Poly(methyl methacrylate)-induced Microstructure and Hydrolysis Behavior Changes of Poly(L-lactic acid)/Carbon Nanotubes Composites

Poly(L-lactic acid)(PLLA)-based composites exhibit wide applications in many fields.However,most of hydrophilic fillers usually accelerate the hydrolytic degradation of PLLA,which is unfavorable for the prolonging of the service life of the articles.In this work,a small quantity of poly(methyl methacrylate)(PMMA)(2 wt%-10 wt%)was incorporated into the PLLA/carbon nanotubes(CNTs)composites.The effects of PMMA content on the dispersion of CNTs as well as the microstructure and hydrolytic degradation behaviors of the composites were systematically investigated.The results showed that PMMA promoted the dispersion of CNTs in the composites.Amorphous PLLA was obtained in all the composites.Largely enhanced hydrolytic degradation resistance was achieved by incorporating PMMA,especially at relatively high PMMA content.Incorporating 10 wt%PMMA led to a dramatic decrease in the hydrolytic degradation rate from 0.19%/h of the PLLA/CNT composite sample to 0.059%/h of the PLLA/PMMA-10/CNT composite sample.The microstructure evolution of the composites was also detected,and the results showed that no crystallization occurred in the PLLA matrix.Further results based on the interfacial tension calculation showed that the enhanced hydrolytic degradation resistance of the PLLA matrix was mainly attributed to the relatively strong interfacial affinity between PMMA and CNTs,which prevented the occurrence of hydrolytic degradation at the interface between PLLA and CNTs.This work provides an alternative method for tailoring the hydrolytic degradation ability of the PLLA-based composites.     

Greatly enhanced hydrolytic degradation ability of poly(L-lactide) achieved by adding poly(ethylene glycol)

Plasticized poly(L-lactide)(PLLA) materials have been applied in many fields and the microstructure performance of such materials attracts much attention of researchers. However, few reports declared the hydrolytic degradation ability of the plasticized PLLA materials. In this article, a small quantity of poly(ethylene glycol)(PEG) was introduced into PLLA, which aimed to understand the hydrolytic degradation behavior of the plasticized PLLA materials. The microstructures of the plasticized samples were comparatively investigated using scanning electron microscopy(SEM), wide angle X-ray diffraction(WAXD), differential scanning calorimetry(DSC) and Flourier transform infrared spectroscopy(FTIR), etc. The results demonstrated that PEG improved the hydrophilicity of sample surface, and the relatively high content of PEG enhanced the crystallization ability of PLLA matrix. The hydrolytic degradation measurement was carried out at 60 ℃ in an alkaline solution of pH = 12. The results demonstrated that the plasticized PLLA samples exhibited accelerated hydrolytic degradation compared with the pure PLLA sample, and the hydrolytic degradation was also dependent on the PEG content. Further results demonstrated that PEG induced the change of hydrolytic degradation mechanism possibly due to the good dissolution ability of PEG in water, which provided more paths for the penetration of water. Furthermore, the microstructure evolution of the plasticized PLLA during the hydrolytic degradation process was also investigated, and the results demonstrated the occurrence of PLLA crystallization, which was possibly contributed to the decreased hydrolytic degradation rate observed at relatively long hydrolytic degradation time. This work is of great significance and may open a new way for promoting the reclamation of PLLA waste material.     

Graphene oxide induced hydrolytic degradation behavior changes of poly(l-lactide) in different mediums

Graphene oxide (GO) has been widely used in polymer-based composites due to their promising properties originated from the two-dimensional platelet-like structure and a large number of oxygen-containing groups, including reinforcement effect, nucleation effect, barrier effect, etc. In this work, GO was introduced into poly(l-lactide) (PLLA) and the main attention was focused on investigating the effect of GO on hydrolytic degradation behavior of PLLA. The hydrolytic degradation measurements were carried out in three different mediums, including alkaline solution with a pH value of 12, acidic solution with the pH value of 2 and deionized water with the pH value of 7. It was demonstrated that in all mediums, the hydrolytic degradation of PLLA was greatly accelerated by adding GO and specifically, the more the GO in the composites, the more apparent the acceleration effect of the hydrolytic degradation was, furthermore, GO didn't change the hydrolytic degradation mechanisms of the PLLA matrix in all mediums. The microstructure evolution of the PLLA matrix during the hydrolytic degradation process was also comparatively investigated. The results demonstrated that crystallization occurred during the hydrolytic degradation process and the crystallization of the composites was also greatly promoted by GO. This work provides valuable information for the application and reclamation of the PLLA/GO composites.     

Effects of molecular weight and small amounts of d-lactide units on hydrolytic degradation of poly(l-lactic acid)s

Films of poly(l-lactic acid) (PLLA) with different number-average molecular weights (M_n) and d-lactide unit contents (X_d) were made amorphous and the effects of molecular weight and small amounts of d-lactide units on the hydrolytic degradation behavior in phosphate-buffered solution at 37 °C of PLLA were investigated. The degraded films were investigated using gravimetry, gel permeation chromatography, polarimetry, differential scanning calorimetry, X-ray diffractometry, and tensile testing. To exclude the effects of crystallinity on the hydrolytic degradation, the films were made amorphous by melt-quenching. The incorporation of small amounts of d-lactide units drastically enhanced the hydrolytic degradation of PLLA. In the period of 0-32 weeks, the hydrolytic degradation rate constant (k) of PLLA films increased with increasing X_d, while the k values did not depend on M_n. This means that the effects of X_d on the hydrolytic degradation rate of the films are higher than those of M_n. In contrast, in the period of 32-60 weeks neither X_d nor M_n was a crucial parameter to determine k values, probably because in addition to these parameters the differences in the amount of catalytic oligomers accumulated in films and crystallinity affect the hydrolytic degradation behavior of the films. The initially amorphous PLLA films remained amorphous even after the hydrolytic degradation for 60 weeks.     

Biodegradable polyester/modified mesoporous silica composites for effective bone repair with self‐reinforced properties

A series novel composites based on poly(_L‐lactide) (PLLA) oligomer modified mesoporous silica (MCM41) homogeneous dispersed into poly(_L‐lactide‐co‐trimethylene carbonate‐co‐glycolide) (PLTG) terpolymer has been successfully prepared. The structure of PLTG terpolymer was characterized by ¹H NMR. The structure and properties of modified and unmodified MCM41 were attested by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyzer (TGA), X‐ray diffraction (XRD), N₂ adsorption–desorption, scanning electron microscope (SEM), and transmission electron microscope (TEM), which demonstrated that the MCM41 was successfully grafted by the PLLA oligomer. The effect of different concentration of modified MCM41 in PLTG matrix on thermal properties, mechanical properties, and hydrophilicity was investigated by TGA, differential scanning calorimetry (DSC), mechanical testing, contact angle measurement, and SEM. The results of mechanical tests showed that 5 wt% of modified MCM41 nanoparticles gave rise to optimal reinforcing effect. The tensile strength, Young's modulus, and elongation at break of the PLTG/PLLA‐MCM41 (5%) composites were 33.2 Mpa, 1.58 Gpa, and 268.7%, respectively, which were all higher than the PLTG/MCM41 (5%) composites and pristine PLTG matrix, which were due to good interfacial adhesion between the PLTG matrix and MCM41 nanoparticles. TGA and DSC have shown that 5% modified MCM41 in the PLTG increased the temperature of composite degradation and T_g. Water contact angle measurement showed the hydrophilicity of the composites increases with the increase of modified MCM41 content. The live/dead assay showed that the modified MCM41 existing on the PLTG matrix presents very excellent cytocompatibility. Therefore, the novel composite material represents promising way for bone tissue engineering application.     

Isothermal crystallization kinetics and melting behavior of PLLA/f-MWNTs composites

Poly(l-lactide) (PLLA) and functionalized multi-walled carbon nanotubes (f-MWNTs) were used to prepare PLLA/f-MWNTs composites via solution blending. The structure and morphology of f-MWNTs were characterized using FT-IR and SEM. The spherulitic morphologies, isothermal crystallization kinetics, and melting behavior of the resulting PLLA/f-MWNTs composites were investigated by POM and DSC, respectively. Both Avrami and Lauritzen–Hoffman kinetics models are used to quantitatively evaluate the crystallization half-time t _1/2, the nucleation constant K _g, and the work of chain folding q of PLLA and its composites. Temperature modulated DSC was used to investigate the mechanism of overlapped endothermic and exothermic peaks of PLLA/f-MWNTs composites. The results indicated that the SiO₂ coating on the MWNTs could react with coupling agent KH-550 leading to the formation of f-MWNTs, which can be evenly dispersed in PLLA matrix. A decrease of spherulite size and an increase of crystallization rate were observed from POM measurements for PLLA/f-MWNTs. The multiple melting behavior can be attributed to the melt-recrystallization process of PLLA/f-MWNTs composites at certain temperature.     

Rheology and crystallization behavior of PLLA/TiO2‐g‐PDLA composites

Poly(L‐lactide) (PLLA) composites with TiO₂‐g‐poly(D‐lactide) (PDLA), which was synthesized by surface‐initiated opening ring polymerization with TiO₂ as initiator and Sn(Oct)₂ as catalyst, were prepared by solution casting. The synthesized TiO₂‐g‐PDLA was characterized by transmission electron microscope (TEM) and dynamic laser scattering (DLS), showing larger size corresponding to that of TiO₂. Fourier transform infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectroscopy (XPS) measurements were further carried out and indicated that PDLA was grafted onto TiO₂ through covalent bond. For PLLA/TiO₂‐g‐PDLA composites, the stereocomplex crystallites were formed between PDLA grafted on the surface of TiO₂ and the PLLA matrix, which was determined by FT‐IR, differential scanning calorimetry (DSC), and X‐ray diffractometer (XRD). The influence of stereocomplex crystallites on the rheological behavior of PLLA/TiO₂‐g‐PDLA was investigated by rheometer, which showed greater improvement of rheological properties compared to that of PLLA/TiO₂ composites especially with a percolation content of TiO₂‐g‐PDLA between 3 wt%–5 wt%. The crystallization and melting behavior of PLLA/TiO₂‐g‐PDLA composites were studied by DSC under different thermal treatment conditions. The formed PLA stereocomplex network acted as nucleating agents and a special interphase on the functional surface of TiO₂, which resulted in imperfect PLLA crystal with lower melting temperature. When the thermal treatment was close to the melting temperature of PLA stereocomplex, the crystallinity approached to the maximum. The isothermal crystallization study by polarizing microscope (POM) indicated that stereocomplex network presented stronger nucleation capacity than TiO₂‐g‐PDLA. Copyright © 2015 John Wiley & Sons, Ltd.     

Surface‐modified hydroxyapatite linked by L‐lactic acid oligomer in the absence of catalyst

A new surface modification method of hydroxyapatite nanoparticles (n‐HA) by surface grafting reaction of L ‐lactic acid oligomer with carboxyl terminal (LAc oligomer) in the absence of any catalyst was developed. The LAc oligomer with a certain molecular weight was directly synthesized by condensation of L ‐lactic acid. Surface‐modified HA nanoparticles (p‐HA) were attested by Fourier transformation infrared spectroscopy, ³¹P MAS‐NMR, and thermal gravimetric analysis (TGA). The results showed that LAc oligomer could be grafted onto the n‐HA surface by forming a Ca carboxylate bond. The grafting amount of LAc oligomer was about 13.3 wt %. The p‐HA/PLLA composites showed good mechanical properties and uniform microstructure. The tensile strength and modulus of the p‐HA/PLLA composite containing 15 wt % of p‐HA were 68.7 MPa and 2.1 GPa, respectively, while those of the n‐HA/PLLA composites were 43 MPa and 1.6 GPa, respectively. The p‐HA/PLLA composites had better thermal stability than n‐HA/PLLA composites and neat PLLA had, as determined by isothermal TGA. The hydrolytic degradation behavior of the composites in phosphate buffered saline (PBS, pH 7.4) was investigated. The p‐HA/PLLA composites lost their mechanical properties more slowly than did n‐HA/PLLA composites in PBS because of their reinforced adhesion between the HA filler and PLLA matrix. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5177–5185, 2005     

Accelerated hydrolytic degradation of Poly(l-lactide)/Poly(d-lactide) stereocomplex up to late stage

Poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) blend specimens containing only stereocomplex as crystalline species, together with those of pure PLLA and PDLA specimens, were prepared by solution crystallization using acetonitrile as the solvent. Their accelerated hydrolytic degradation was carried out in phosphate-buffered solution at elevated temperatures of 70-97 °C up to the late stage. During hydrolytic degradation, the stereocomplex crystalline residues were first traced by gel permeation chromatography. Similar to the hydrolytic degradation of pure PLLA and PDLA specimens, the hydrolytic degradation of stereocomplexed PLLA/PDLA blend specimens slowed down at the late stage when most of the amorphous chains were removed and crystalline resides were formed and degraded. The estimated activation energy for hydrolytic degradation of stereocomplex crystalline residues (97.3 kJ mol⁻¹) is significantly higher than 75.2 kJ mol⁻¹ reported for α-form of PLLA crystalline residues. This indicates that the stereocomplex crystalline residues showed the higher hydrolysis resistance compared to that of α-form of PLLA crystalline residues.     

Thermal and electrical properties of poly(l-lactide)-graft-multiwalled carbon nanotube composites

The dispersion of the nanometer-sized carbon nanotubes in a polymer matrix leads to a marked improvement in the properties of the polymer. This approach can also be applied to biodegradable synthetic aliphatic polyesters such as poly(l-lactide) (PLLA), which has received a great deal of attention due to environmental concerns. In this study, PLLA was melt compounded with multiwalled carbon nanotubes (MWCNTs). A high degree of dispersion of the MWCNTs in the composites was obtained by grafting PLLA onto the MWCNTs (PLLA-g-MWCNTs). After oxidizing the MWCNTs by treating them with strong acids, they were reacted with l-lactide to produce the PLLA-g-MWCNTs. The morphology of the composite was observed with scanning electron microscopy. The mechanical properties of the PLLA/PLLA-g-MWCNT composite were higher than those of the PLLA/MWCNT composite. The thermal stability of the composites was studied using thermogravimetric analysis and their activation energy during thermal degradation was determined using the Kissinger and Flynn-Wall-Ozawa methods. The activation energy of PLLA/PLLA-g-MWCNT was higher than that of PLLA/MWCNT, which indicates that the composite made with the PLLA-g-MWCNTs was more thermally stable than the composite made with the MWCNTs.     

PLLA Based Composites with α-Tricalcium Phosphate and a PLLA-PEO Diblock Copolymer

Hybrid composites consisting of poly(L -lactide), PLLA, or blends of PLLA with a PLLA-poly(ethylene oxide) diblock copolymer (15–30 wt%), COP, as a biodegradable polymeric matrix and of bioactive α-tricalcium phosphate, α-TCP, microparticles as dispersed phase (25–40 wt-%) were prepared by melt extrusion and their thermal, mechanical and degradation behaviour was investigated. SEM analysis of surfaces broken in liquid N₂ showed a good dispersion of α-TCP in the polymer matrix. A lowering of the glass transition temperature of the polymer matrix and enhanced crystallization rates of PLLA, both from the melt and from the glassy state, were observed in the presence of COP. Ternary PLLA/COP/α-TCP composites containing about 10 wt-% of COP and 25–40 wt-% of α-TCP showed improved compressive strength and deformation at yield as compared to pure PLLA. Degradation experiments revealed that in simulated body fluid the presence of α-TCP particles promoted the formation of inorganic deposits of a poor crystalline apatitic phase on composite surfaces as compact sferoids.     

Moisture and solvent responsive cellulose/SiO<Subscript>2</Subscript> nanocomposite materials

Water responsive SiO₂/cellulose nanocomposite hydrogels and films were constructed, for the first time, by dispersing SiO₂ nanoparticles into cellulose solution in LiOH/urea solvent, and then by crosslinking with epichlorohydrin or regeneration in coagulation bath, respectively. The cellulose nanocomposite materials were characterized by Field emission scanning electron microscopy, FTIR, dynamic rheology, wide angle X-ray diffraction and mechanical test. The SiO₂/cellulose nanocomposites at wet state or in water displayed unique behaviors, showing higher light transmittance than those before contacting with water. The results revealed that strong hydrogen-bonding interaction among water, cellulose and SiO₂ led the good dispersion of SiO₂ nanoparticles in the cellulose matrix. The incorporation of SiO₂ nanoparticles improved the transmittance and mechanical strength of the cellulose hydrogels, and also enhanced the mechanical strength of the films. Especially, the cellulose/SiO₂ nanocomposite films were milky at dry state, and changed to transparent after being soaked in water, different from the cellulose film without the SiO₂ nanoparticles. In our findings, SiO₂ and cellulose with water could form strong hydrogen bonding to create a homogenous network structure. The cellulose/SiO₂ composite as a smart material exhibited moisture and solvent responsiveness, showing potential applications in moisture detection.     

Synthesis and characterization of polyaniline/silicon dioxide composites and preparation of conductive films

The focus of this study was to synthesize the inherently conductive polymer polyaniline using an optimized process to prepare polyaniline/silicon dioxide (PANI/SiO₂) composites by in situ polymerization and ex situ solution mixing. PANI and PANI/SiO₂ composite films were prepared by drop‐by‐drop and spin coating methods. The electrical conductivities of HCl doped PANI film and PANI/SiO₂ composite films were measured according to the standard four‐point‐probe technique. The composite films exhibited an increase in electrical conductivity over neat PANI. PANI and PANI/SiO₂ composites were also investigated by spectroscopic methods including UV‐Vis, FT‐IR, and Photoluminescence. UV‐Vis and FT‐IR studies showed that SiO₂ particles affect the quinoid units along the polymer backbone and indicate strong interactions between the SiO₂ particles and the quinoidal sites of PANI (doping effect). The photoluminescence properties of PANI and PANI/SiO₂ composites were studied and the PANI/SiO₂ composites showed increased intensity as compared to neat PANI. The increase of conductivity of PANI/SiO₂ composite may be partially due to the doping or impurity effect of SiO₂ where the silicon dioxides compete with chloride ions. The morphology of particles and films were examined by a scanning electron microscope (SEM). SEM measurements indicated that the SiO₂ were well dispersed and isolated in composite films. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation and properties of polycarbonate/polyhedral oligomeric silsesquioxanes (POSS) hybrid composites

Octaphenylsilsesquioxane (PH‐POSS) and octa(γ‐methacryloxypropyl)silsesquioxane (MA‐POSS) were successfully synthesized by hydrolytic condensation of phenyltrichlorosilane and γ‐methacryloxypropyltrimethoxysilane, and characterized by Fourier transform infrared (FT‐IR), ¹H and ²⁹Si nuclear magnetic resonance (NMR), and matrix‐assisted laser desorption/ionization‐time of flight (MALDI‐TOF) mass spectrum. Morphology, degradation behavior, thermal, and mechanical properties of hybrid composites were studied by transmission electron microscopy (TEM), polarized optical microscopy (POM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), surface contact angle (SCA), tensile, and impact testing. Domains of PH‐POSS and MA‐POSS dispersed in the matrix with a wide size distribution in a range of 0.1–0.5 µm, while PH‐POSS exhibited a preferential dispersion. Because of the possible homopolymerization of MA‐POSS during the melt blending, the glass transition temperature of polycarbonate (PC)/MA‐POSS composites remained nearly unchanged with respect to PC/PH‐POSS composites that showed a depression of T_g due to the plasticization effect. It is interesting to note that the incorporation of POSS retarded the degradation rates of PC composites and thus significantly improved the thermal stabilities. Si? O fractions left during POSS degradations were a key factor governing the formation of a gel network layer on the exterior surface. This layer possessed more compact structures, higher thermal stabilities, and some thermal insulation. In addition, percentage residues at 700°C (C₇₀₀) significantly increased from 10.8% to 15.8–22.1% in air. Fracture stress of two composites showed a slight improvement, and the impact strength of them decreased monotonically with the increase of POSS loading. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrolytic degradation of polyisobutylene and poly‐L‐lactide–based multiblock copolymers

The hydrolytic degradation of a series of poly‐L ‐lactide (PLLA)‐polyisobutylene (PIB) multiblock copolymers was studied in phosphate buffer solution (pH = 7.4) at 37 °C. The multiblock copolymers were synthesized by chain extension of PLLA‐b‐PIB‐b‐PLLA triblock copolymers, which were obtained by ring‐opening polymerization of L ‐lactide initiated by hydroxyallyl telechelic PIB. The degradation strongly depended on the PLLA segment length. At constant PIB segment length, the multiblock copolymer with the shortest PLLA segment length (DPn = 10), showed significant weight loss after 8 weeks, whereas weight loss for DPn = 36 was only observed after 24 weeks. The gel‐permeation chromatographic analysis showed a similar decrease in the number‐average molecular weight (M_n) with time further supporting the weight loss data. Dynamic mechanical analysis showed a decrease in ultimate stress and modulus with time. The crystallinity of multiblock copolymers changed significantly with degradation time as indicated from differential scanning calorimetric analysis. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3767–3774, 2010     

Co-templating synthesis of highly dispersed 1D ZnO nanostructures in amorphous SiO2 under hydrothermal condition

One-dimensional (1D) ZnO nanostructures were grown in amorphous SiO₂ matrix by a co-templating method under hydrothermal condition. Using ethylenediamine (EDA) groups grafted mesoporous silica MCM-41 as a co-template, the growth of 1D ZnO nanostructures was oriented by soft EDA groups and confined inside the hard mesochannels of MCM-41. The microstructure and morphology of the 1D-ZnO-nanostructures/SiO₂ composite were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). All these results indicate that the 1D ZnO nanostructures were synthesized and highly dispersed in the amorphous SiO₂ matrix. Blue-shifted exciton absorption was observed from the co-templating synthesized sample.     

Nanocomposites of poly(l-lactide) and surface-grafted TiO2 nanoparticles: Synthesis and characterization

A new method of surface modification of TiO₂ nanoparticles by surface-grafting l-lactic acid oligomer was developed. The surface-grafting reaction was evaluated by Fourier transformation infrared (FTIR) and thermal gravimetric analysis (TGA). The results showed that l-lactic acid oligomer could be easily grafted onto the TiO₂ nanoparticles surface in the presence of stannous octanoate and the highest amount of grafted polymer was about 8.5% in weight. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) results showed that grafted TiO₂ (g-TiO₂) in chloroform or PLLA matrix approximated to uniform, while unmodified TiO₂ nanoparticles tended to aggregate. The tensile strength of this material was greatly improved by the addition of g-TiO₂ nanoparticles in poly(l-lactide) (PLLA) matrix. The tensile strength of the g-TiO₂/PLLA nanocomposite containing 5 wt.% of g-TiO₂ was 72 MPa, which was 23.1% higher than that of pure PLLA. Even though the incorporation of the TiO₂ nanoparticles into PLLA led to the deterioration of its elongation at break, the g-TiO₂/PLLA nanocomposite also exhibited better ductility than that of TiO₂/PLLA nanocomposite.     

Antibacteria and Detoxification Function of Polystyrene/TiO2 Nanocomposites

The composites of TiO₂ nanoparticles (anatase structure, average particle size 20–30 nm) as inorganic particle additive in the polystyrene (PS) were prepared by co‐rotating twin screw extruder. The structure and morphology of the composites were determined by scanning electron microscope (SEM), transmission electron microscopy (TEM) and x‐ray diffraction (XRD). Titanium (Ti) element distribution on the surface of PS/TiO₂ master batch was measured by energydispersive x‐ray microanalysis system. The mechanical properties such as tensile strength and Charpy impact strength were tested and revealed that reached the maximum value when the content of TiO₂ nanoparticles is at 1.0 wt%. The composites possess excellent antibacterial and detoxification effect on the familiar bacillus. The antibacteria efficiency of the composites is more than 99% and its detoxification efficiency on the bacterial endotoxin is more than 90%.     

接枝改性POSS对PLLA结晶行为的影响*

以二氯甲烷为溶剂,利用溶液共混法将三种聚笼形多面体倍半硅氧烷(POSS)分别与聚左旋乳酸(PLLA)进行共混,制备了不同POSS含量的单氨基POSS(POSS-NH₂)/PLLA、POSS接枝聚乙二醇(POSS-PEG)/PLLA和POSS接枝聚乳酸(POSS-g-PLLA)/PLLA复合材料。利用差示扫描量热仪(DSC)、热重分析仪(TGA)、偏光显微镜(POM) 分别对复合材料的本体结晶行为、热稳定性及结晶形貌和生长速率进行了观察。结果表明当加入不同质量分数(1 wt%, 5 wt%, 10 wt%)的POSS-PEG时,PLLA的结晶能力均得到改善,而POSS-NH2和POSS-g-PLLA仅在质量分数较低(1wt%)时对PLLA起成核剂的作用,具有较高质量分数时会阻碍PLLA分子链段的运动,从而限制其结晶。三种复合材料中仅POSS-PEG在一定程度上提高了PLLA的热稳定性,利用POM观察球晶生长过程发现POSS-PEG的加入提高了PLLA的球晶生长速率。     

Cellulose nanofibril-reinforced biodegradable polymer composites obtained via a Pickering emulsion approach

Preparation of cellulose nanofibril (CNF)-reinforced, biodegradable polymer composites is challenging in that it’s hard to achieve good dispersion of the hydrophilic cellulose fibers in a hydrophobic polymer matrix. In this work, we developed a surfactant-free and efficient process to prepare CNF-reinforced poly (lactic acid) (PLA) composites from an aqueous dichloromethane Pickering emulsion self-emulsified by CNFs. CNF/PLA composites of homogeneous dispersion were obtained upon evaporation of CH₂Cl₂, filtration, drying and hot-pressing. Differential scanning calorimetry measurement revealed an enhanced crystallization capacity of the CNF/PLA composites. Thermogravimetric analysis indicated an increase of onset degradation temperature. The composites displayed an enhanced storage modulus compared with neat PLA throughout the testing temperature range, and especially in the high-temperature region (>70 °C). Enhancements of the flexural modulus and strength were also achieved.