrix is the key for successful utilization of PLA/silica nanocomposites and to maximize their fit with industrial applications needs.

Ecofriendly biopolymers and composites: Preparation and their applications in water-treatment

Over the past few decades, the term polymer has been repeatedly used in several industries for their immense characteristics in different applications. Polymers and their composites which were prepared from chemical monomer sources turned out to be potentially harmful to the environment due to their tedious degradation process. Biopolymers are natural substitutes for synthetic polymers which can be efficiently extricated from natural sources. They are predominantly available as polymeric units as well as monomeric units that are linked covalently. These environment-friendly biopolymers and their composites can be categorized based on their numerous sources, different methods of preparation and their potential form of usage. They were found to be biocompatible and biodegradable which make them exceptionally useful in environment based applications, mainly in the process of water treatment, both potable and wastewater. Further, the biopolymer and biopolymer composites easily fit into different parts of the treatment process by acting as filtration media, adsorbents, coagulants and as flocculants. The primary focus of this review is to provide a comprehensive information of biopolymers and biopolymer composites from synthesis to their usefulness for their productive application in water treatment processes. On the whole, it can be substantiated that the biopolymers were identified to play a notable adversary to the synthetic polymers in treating waters with an indispensable need for an elaborative study in the production of the biopolymers.

Biodegradable polymers as carriers for tuning the release and improve the herbicidal effectiveness of Dittrichia viscosa plant organic extracts

BACKGROUND

The organic extracts (OEs) of Dittrichia viscosa, a ruderal plant common in the Mediterranean regions, proved to have herbicidal properties. In order to improve OE effectiveness and to develop novel eco-friendly bioherbicidal products, different amounts of OE were included in poly(butylene succinate)- and polycaprolactone-based films (PBS and PCL, respectively). Particular attention was given to the study of interactions between the polymers and OEs, with a deep spotlight concerning the influence of OEs on structural, morphological and thermal properties of both polymers, in order to assess the OE releasing kinetics from the matrices and its tuned herbicidal action against seeds.

RESULTS

The bioassays carried out on Lepidium sativum and Phelipanche ramosa seeds evidenced a more controlled and effective OE release by PBS than PCL, and a longer lasting efficacy by the polymers with a higher OE content. The chemical-physical analyses were performed on films before and after biological assays. The thermogravimetric analysis confirmed that OE was a thermal stabilizer of the polymer; the presence of OE and polymer separated degradative kinetics suggested that only a partial and functional miscibility between polymers and OE occurred. The morphological analysis confirmed the good OE dispersion between PBS and PCL molecular chains. Infrared spectroscopy highlighted the enhanced hydrolysed structure of the doped polymers after the bioassays. These outcomes well matched the quantitative information outlined by release kinetics.

DISCUSSION

The use of biodegradable polymers allows the effectiveness and tuning of the release of the formulated bioactive compounds to be improved. The easy-to-obtain and easy-to-formulate OE could become a suitable and environmentally friendly instrument in weed management programmes.

Degradation of Polylactic Acid Using Sub-Critical Water for Compost

Polylactic acid (PLA) is expected to replace many general-purpose plastics, especially those used for food packaging and agricultural mulch. In composting, the degradation speed of PLA is affected by the molecular weight, crystallinity, and microbial activity. PLA with a molecular weight of less than 10,000 has been reported to have higher decomposition rates than those with higher molecular weight. However, PLA degradation generates water-soluble products, including lactic acid, that decrease the pH of soil or compost. As acidification of soil or compost affects farm products, their pH should be controlled. Therefore, a method for determining suitable reaction conditions to achieve ideal decomposition products is necessary. This study aimed to determine suitable reaction conditions for generating preprocessed PLA with a molecular weight lower than 10,000 without producing water-soluble contents. To this end, we investigated the degradation of PLA using sub-critical water. The molecular weight and ratio of water-soluble contents (WSCs) affecting the pH of preprocessed products were evaluated through kinetic analysis, and crystallinity was analyzed through differential scanning calorimetry. Preprocessed PLA was prepared under the determined ideal conditions, and its characteristics in soil were observed. The results showed that the crystallization rate increased with PLA decomposition but remained lower than 30%. In addition, the pH of compost mixed with 40% of preprocessed PLA could be controlled within pH 5.4–5.5 over 90 days. Overall, soil mixed with the preprocessed PLA prepared under the determined ideal conditions remains suitable for plant growth.

Role of Surface-Treated Silica Nanoparticles on the Thermo-Mechanical Behavior of Poly(Lactide)

Surface-treated fumed silica nanoparticles were added at various concentrations (from 1 to 24 vol%) to a commercial poly(lactide) or poly(lactic acid) (PLA) matrix specifically designed for packaging applications. Thermo-mechanical behavior of the resulting nanocomposites was investigated. Field Emission Scanning Electron Microscopy (FESEM) micrographs revealed how a homogeneous nanofiller dispersion was obtained even at elevated filler amounts, with a positive influence of the thermal degradation stability of the materials. Modelization of Differential Scanning Calorimetry (DSC) curves through the Avrami–Ozawa model demonstrated that fumed silica nanoparticles did not substantially affect the crystallization behavior of the material. On the other hand, nanosilica addition was responsible for significant improvements of the storage modulus (E′) above the glass transition temperature and of the Vicat grade. Multifrequency DMTA tests showed that the stabilizing effect due to nanosilica introduction could be effective over the whole range of testing frequencies. Sumita model was used to evaluate the level of filler dispersion. The obtained results demonstrated the potential of functionalized silica nanoparticles in improving the thermo-mechanical stability of biodegradable matrices for packaging applications, especially at elevated service temperatures.

Enhanced cluster order-disorder transition-induced dilatancy in silane-functionalized nanosilica colloids

Herein, we report a novel nanosilica-based shear-thickening fluid, whose shear-thickening performance has been largely augmented by surface functionalizing silica employing silane chains. The functionalized shear-thickening colloids were transparent; this suggested that they have promise for application. An enhancement in viscosity was observed by over an order of magnitude by the usage of functionalized particles, which could be explained on the basis of enhanced hydroclustering and an order-to-disorder transition of the particles due to physical bonding of the silane with the base polymer. It was also observed that the shear-thickening behavior was grossly modified due to the presence of the functionalized nanoparticles. Oscillatory analysis showed that the functionalized colloids exhibited an improved dynamic response, with enhanced elastic behavior under variant strain and frequency conditions. Additionally, impact resistance tests revealed that the thickening of the viscosity upon impact was augmented by over an order of magnitude; this established these functionalized colloids as excellent candidates for liquid armors. The viscoelastic behavior was modeled based on the Cox-Merz formalism. Additionally, three-element viscoelastic modeling was performed, and it was observed that while the silica-based colloids conformed to the predominantly viscous model, the functionalized system transited to a predominantly elastic model. The present article can have important implications for the design and engineering of shear-thickening fluids employing nanomaterials.

Surface modified SiO2 nanoparticles by thiamine and ultrasonication synthesis of PCL/SiO2-VB1 NCs: Morphology, thermal, mechanical and bioactivity investigations

The influence of silica (SiO₂) nanoparticles (NPs) on the properties of polycaprolactone (PCL) was investigated. Due to the intense tendency of SiO₂ NPs to aggregation and their high surface energy, the surface of SiO₂ NPs was treatment via Vitamin B₁ (VB₁) as a biosafe coupling agent. Novel PCL/SiO₂-VB₁ nanocomposites (NC) films by variety of percentage of SiO₂-VB₁ NPs were prepared under ultrasonic irradiation as an eco-friendly and fast procedure following by casting method. Fourier transform infrared spectroscopy and energy dispersive X-ray analysis exposed the presence of SiO₂ NPs into the polymer matrix. A good distribution of the silica into the polymer matrix was detected by microscopic observations and EDX testing. According to the UV-Vis spectra, the absorption of prepared NCs was improved via increasing the amount of SiO₂ NPs. PCL/SiO₂-VB₁ NCs showed more thermal stability compared to the pure polymer. The tensile test was investigated and good arrangement among the experimental data and the predicted flexibility of NCs was obtained. Moreover, PCL/SiO₂-VB₁ 6wt% had noticeable increase values for tensile strength. Finally, in vitro bioactivity investigation designated that by rising SiO₂ contents in the NCs, the amount of the hydroxyapatite formed was increased and NC films are bioactive and have a potential to be utilized in bone tissue engineering.

Studies on Electrical, Thermal and Corrosion Behaviour of Cashew Tree Gum Grafted Poly(Acrylamide)

The present work aimed to study the thermal transitions, electrical properties and corrosion behaviour of cashew tree gum (CTG), poly (acrylamide) (PAM) and cashew tree gum grafted poly (acrylamide) (CTG-g-PAM) copolymer. Various amounts of acrylamide monomer were grafted onto cashew gum using a radical polymerization method. The formation of graft copolymer was analysed by FTIR, UV, SEM, DSC and electrical conductivity measurements. The FTIR and UV spectrum infers the occurrence of strong intermolecular interaction between cashew gum and poly (acrylamide). SEM photographs revealed that the acrylamide unit was well inserted into the cashew gum segments. The DSC analysis showed a significant decrease in glass transition temperature with an increase in amount of acrylamide chains. CTG shows higher AC conductivity than PAM and the conductivity of graft copolymer increases with the concentration of acrylamide up to certain concentration of monomer and thereafter the value decreases. The dielectric properties such as dielectric constant and dielectric loss tangent values of PAM was lower than CTG and the dielectric values also shows a similar trend as AC conductivity. CTG, PAM and its graft copolymer with various amount of poly (acrylamide) have been investigated as a corrosion inhibition for mild steel in hydrochloric acid. The inhibition efficiency increased with increase in concentration of PAM in the graft copolymer. PAM was found to have the high inhibition efficiency than CTG, due to the difference in their molecular structures. The corrosion rate of all the samples enhanced with the raise in temperature whereas the inhibition efficiency deceases.

Physical, Mechanical, and Thermal Analysis of Polylactic Acid/Fumed Silica/Clay (1.28E) Nanocomposites

Polylactic acid/fumed silica/clay (PLA/FS/clay) (1.28E) nanocomposites have been successfully prepared by solution-intercalation film-casting technique. The resultant nanocomposites were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), tensile test, thermogravimetric analysis (TGA), and moisture absorption test. The FT-IR spectrum indicated that PLA/FS/clay with 2 wt% had much broader peak compared to 5 wt%, 10 wt%, and 15 wt% nanocomposites. Incorporation of clay (1.28E) with 2 wt% showed the best compatibility with PLA/FS matrix. PLA/FS/clay (1.28E) nanocomposite with 2 wt% of clay loading had higher tensile strength and modulus compared to other nanocomposites. The thermal stability and activation energy of 2 wt% of PLA/FS/clay (1.28E) nanocomposite are the highest among all the nanocomposites. The moisture absorbed into PLA/FS/clay (1.28E) nanocomposite was significantly reduced with clay loading of 2 wt%.

Porous polylactic acid-silica hybrids: preparation, characterization, and study of mesenchymal stem cell osteogenic differentiation

A novel approach to reinforce polymer porous membranes is presented. In the prepared hybrid materials, the inorganic phase of silica is synthesized in-situ and inside the pores of aminolyzed polylactic acid (PLA) membranes by sol-gel reactions using tetraethylorthosilicate (TEOS) and glycidoxypropyltrimethoxysilane (GPTMS) as precursors. The hybrid materials present a porous structure with a silica layer covering the walls of the pores while GPTMS serves also as coupling agent between the organic and inorganic phase. The adjustment of silica precursors ratio allows the modulation of the thermomechanical properties. Culture of mesenchymal stem cells on these supports in osteogenic medium shows the expression of characteristic osteoblastic markers and the mineralization of the extracellular matrix.

Identification of important abiotic and biotic factors in the biodegradation of poly(l-lactic acid)

The biodegradation of four poly(l-lactic acid) (PLA) samples with molecular weights (MW) ranging from approximately 34 to 160kgmol(-1) was investigated under composting conditions. The biodegradation rate decreased, and initial retardation was discernible in parallel with the increasing MW of the polymer. Furthermore, the specific surface area of the polymer sample was identified as the important factor accelerating biodegradation. Microbial community compositions and dynamics during the biodegradation of different PLA were monitored by temperature gradient gel electrophoresis, and were found to be virtually identical for all PLA materials and independent of MW. A specific PLA degrading bacteria was isolated and tentatively designated Thermopolyspora flexuosa FTPLA. The addition of a limited amount of low MW PLA did not accelerate the biodegradation of high MW PLA, suggesting that the process is not limited to the number of specific degraders and/or the induction of specific enzymes. In parallel, abiotic hydrolysis was investigated for the same set of samples and their courses found to be quasi-identical with the biodegradation of all four PLA samples investigated. This suggests that the abiotic hydrolysis represented a rate limiting step in the biodegradation process and the organisms present were not able to accelerate depolymerization significantly by the action of their enzymes.