Influence of Bovine Bone Content on In Vitro Degradation of Poly-L-lactic Acid and Bovine Bone Composite Materials

In vitro degradation experiments of poly-L-lactic acid (PLLA) and bovine bone (BB) composites were carried out in a phosphate-buffered solution (PBS) at 37°C with a pH of 7.4. The influence of BB content on pH value of PBS, water uptake, molecular weights, molecular weight distributions, weight losses, mechanical strengths, and morphologies of PLLA/BB was investigated with degradation times. The results indicated that the presence of the BB modified the degradation of the PLLA matrix. The degradation rate of PLLA in the PLLA/BB composite was slower than the degradation rate of the sole PLLA material. Furthermore, the degradation rate of the composites became slower with the increasing content of BB in PLLA/BB composites.     

Influence of Amount of Sulfur on Mechanical,Dynamic, and Shape-Memory Properties of Trans-1,4-Polyisoprene

Influence of the amount of sulfur on cure characteristics, crystallization characteristics, static and dynamic mechanical properties and shape-memory property during a tensile-recovery cycle of trans-1,4-polyisoprene (TPI) vulcanizates was investigated. The results showed that the scorch delay time, optimum cure time, degree of crystallinity and mechanical properties decreased with the increasing of sulfur amount. Both the glass transition of the amorphous regions and the melting transition of the crystalline regions appeared in curves of modulus and loss factor via temperature. The modulus before melting decreased, the loss peak for glass transition became stronger and the melting peak became weaker with increase of sulfur content. The shape recovery of TPI vulcanizates increased while the shape fixity decreased with the increasing sulfur amount. For example, the shape fixity was less than 60% when the sulfur amount was 3.0 phr.     

Preparation and In Vitro Degradation Behavior of Poly(L-lactide-co-glycolide) by Direct-Melt Polycondensation

Poly(L-lactide-co-glycolide)(PLGA)copolymer (85/15) was prepared by direct-melt polycondensation instead of a ring-opening process. The polymer samples were hydrolyzed at 37°C in phosphate-buffered saline (PBS) for periods up to 10 weeks and the degradation behavior was characterized through weight average molecular mass change, mass loss, water uptake, and morphology. The results indicate that mass loss, weight average molecular mass, and water uptake of PLGA increase with increasing time; however, pH value of the PBS solution decreases. The degradation is heterogeneous—degradation in their central parts was faster than in the surface and regions due to the increased concentration of the acidic degradation products inside.     

Fabrication of Poly-l-lactide Biomaterials with High Mechanical Properties Using Fiber Oriented Pressing

A new technique of dilute solution spinning to obtain poly-l-lactide (PLLA) fiber was presented. PLLA materials were fabricated by using fiber oriented pressing and the effects of pressing pressure and temperature on the mechanical properties and weight average molecular mass of PLLA were investigated. Good oriented fibers with porous structure (0.1 ～ 1 μm) were obtained by a dilute solution spinning method. Bending and shearing strength of PLLA samples first increase and then decrease with the increase of pressing temperature and pressure. The bending strength, shearing strength, and bending modulus reach 238.8 ± 6.5 MPa, 127.5 ± 3.5 MPa and 3.25 ± 0.25 GPa, respectively, if the pressing temperature is 185°C and the pressure is 130 MPa. These values are greater than conventional pressing methods. In addition, the decrease in weight average molecular mass (19.5%) that results from using oriented pressing is lower than that seen (30.0%) by using the conventional pressing method.     

Effects of Beta Irradiation,Copolymers, and Blends on the Transformation Rate of Polybutene-1

The beta irradiation of polybutene-1 (PB-1) and its random copolymers with ethylene results in sample degradation without chain cross-linking. The crystal structures of both homopolymer and ethylene copolymers were phase I (I), except that for samples of short time irradiation, after melting, where phase II (II) was also present. The sample crystallinity decreased from 64% to a low of 45% in the irradiated samples for the condition used. The crystal size/perfection of the transformed I was slightly lower than that of parent II. The beta irradiation increased the transformation rate of II → I but to a lower extent than did the amount of ethylene in the copolymers. IR analysis confirmed that electron irradiation resulted in chain scission and a decrease of ?CH₂? and ?CH₃ groups. The mechanical properties decreased with increasing ethylene content and irradiation dose.     

Nanocomposites of poly(l-lactide) and surface modified magnesia nanoparticles: Fabrication, mechanical property and biodegradability

A novel nanocomposite based on biodegradable poly(l-lactide) (PLLA) was prepared by the incorporation of surface modified magnesia (g-MgO) nanoparticles using a solution casting method. The mechanical properties, biodegradable properties and protein adhesion behavior of the g-MgO/PLLA nanocomposites were investigated. Scanning electron microscopy (SEM) results showed that g-MgO nanoparticles could comparatively uniformly disperse in PLLA matrix. The addition of g-MgO nanoparticles to PLLA matrix improved the tensile strength and elastic modulus, whereas reduced the elongation at break. The mass loss results showed that the nanocomposites with higher g-MgO content had faster degradation rates. The in vitro pH value determination results indicated that the g-MgO nanoparticles could neutralize effectively the lactic acid resulting from the degradation of PLLA. The g-MgO/PLLA nanocomposites exhibited enhanced protein adsorption, i.e., with the increase of g-MgO content, the amount of protein adsorption increased. The (5 wt%)g-MgO/PLLA nanocomposites adsorbed 33% more protein than the pure PLLA.     

Fabrication of Poly(D,L-lactide-co-glycolide) Microspheres and Degradation Characteristics in vitro

Poly(D,L-lactide-co-glycolide) (PLGA, 75/25) microspheres were prepared by the emulsion solvent extraction/evaporation technique and their degradation behaviors in vitro at 37°C were investigated. PLGA microspheres with a smooth and nonporous surface were obtained, with a mean particle size of 114.15 μm. It was observed that mass loss and water uptake of PLGA increased with increasing degradation time; however, weight average molecular weight and the pH value of the phosphate buffered saline (PBS) solution decreased. The observed relative rates of mass loss vs. molecular weight decreases were consistent with the explanation that PLGA underwent bulk degradation rather than surface degradation. During the degradation time, the surface of the PLGA microspheres became coarse and there were many micropores that developed upon immersion in the PBS. The microspheres lost their spherical form with increasing degradation time.     

Preparation and Characterization of Gelatin–Poly(L-lactic) Acid/Poly(hydroxybutyrate-co-hydroxyvalerate) Composite Nanofibrous Scaffolds

Poly(L-lactic) acid (PLLA) scaffolds, prepared by electrospinning technology, have been suggested for use in tissue engineering. They remain a challenge for application in biological fields due to PLLA's slow degradation and hydrophobic nature. We describe PLLA, PLLA/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), and PLLA/PHBV/gelatin (Gt) composite nanofiberous scaffolds (Gt–PLLA/PHBV) electrospun by changing the electrospinning technology. The morphologies and hydrophilicity of these fibers were characterized by scanning electron microscopy (SEM) and water contact angle measurement. The results showed that the addition of PHBV and Gt resulted in a decrease in the diameters and their distribution and greatly improved the hydrophilicity. The in-vitro degradation test indicated that GT–PLLA/PHBV composite scaffolds exhibited a faster degradation rate than PLLA and PLLA/PHBV scaffolds. Dermal fibroblasts viabilities on nanofibrous scaffolds were characterized by [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide] (MTT) assay and cell morphologies after 7 days culture. Results indicated that the GT–PLLA/PHBV composite nanofibers showed the highest bioactivity among the three scaffolds and increased with increasing time. The SEM images of cells/scaffolds composite materials showed the GT–PLLA/PHBV composite nanofibers enhanced the dermal fibroblasts's adhesion, proliferation, and spreading. It is suggested that the nanofibrous composite scaffolds of GT–PLLA/PHBV composites would be a promising candidate for tissue engineering scaffolds.     

Preparation of Poly (L-lactic Acid) Microsphere

Poly (L-lactic acid) (PLLA) microspheres were prepared by a solvent evaporation method based on an oil/water emulsion. The effect of the mass ratio of PLLA and poly(vinyl alcohol) (PVA) on the formation of the microspheres was discussed, and the influence of extraction speed of dichloromethane on the microsphere morphology was also studied. Moreover, the influences of the PLLA concentration and the volume ratio of water phase to dichloromethane phase were investigated. The results showed that stable microspheres can be obtained under the conditions that the mass ratio of PLLA to PVA is 20:1. Porous microspheres were obtained under faster evaporating speed of dichloromethane. The microsphere size increased with increasing PLLA concentration. The microsphere size also increased with the increase of the volume ratio of water phase to dichloromethane phase.     

甲基苯基乙烯基硅橡胶电离总剂量效应

甲基苯基乙烯硅橡胶具有耐高低温、防震等独特优势,在航天器的减震、密封等领域具有广泛应用前景。研究了甲基苯基乙烯基硅橡胶的电离总剂量效应。结果表明,随着辐射剂量的增加,甲基苯基乙烯基硅橡胶的力学性能出现了不同程度的退化。拉伸强度和撕裂强度变化规律以1×106 Gy(Si)剂量点为分界点。低于该剂量,拉伸和撕裂随剂量增加快速下降;高于该剂量时,随辐照剂量增加,拉伸强度出现一定程度反弹,呈现出宽"U"形,而撕裂强度则是先增加后下降。拉断伸长率和邵氏硬度A随辐照剂量增加分别出现快速下降和增加,最终接近饱和。最后,从辐射交联和裂解方面讨论了甲基苯基乙烯基硅橡胶电离总剂量效应的潜在物理机制。     

The Effect of Peroxide Cross-Linking on the Properties of Low-Density Polyethylene

Low-density polyethylene (LDPE) was chemically cross-linked with various amounts of dicumyl peroxide (DCP). The cross-link density, determined by Flory–Rehner theory, showed an increase with increasing DCP. The gel content, densities of cross-linked LDPE, thermal stability, crystallization, melting behavior, and tensile properties were studied. The results showed a new finding about the change of weight loss after cross-linking; with increase in temperature, the weight loss showed an increase below the temperature of about 450°C and then showed a decrease at temperatures from about 450°C to 500°C after being cross-linked. The crystallinity, melting point, crystallization temperature, and elongation at break decreased with the increase in DCP. However, the maximum tensile stress increased with the increase in DCP, and the cross-linked samples showed a rubber-like behavior with no flow.     

Structural and ionic conductivity of PEO blend PEG solid polymer electrolyte

Structural and ionic conductivity of PEO blend PEG with KI solid polymer electrolyte system is presented. The polymer PEG showed miscible with the high molecular weight polymer PEO. The X-ray diffraction patterns of PEO/PEG with KI salt indicated the decrease in the degree of crystallinity with increasing concentration of the salt. The DSC measurements of PEO/PEG:KI polymer electrolyte system showed that the melting temperature is shifted towards the lower temperature with increase of the salt concentration. Optical micrographs demonstrated that the spherulites of different sizes are present along with dark regions between the spherulites for lower salt compositions. With increase of salt concentration more amorphous regions are observed. The significance of blend is the increase of one order in ionic conductivity when compared to without blend PEO electrolyte.     

Synergistic Effects of Polyethylene Glycol and Polyhedral Oligomeric Silsesquioxanes on Crystallization Behavior of Poly(L-lactide)

The synergistic effects of poly(ethylene glycol) (PEG) and polyhedral oligomeric silsesquioxanes (POSS) on the crystallization behavior of semicrystalline poly(L-lactide) (PLLA) were systemically investigated using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Initially, the influences of PEG and POSS, individually, on PLLA crystallization were studied. The results indicated that PEG, as an efficient plasticizer, enhanced the mobility of the PLLA chains, resulting in decreasing of the glass transition temperature. The enhanced crystallization capacity of PLLA was strongly dependent on the molecular weight and content of the PEG, increasing with decreasing of the molecular weight and increasing of the PEG content. The experimental results also indicated that POSS was a heterogeneous nucleating agent, promoting the crystallization of PLLA. The synergistic effects of PEG and POSS on PLLA crystallization were then analyzed. The results showed that in the presence of PEG and POSS the crystallinity of PLLA was further enhanced due to their synergistic effects.     

Synthesis of Co(II) Complex with Hexamethylenetetramine Using Jet Milling and Its Influence on the Thermal Performance of Poly(l-lactic acid)

Cobalt(II)-hexamethylenetetramine (Co(II)-HMTA) complex was prepared using jet milling. Elemental analysis and thermogravimetric analysis confirmed that the structure of the Co(II)-HMTA complex was Co(HMTA)₂Cl₂·6H₂O (LG). The influence of LG on the thermal performance of poly(l-lactic acid) (PLLA) was investigated. Isothermal crystallization behavior and X-ray diffraction analysis (XRD) results of PLLA/LG showed that LG could improve the crystallization performance of PLLA; 1% LG caused the half time of overall crystallization (t_1/2) of PLLA to decrease from 96.5 min to a minimum value 3.8 min at 100°C. However, the isothermal crystallization kinetics of PLLA/LG described using the Avrami equation and XRD analysis indicated that the isothermal crystallization temperature and the LG concentration significantly affected the isothermal crystallization process of PLLA. In particular, 0.3% LG caused the intensity of the X-ray crystal diffraction peaks of PLLA to decrease with an increase of isothermal crystallization time after increasing for the first 5 min. The thermal decomposition analysis of PLLA/LG showed that the onset decomposition temperature of PLLA with a small amount of LG was higher than that of the neat PLLA and PLLA with a high concentration LG.     

Mechanisms for regularization of chain folds during annealing of polyhexamethylene adipamide

The regular fold content of polyhexamethylene adipamide depends on the initial crystallization conditions, the degree of orientation, and the annealing time and temperature. At low annealing temperatures, the regular fold content increases linearly with crystallinity and arises from lamellar crystallization of isolated amorphous or interlamellar regions. At intermediate annealing temperatures, the increase in regular fold content greatly exceeds the crystallinity increase. The excessive increase in folds in this temperature range arises from regularization of loose loops and melting and recrystallization from extended to more folded type of crystals. At the higher annealing temperature, the crystallinity shows an increase relative to the fold content, and this implies that the increase in fold period occurs at the expense of folding.     

Preparation and Characterization of Poly(Vinyl Alcohol) (PVA)/SiO2, PVA/Sulfosuccinic Acid (SSA) and PVA/SiO2/SSA Membranes: A Comparative Study

Abstract

New organic–inorganic nanocomposites based on PVA, SiO₂ and SSA were prepared in a single step using a solution casting method, with the aim to improve the thermomechanical properties and ionic conductivity of PVA membranes. The structure, morphology, and properties of these membranes were characterized by Raman spectroscopy, small- and wide-angle X-ray scattering (SAXS/WAXS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), water uptake (Wu) measurements and ionic conductivity measurements. The SAXS/WAXS analysis showed that the silica deposited in the form of small nanoparticles (～ 10?nm) in the PVA composites and it also revealed an appreciable crystallinity of pristine PVA membrane and PVA/SiO₂ membranes (decreasing with increasing silica loading), and an amorphous structure of PVA/SSA and PVA/SSA/SiO₂ membranes with high SSA loadings. The thermal and mechanical stability of the nanocomposite membranes increased with the increasing silica loading, and silica also decreased the water uptake of membranes. As expected, the ionic conductivity increased with increasing content of the SSA crosslinker, which is a donor of the hydrophilic sulfonic groups. Some of the PVA/SSA/SiO₂ membranes had a good balance between stability in aqueous environment (water uptake), thermomechanical stability and ionic conductivity and could be potential candidates for proton exchange membranes (PEM) in fuel cells.     

X-ray diffraction study of temperature dependence of Nairit polychloroprene permolecular structure

With use of the X-ray technique the permolecular structure of Nairit polychloroprene has been investigated. It is shown that the relative degree of crystallinity decreases with the increase in the polymerization temperature. At relatively low temperatures (18–30°C), in Nairits intensive formation of nuclei occurs and simultaneously existing crystallites collapse. Although mean sizes of crystallites decrease, the degree of crystallinity increases. At higher temperatures (above 30°C) melting of existing crystallites and decrease in the number of nuclei lead to decrease in crystallinity and mean sizes of crystallites.     

Influence of Blend Composition on Crystallization of Poly(L-Lactic Acid)/Poly (Ethylene Oxide) Crystalline/Crystalline Blends

The effect of blend composition on crystallization morphology and behavior of a crystalline/crystalline blend, poly(l-lactic acid) (PLLA)/poly(ethylene oxide) (PEO), during slow, non-isothermal crystallization was studied by polarized light microscopy (PLM) connected with a hot-stage and differential scanning calorimetry (DSC). The results showed that all of the PLLA/PEO blends produced spherulites which gradually became bigger and looser, as well as coarser, with the increment of the PEO content, indicating that the PEO crystals was resided in the interlamellar or interfibrillar (between clusters of commonly oriented lamellae) regions of the PLLA spherulites. In the (25/75) and (10/90) blends, the nucleation and growth processes of the PEO spherulites could be clearly observed in the pre-existing PLLA spherulites. The onset crystallization temperature and the melting point of one component decreased with increasing the content of the other one owing to the good miscibility of the two components in the non-crystalline state and the interaction between their macromolecules, indicating that the crystallization of each component was influenced by the other one.     

Thermal Performance of a Blend System Based on Poly(l-lactic acid) and an Aliphatic Multiamide Derivative of 1H-Benzotriazole

An aliphatic multiamide derivative derived from 1H-benzotriazole, N, N'-bis(1H-benzotriazole) sebacic acid acethydrazide (SA), was synthesized to evaluate its effect on the thermal performance, including non-isothermal crystallization and melting behavior as well as thermal stability, of poly(l-lactic acid) (PLLA). The comparative study, by means of DSC measurements, showed that the incorporation of SA caused a non-isothermal crystallization peak to appear and become sharp, showing its advanced crystallization promoting effect for PLLA. The non-isothermal crystallization results further indicated that 2 wt% SA was the saturation concentration for PLLA crystallization, and that the cooling rate was also a crucial determinant for PLLA crystallization. Considering the melting behavior, the difference between the virgin PLLA and PLLA/2%SA further confirmed the crystallization accelerative effect of SA for PLLA, with the increase of crystallization temperature in the temperature zone from 90 to 130°C being beneficial to the crystallization of PLLA during processing. Compared to the virgin PLLA, the trends of thermal decomposition curves were similar, suggesting that the introduction of SA of 0.5–3 wt% did not significantly change the thermal decomposition behavior of PLLA.     

Effect of gamma irradiation on high temperature hardness of low-density polyethylene

Gamma irradiation can cause the change of microstructure and molecular structure of polymer, resulting in the change of mechanical properties of polymers. Using the hardness measurement, the effect of gamma irradiation on the high temperature hardness of low-density polyethylene (LDPE) was investigated. The gamma irradiation caused the increase in the melting point, the enthalpy of fusion, and the portion of crystallinity of LDPE. The Vickers hardness of the irradiated LDPE increases with increasing the irradiation dose, annealing temperature, and annealing time. The activation energy for the rate process controlling the reaction between defects linearly decreases with the irradiation dose. The process controlling the hardness evolution in LDPE is endothermic because LDPE is semi-crystalline.