Poly(lactic acid)/(styrene‐ethylene‐butylene‐styrene)‐g‐maleic anhydride copolymer/sepiolite nanocomposites: Investigation of thermo‐mechanical and morphological properties

In this study, sepiolite nanoclay is used as reinforcing agent for poly(lactic acid) (PLA)/(styrene‐ethylene‐butylene‐styrene)‐g‐maleic anhydride copolymer (SEBS‐g‐MA) 90/10 (w/w) blend. Effects of sepiolite on thermal behavior, morphology, and thermomechanical properties of PLA/SEBS‐g‐MA blend were investigated. Differential scanning calorimetry results showed 7% improvement in crystallinity at 0.5 wt% of sepiolite. The nanocomposite exhibited approximately 36% increase in the tensile modulus and 17% increase in toughness as compared with the blend matrix at 0.5 and 2.5 wt% of sepiolite respectively. Field emission scanning electron microscopy and transmission electron microscopy images exhibited sepiolite‐induced morphological changes and dispersion of sepiolite in both PLA and SEBS‐g‐MA phases. Dynamic mechanical analysis and wide angle X‐ray diffraction present evidences in support of the reinforcing nature of sepiolite and phase interaction between the filler and the matrix. This study confirms that sepiolite can improve tensile modulus and toughness of PLA/SEBS‐g‐MA blend.     

Properties of acrylonitrile butadiene rubber (NBR)/poly(lactic acid) (PLA) blends and their foams

Abstract

Thermoplastic elastomers and their foams were prepared by blending elastomeric acrylonitrile butadiene rubber (NBR) and rigid poly(lactic acid) (PLA) with various PLA compositions ranging between 0 and 40%. The thermal and mechanical properties and the morphologies of the blends with various PLA contents were investigated through universal testing machine, differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscope analysis. The rheological properties during gel formation were in situ monitored through the evolution of torque with curing time. Furthermore, the microcellular structures and physical properties of the NBR/PLA foams prepared using organic blowing agents were studied. The NBR/PLA blends showed a two-phase morphology made of a continuous NBR matrix and micron or submicron nodules and the tensile strength and modulus; also, hardness of the NBR/PLA blends increased with the increase of the added PLA content. While the foamed samples exhibited a similar cell structure and foaming ratio to that of the pure NBR, the cell formation was considerably reduced as the added PLA content exceeded 30%. We conclude that the mechanical properties of NBR thermoplastic elastomer as well as its foams can be controlled by a judicious introduction of rigid and biodegradable PLA.     

Surface functionalized waste-silk fabric engineered with polylactic acid & activated charcoal for oil/solvent recovery from oily wastewater

The present study reports using waste silk fabric functionalized using Polylactic acid (PLA) and Activated charcoal for oil/solvent recovery from simulated seawater (3.5% NaCl-based water). An average of 91% separation was visible in the functionalized waste silk fabric with an efficiency up to 20 cycles towards petroleum oils/solvents from simulated seawater. Further, the functionalized waste fabric showed hydrophobic properties with a water-based contact angle of 105° and oil/solvent absorption towards petroleum oils and organic solvent, with a surface free energy of 52.46 mN m⁻¹. The functionalized waste silk also showed permeation flux of 658, 386, and 993 L m⁻² h⁻¹, for Petrol, Diesel, and n-Hexane, respectively. The results show that PLA/Activated-charcoal engineered waste silk can be effectively applied for practical oil/solvent recovery from simulated seawater. Utilizing waste silk fabric further supports in reducing the global carbon footprints as silk does not emit and/-or produce carbon dioxide due to its green origin and generating the circular economy approach.     

In vitro degradation and release profiles for electrospun polymeric fibers containing paracetanol

In the paper, the poly(D,L-lactide) (PDLLA) and poly(ethylene glycol)-co-poly(D,L-lactide) (PELA) fibers with and without paracetanol drug loading were prepared with an electrospinning method. The morphology of the fibers was observed by scanning electronic microscope (SEM). Their glass transition temperatures (T(g)) were measured with differential scanning calorimetry (DSC). The water contact angle (CA) measurement was also performed to characterize surface properties of fibers. At 37 degrees C in a PBS buffer solution (pH 7.4), in vitro matrix degradation profiles of these fibers were characterized by measuring their weight loss, the molecular weight decrease, and their morphology change. The result showed that the effects of fiber diameter and porosities on the degradation of the electrospun scaffolds might exceed the effects of the molecular weight and the PEG contents, which was different from the polymeric microspheres degradation. In vitro paracetanol release profiles were also investigated in the same condition. The result showed that the drug burst release behaviour was mainly related with the drug-polymer compatibility and the followed sustained release phase depended on polymer degradation.     

Current advances in microbial cell factories for lactate-based polyesters driven by lactate-polymerizing enzymes: Towards the further creation of new LA-based polyesters

Polylactic acid (PLA), a representative bio-based polyester, has been commonly synthesized via a multi-step by chemical process. The current modes of generating PLA involve microbial fermentation of starting material, lactic acid (LA), followed by chemical ring-opening polymerization. Recently, one-pot complete bioprocess for LA-based polyesters has been established as a microbial cell factory (MCF). The concept is a process conversion from the usual chemical factory to the MCF. This new challenge was triggered by discovery of an engineered LA-polymerizing enzyme (LPE). The LPE was found as one of the members of an extensive mutant library that has been created through the long-term evolutionary engineering study of natural biopolyester-synthesizing enzymes. Needless to say, a strategic method of getting the beneficial mutation in the enzyme is of the utmost importance and an essential step towards accomplishing the desired purpose, the acquisition of the LA-polymerizing activity in this case. In this review, the structures and properties of LPE-catalyzed polymerization products will be discussed as well as backgrounds on establishment of the MCFs for synthesis of LA-based polyesters. Also, experimental strategies for enrichment of the LA fraction will be proposed to further advance the prototype of MCF based on the related metabolic pathways.     

Effect of Drawing Temperature on Structure and Properties of a＇-Phase of Poly（lactic acid）

a＇-晶型聚乳酸（PLA）膜被制备和单轴拉伸．通过凝胶渗透色谱仪（GPC）、全反射红外光谱（ATR-IR）、差示扫描量热仪（DSC）,X射线衍射（XRD）及Raman光谱等测试技术研究了拉伸温度梯度变化对a＇-晶型PLA膜的分子量及其分布、分子链构象、结晶度、晶型转变和取向行为的影响．在恒定拉伸速度与应变下,拉伸温度对PLA膜的应力．应变曲线,特别是屈服强度、拉伸模量产生了较大的影响,其值随拉伸温度的增加而降低．GPC测试结果表明,在不同的温度下拉伸后,PLA会发生一定程度的降解,分子量降低;ATR-IR,XRD,DSC和Raman光谱测试结果表明,在不同的温度下拉伸后a’-型PLA没有发生晶型的转变,即没有由a＇-晶体转变为a-或β-晶体．结果表明PLA的结晶度、分子链取向程度强烈依赖于拉伸温度：当拉伸温度低于100℃时,a’-型PLA膜 的结晶度与沿着拉伸方向的变形程度随拉伸温度的增加而增加,分子链的高度取向诱导了PLA结晶;当拉伸温度超过100℃后,PLA的分子链沿着拉伸方向上的有序度与结晶度将降低．     

PLA/PBS/DCP反应共混体系的结晶行为研究

通过熔融共混法制备了一系列聚乳酸(PLA)/聚丁二酸丁二醇酯(PBS)物理共混试样及PLA/PBS/过氧化二异丙苯(DCP)反应共混试样,采用示差扫描量热分析(DSC)法研究了物理共混试样结晶行为及反应共混试样的特殊结晶行为.结果发现,PLA与PBS的物理共混并未改善PLA的结晶性,而PLA/PBS/DCP反应共混时生成的交联/支化结构可起到异相成核作用,从而明显改善了反应共混体系的结晶性能,且随着DCP含量的增加,共混体系中两相结晶行为出现交替变化.     

采用固体NMR研究MPEG-PLA双嵌段共聚物的固态相区结构

采用固体核磁共振方法，研究了AB型聚（L-丙氨酸）聚乙二醇嵌段共聚物(MPEG-b-PLA）的固态微相结构. ¹³C核的交叉极化与直接极化实验表明，MPEG中存在晶态和非晶态两种相区结构，PLA则含有大量的α螺旋与少量的β折叠二级结构. 由交叉极化过程下的¹³C自旋-晶格弛豫时间(T₁)测定结果进一步表明，MPEG链段由于嵌段结构使结晶过程受抑制，结晶度明显下降. PLA链段以结晶态形式存在，并由于大量α螺旋和β折叠有序结构的存在, 链段非常刚性，运动严重受限，而β位甲基因为可以自由旋转，所以运动能力较α位次甲基和羰基强.     

微米级聚酯醚嵌段共聚物微球的制备及其蛋白包裹研究

聚酯 醚嵌段共聚物聚 Ｄ，Ｌ 乳酸 聚乙二醇（Ｐｏｌｙ ＤＬ ｌａｃｔｉｄｅ Ｐｏｌｙｅｔｈｙｌｅｎｅｇｌｙｃｏｌ，ＰＬＡ ＰＥＧ）采用本体聚合法在１８０℃及－９５×１０－２ＭＰａ条件下制得．光谱分析证实产物结构．采用乳液溶剂蒸发法制备ＰＬＡ ＰＥＧ微球，粒径＜５μｍ．以复合乳液技术包裹蛋白．差示扫描量热分析确证ＰＬＡ ＰＥＧ有效包裹蛋白．ＢＣＡ法检测微球蛋白含量．结果表明与均聚物ＰＬＡ比较，ＰＬＡ ＰＥＧ不仅改善了成球条件而且蛋白的包裹效率明显提高．     

The role of PEG on the stability in digestive fluids and in vivo fate of PEG-PLA nanoparticles following oral administration

The aim of the present work was to evaluate if the presence of a polyethylenglycol (PEG) coating around PLA nanoparticles would affect their interaction with biological surfaces, following oral administration to rats. For this purpose, a model antigen, ¹²⁵I-radiolabeled tetanus toxoid, was encapsulated in PLA and PLA-PEG nanoparticles by a modified water-in-oil-in-water solvent evaporation technique. Firstly, the stability of the nanoparticles in simulated gastrointestinal fluids was evaluated. Results showed an interaction between the nanoparticles and the enzymes of the digestive fluids, this interaction being considerably reduced by the PEG coating around the particles. On the other hand, the PLA forming the nanoparticles was found to be only slightly degraded (9% converted to lactate for PLA nanoparticles and 3% for PLA-PEG nanoparticles) and that the encapsulated tetanus toxoid remained mostly associated to the nanoparticles upon incubation in the digestive fluids for up to 4 h. Finally, the in vivo experiments showed that, after oral administration to rats, the levels of encapsulated radioactive antigen in the blood stream and lymphatics were higher for PLA-PEG nanoparticles than for PLA nanoparticles. In conclusion, the PLA-PEG nanoparticles have a promising future as protein delivery systems for oral administration.