Our previous studies have shown that stereocomplexed hydrogels can be rapidly formed in vitro as well as in vivo upon mixing aqueous solutions of eight-arm poly(ethylene glycol)-poly(l-lactide) (PEG-PLLA) and poly(ethylene glycol)-poly(d-lactide) (PEG-PDLA) star block copolymers. In this study, stereocomplexation and photopolymerization are combined to yield rapidly in situ forming robust hydrogels. Two types of methacrylate-functionalized PEG-PLLA and PEG-PDLA star block copolymers, PEG-PLLA-MA and PEG-PDLA-MA, which have methacrylate groups at the PLA chain ends and PEG-MA/PLLA and PEG-MA/PDLA, which have methacrylate groups at the PEG chain ends, were designed and prepared. Results showed that stereocomplexed hydrogels could be rapidly formed (within 1-2 min) in a polymer concentration range of 12.5-17.5% (w/v), in which the methacrylate group hardly interfered with the stereocomplexation. When subsequently photopolymerized, these hydrogels showed largely increased storage moduli as compared to the corresponding hydrogels that were cross-linked by stereocomplexation or photopolymerization only. Interestingly, the storage modulus of stereocomplexed-photopolymerized PEG-PLA-MA hydrogels increased linearly with increasing stereocomplexation equilibration time prior to photopolymerization (from ca. 6 to 32 kPa), indicating that stereocomplexation aids in photopolymerization. Importantly, photopolymerization of stereocomplexed hydrogels could take place at very low initiator concentrations (0.003 wt %). Swelling/degradation studies showed that combining stereocomplexation and photopolymerization yielded hydrogels with prolonged degradation times as compared to corresponding hydrogels cross-linked by photopolymerization only (3 vs 1.5 weeks). Stereocomplexed-photopolymerized PEG-MA/PLA hydrogels degraded much slower than corresponding PEG-PLA-MA hydrogels, with degradation times ranging from 7 to more than 16 weeks. Therefore, combining stereocomplexation and photopolymerization is a novel approach to obtain rapidly in situ forming robust hydrogels. 相似文献
Aqueous solutions of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) form gels easily. The optimum condition of growth of the calcium tartrate crystal formed by diffusing calcium chloride into hydrogels containing tartaric acid was studied with use ofs- PVA of a syndiotacticity of 56 % and a degree of polymerization of 1460. The crystal grew in the gel of the concentrations of 2 % s-PVA and of 0.5 N tartaric acid at pH=4. The relation between the formation of Liesegang rings and shear modulus of a gel was studied by diffusing silver nitrate into gels containing potassium chromate. The distance between rings decreased with increasing shear modulus of a gel in the range from 670 to 7500 dyne/cm2. The Liesegang rings were not formed for the shear modulus gel for 280 and 16200 dyne/cm2. 相似文献
Nucleation capacity of organically modified natural montmorillonite within the surface-treated banana fiber (BF)-reinforced PLA biocomposites has been studied using DSC analysis in the present investigation. Both the surface treatments and nanoclays play vital roles in the variation in nucleation process of PLA during cold crystallization process. Biocomposite made up of silane-treated BF and its bionanocomposite prepared using cloisite 30B (C30B) were showed superior nucleation parameters, n and K values, in the Avrami plots. Enhanced equilibrium melting point and lower Ea suggests the reinforcing effect imparted by the BF surface treatments and C30B within the PLA matrix. Even though, Louritzen–Hoffmann theory was revealed that no change in crystallization regimes of PLA even after the biocomposite and bionanocomposite preparation. TG analysis revealed better heat barrier capacity for all the biocomposites and bionanocomposites in comparison with virgin PLA (V-PLA). Increased storage modulus values for biocomposites and bionanocomposites also confirm the reinforcing effects of the fillers. Heat deflection temperature and the flammability studies concluded better application window for newly developed materials than that V-PLA. 相似文献
Scaffolds based on biopolymers and nanomaterials with appropriate mechanical properties and high biocompatibility are desirable in tissue engineering. Therefore, polylactic acid (PLA) nanocomposites were prepared with ceramic nanobioglass (PLA/n-BGs) at 5 and 10 wt.%. Bioglass nanoparticles (n-BGs) were prepared using a sol–gel methodology with a size of ca. 24.87 ± 6.26 nm. In addition, they showed the ability to inhibit bacteria such as Escherichia coli (ATCC 11775), Vibrio parahaemolyticus (ATCC 17802), Staphylococcus aureus subsp. aureus (ATCC 55804), and Bacillus cereus (ATCC 13061) at concentrations of 20 w/v%. The analysis of the nanocomposite microstructures exhibited a heterogeneous sponge-like morphology. The mechanical properties showed that the addition of 5 wt.% n-BG increased the elastic modulus of PLA by ca. 91.3% (from 1.49 ± 0.44 to 2.85 ± 0.99 MPa) and influenced the resorption capacity, as shown by histological analyses in biomodels. The incorporation of n-BGs decreased the PLA crystallinity (from 7.1% to 4.98%) and increased the glass transition temperature (Tg) from 53 °C to 63 °C. In addition, the n-BGs increased the thermal stability due to the nanoparticle’s intercalation between the polymeric chains and the reduction in their movement. The histological implantation of the nanocomposites and the cell viability with HeLa cells higher than 80% demonstrated their biocompatibility character with a greater resorption capacity than PLA. These results show the potential of PLA/n-BGs nanocomposites for biomedical applications, especially for long healing processes such as bone tissue repair and avoiding microbial contamination. 相似文献
In this work, new ways of plasticizing polylactide (PLA) with low molecular poly(ethylene glycol) (PEG) were developed to improve the ductility of PLA while maintaining the plasticizer content at maximum 20 wt.% PLA. To this end, a reactive blending of anhydride-grafted PLA (MAG-PLA) copolymer with PEG, with chains terminated with hydroxyl groups, was performed. During the melt-processing, a fraction of PEG was grafted into the anhydride-functionalized PLA chains. The role of the grafted fraction was to improve the compatibility between PLA and PEG. Reactive extrusion and melt-blending of neat and modified PLA with PEG did not induce any dramatic drop of PLA molecular weight. The in situ reactive grafting of PEG into the modified PLA in PLA/PEG blends showed a clear effect on the thermal properties of PLA. It was demonstrated by DSC that the mobility gained by PLA chains in the plasticized blends yielded crystallization. The grafting of a fraction of PEG into PLA did not affect this process. However, DSC results obtained after the second heating showed an interesting effect on the Tg when 20 wt.% PEG were melt blended with neat PLA or 10 wt.% MAG-PLA. In the latter case, the Tg displayed by the reactive blend was shifted to even lower temperatures at around 14 °C, while the Tg of neat PLA and PLA blended with 20 wt.% PEG was around 60 and 23 °C, respectively. Regarding viscoelastic and viscoplastic properties, the presence of MAG-PLA does not significantly influence the behavior of plasticized PLA. Indeed, with or without MAG-PLA, elastic modulus and yield stress decrease, while ultimate strain increases with the addition of PEG into PLA. 相似文献
Preparing a polylactide (PLA)/plasticizer system has been regarded as an effective solution to improve the ductility of brittle PLA. In this reach, a novel type of alkyl phosphine oxides consisting of three aliphatic ester substituents was prepared from PH3 tail gas, and its potential to be employed as a PLA plasticizer was studied. Differential scanning calorimeter tests confirmed that the newly-prepared plasticizer decreased the Tg of PLA (28 wt% plasticizer) from 52°C (neat PLA) to 11°C, and increased the elongation at break from 11% (neat PLA) to 271% (plasticized PLA). X-ray diffraction results showed that the crystallization degree of PLA (28 wt% plasticizer) increased from 0.12% of neat PLA to 14.04%, while Young's modulus of PLA remained as high as 121.3 MPa, which was much higher than that of the PLA/citrate ester systems with same plasticizer content. These novel phosphorus-containing plasticizers exhibited excellent thermal stability and a weight-loss of the system no more than 2.5% at 180°C; therefore, no unpleasant volatiles were released during processing. In contrast, the weight loss of the PLA/citrate system was as high as 10.8% at 180°C, forming heavy fog with an unpleasant smell during thermal mixing. Scanning electron microscopy was employed to observe the microstructure of the PLA/plasticizer systems, which indicated that the carboxylic butyl ester-containing phosphine oxides was compatible with PLA matrix. 相似文献
The effect of cassava pulp (CP) on morphological, tensile, and thermal properties of a thermoplastic cassava starch (TPS)/poly (lactic acid) (PLA) blend was investigated. TPS/PLA/CP biocomposites were manufactured by melt extrusion and then converted into specimens using an injection molding. The weight fraction of PLA to TPS/CP was fixed at 40:60, whereas the final CP concentration in the composites was varied in the range of 4.4–22.1 wt%. CP could act as a reinforcement for TPS/PLA blend to enhance its tensile strength up to 354% and Young's modulus up to 722% when 22.1 wt% of CP was loaded and a nucleating agent for PLA as confirmed from the reduced Tcc. In addition, TPS/PLA/CP composites showed a discrete phase structure (i.e., droplets in matrix) when CP with lower concentration (i.e., 4.4 wt%, 8.8 wt%, and 13.3 wt%) was incorporated and a bicontinuous phase structure (i.e., co-continuous) when higher concentration of CP (i.e., 17.7 wt% and 22.1 wt%) was employed. The results suggest that TPS/PLA/CP biocomposites have potential to be used in the manufacturing of injection-molded articles, particularly when biodegradability and renewability of the material are required. 相似文献
We introduce a cationic polyamidoamine (PAMAM) dendrimers and tetronic (Te) based hydrogels in which precursor copolymers were prepared with simple methods. In the synthetic process, tyramine-conjugated tetronic (TTe) was prepared via activation of its four terminal hydroxyl groups by nitrophenyl chloroformate (NPC) and then substitution of tyramine (TA) into the activated product to obtain TTe. Cationic PAMAM dendrimers G3.0 functionalized with p-hydroxyphenyl acetic acid (HPA) by use of carbodiimide coupling agent (EDC) to obtain Den-HPA. 1H-NMR confirmed the amount of HPA and TA conjugations. The aqueous TTe and Den-HPA copolymer solution rapidly formed the cationic hydrogels in the presence of horseradish peroxidase enzyme (HRP) and hydrogen peroxide (H2O2) at physiological conditions. The gelation time of the hydrogels could be modulated ranging from 7 to 73 secs, when the concentrations of HRP and H2O2 varied. The hydrogels exhibited minimal swelling degree and low degradation under physical condition. In vitro cytotoxicity study indicated that the hydrogels were highly cytocompatible as prepared at 0.15 mg/mL HRP and 0.063 wt% of H2O2 concentration. Heparin release profiles show that the cationic hydrogels can sustainably release the anionic anticoagulant drug. The obtained results demonstrated a great potential of the cationic hydrogels for coating medical devices or delivering anionic drugs. 相似文献
This study evaluates the effects of nucleants phenylphosphonic acid zinc (PPA-Zn) and talc, mold temperature, and microfibrillated
cellulose (MFC) reinforcement in the acceleration of injection molding cycle of polylactic acid (PLA). PLA was dissolved in
an organic solvent, mixed with nucleant and MFC, and dried compounds were injection molded into molds at temperatures ranging
from 40 °C to 95 °C and holding times from 10 s to 120 s. Our results showed that PPA-Zn is more effective nucleating agent
compared to talc. The addition of 1 wt% PPA-Zn and the mold temperature of 95 °C exhibited the fastest crystallization rates
for the molded PLA, however, at this temperature the parts could not be quickly ejected without distortion. Addition of 10 wt%
MFC increased the stiffness of PLA at high temperatures and allowed ejection of parts without distortion at a holding time
of just 10 s. At this holding time, the crystallinity of the PLA composite was 15.3% but the storage modulus above Tg was superior to that of fully crystallized neat PLA due to MFC reinforcement, retaining the shape of the molded part during
demolding. The mechanical properties of the composite at room temperature were also higher than those of fully crystallized
neat PLA. 相似文献
Two novel biodegradable copolymers, including poly(ethylene glycol)-succinate copolymer (PES) and poly(ethylene glycol)-succinate-l-lactide copolymer (PESL), have been successfully synthesized via melt polycondensation using SnCl2 as a catalyst. The copolymers were used to toughen PLA by melt blending. The DSC and SEM results indicated that the two copolymers were compatible well with PLA, and the compatibility of PESL was superior to that of PES. The results of tensile testing showed that the extensibility of PLA was largely improved by blending with PES or PESL. At same blending ratios, the elongation at break of PLA/PESL blends was far higher than that of PLA/PES ones. The elongation maintained stable through aging for 3 months. The moisture absorption of the blends enhanced due to the strong moisture absorption of PEG segments in PES or PESL molecules, which did not directly lead to enhance the hydrolytic degradation rate of the PLA. The PLA blends containing 20–30 wt% PES or PESL were high transparent materials with high light scattering. The toughening PLA materials could potentially be used as a soft biodegradable packaging material or a special optical material. 相似文献
In the perspective of producing a rigid renewable and environmentally friendly rigid packaging material, two comb-like copolymers of cellulose acetate (AC) and oligo(lactic acid) OLA, feeding different percentages of oligo(lactic acid) segments, were prepared by chemical synthesis in solvent or reactive extrusion in the melt, using a diepoxide as the coupling agent and were used as compatibilizers for poly(lactic acid)/plasticized cellulose acetate PLA/pAC blends. The blends were extruded at 230 °C or 197 °C and a similar compatibilizing behavior was observed for the different compatibilizers. The compatibilizer C1 containing 80 wt% of AC and 14 wt% of OLA resulted effective in compatibilization and it was easily obtained by reactive extrusion. Considering these results, different PLAX/pAC(100-X) compounds containing C1 as the compatibilizer were prepared by extrusion at 197 °C and tested in terms of their tensile and impact properties. Reference materials were the uncompatibilized corresponding blend (PLAX/pAC(100-X)) and the blend of PLA, at the same wt%, with C1. Significant increase in Young’s modulus and tensile strength were observed in the compatibilized blends, in dependence of their morphologic features, suggesting the achievement of an improved interfacial adhesion thanks to the occurred compatibilization. 相似文献
A new class of polylactic acid (PLA)/polyethylene glycol (PEG) copolymer reinforced with bacterial cellulose nanofibers (BC) was prepared using a solvent casting and particulate leaching methods. Four weight fractions of BC (1, 2.5, 5, and 10 wt%) were incorporated into copolymer via silane coupling agent. Mechanical properties were evaluated using response surface method (RSM) to optimize the impact of pore size, porosity, and BC contents. Compressive strength obtained for PLA/PEG-5 BC wt% was 9.8 MPa, which significantly dropped after developing a porous structure to 4.9 MPa. Nielson model was applied to investigate the BC stress concentration on the PLA/PEG. Likewise, krenche and Hapli-Tasi model were employed to investigate the BC nanofiber reinforcement and BC orientation into PLA/PEG chains. The optimal parameters of the experiment results found to be 5 wt% for BC, 230 μm for pore size, and 80% for porosity. Scanning electron microscopy (SEM) micrograph indicates that uniform pore size and regular pore shape were achieved after an addition of BC-5% into PLA/PEG. The weight loss of copolymer-BC with scaffolds enhanced to the double values, compared with PLA/PEG-BC % without scaffolds. Differential Scanning Calorimetric (DSC) results revealed that the BC nanofiber improved glass transition temperature (Tg) 57 °C, melting temperature (Tm) 171 °C, and crystallinity (χ %) 43% of PLA/PEG reinforced-BC-5%. 相似文献
30 wt% aligned untreated long hemp fibre/PLA (AUL) and aligned alkali treated long hemp fibre/PLA (AAL) composites were produced by film stacking and subjected to accelerated ageing. Accelerated ageing was carried out using UV irradiation and water spray at 50 °C for four different time intervals (250, 500, 750 and 1000 h). After accelerated ageing, tensile strength (TS), flexural strength, Young's modulus (YM), flexural modulus and mode I fracture toughness (KIc) were found to decrease and impact strength (IS) was found to increase for both AUL and AAL composites. AUL composites had greatest overall reduction in mechanical properties than that for AAL composites upon exposure to accelerated ageing environment. FTIR analysis and crystallinity contents of the accelerated aged composites support the results of the deterioration of mechanical properties upon exposure to accelerated ageing environment. 相似文献
In order to improve the properties of wood flour (WF)/poly(lactic acid) (PLA) 3D-printed composites, WF was treated with a silane coupling agent (KH550) and acetic anhydride (Ac2O), respectively. The effects of WF modification and the addition of acrylicester resin (ACR) as a toughening agent on the flowability of WF/PLA composite filament and the mechanical, thermal, dynamic mechanical thermal and water absorption properties of fused deposition modeling (FDM) 3D-printed WF/PLA specimens were investigated. The results indicated that the melt index (MI) of the specimens decreased after WF pretreatment or the addition of ACR, while the die swell ratio increased; KH550-modified WF/PLA had greater tensile strength, tensile modulus and impact strength, while Ac2O-modified WF/PLA had greater tensile modulus, flexural strength, flexural modulus and impact strength than unmodified WF/PLA; after the addition of ACR, all the strengths and moduli of WF/PLA could be improved; after WF pretreatment or the addition of ACR, the thermal decomposition temperature, storage modulus and glass transition temperature of WF/PLA were all increased, and water absorption was reduced. 相似文献
A direct, efficient, and scalable method to prepare stereocomplexed polylactide (PLA)‐based nanoparticles (NPs) is achieved. By an appropriate combination of fabrication parameters, NPs with controlled shape and crystalline morphology are obtained and even pure PLA stereocomplexes (PLASC) are successfully prepared using the spray‐drying technology. The formed particles of varying d ‐ and l ‐LA content have an average size of ≈400 nm, where the smallest size is obtained for PLA50, which has an equimolar composition of PLLA and PDLA in solution. Raman spectra of the particles show the typical shifts for PLASC in PLA50, and thermal analysis indicates the presence of pure stereocomplexation, with only one melting peak at 226 °C. Topographic images of the particles exhibit a single phase with different surface roughness in correlation with the thermal analysis. A high yield of spherically shaped particles is obtained. The results clearly provide a proficient method for achieving PLASC NPs that are expected to function as renewable materials in PLA‐based nanocomposites and potentially as more stable drug delivery carriers.