四臂聚乳酸/线性聚乳酸共混物的结晶行为及机理研究

为了探究四臂聚乳酸对线性聚乳酸结晶行为的影响,将四臂聚乳酸与线性聚乳酸的共混物在示差扫描量热仪(DSC)和偏振光显微镜(PLM)热台中加热到熔点附近的不同温度下恒温后分别进行了降温—升温程序,考察了四臂聚乳酸对线性聚乳酸的结晶行为的影响.结果表明,随着四臂聚乳酸含量增加,四臂聚乳酸在共混物形成的晶体中的比例增大且四臂聚乳酸有促进共混物晶体完善的作用,导致了熔融过程中熔点的上升.进一步研究证明,在共混物中完全熔融的四臂聚乳酸的支化结构能够促进结晶成核点的形成,从而促进四臂聚乳酸/线性聚乳酸共混物的结晶;而部分熔融的四臂聚乳酸能大幅促进共混物的结晶能力,这是未完全熔融的晶体的成核作用所导致的.     

聚氧化乙烯-聚苯乙烯-聚氧化乙烯三嵌段共聚物/聚苯醚共混物的相容性和结晶行为

本工作对聚氧化乙烯-聚苯乙烯-聚氧化乙烯(PEO-PS-PEO)三嵌段共聚物与聚苯醚(PPO)均聚物共混物的相容性及结晶行为进行了研究。结果表明,共混体系的相容性与嵌段共聚物中苯乙烯段的含量有关,PS含量越高,PPO与共聚物PS段的相容性越好。共混体系的结晶行为也明显不同于一般均聚物共混体系。在DSC降温结晶过程中最多可出现三个结晶峰。     

聚氧化乙烯-聚苯乙烯-聚氧化乙烯三嵌段共聚物/聚苯醚共混物的相容性和结晶行为

 本工作对聚氧化乙烯-聚苯乙烯-聚氧化乙烯(PEO-PS-PEO)三嵌段共聚物与聚苯醚(PPO)均聚物共混物的相容性及结晶行为进行了研究。结果表明,共混体系的相容性与嵌段共聚物中苯乙烯段的含量有关,PS含量越高,PPO与共聚物PS段的相容性越好。共混体系的结晶行为也明显不同于一般均聚物共混体系。在DSC降温结晶过程中最多可出现三个结晶峰。     

聚β-羟基丁酸酯/聚氧化乙烯共混体系力学性能研究

本文详细研究了可完全生物降解的聚 β 羟基丁酸酯 (PHB)与水溶性聚氧化乙烯 (PEO)两元共混体系的拉伸力学性能 .讨论了PEO分子量、共混组成及热处理条件对共混体系力学性能的影响 .其中 ,PHB与超高分子量PEO(重均分子量 5× 10 6)共混 ,两组分力学上具有相容性 ,共混物的拉伸强度、断裂伸长率及模量都有明显的正的协同效应 .共混改性效果显著PHB的力学性能得到很大改善 ,尤其PHB的脆性缺陷 .并且 ,共混物在经过适当温度退火处理之后 ,共混物性能还可进一步改善     

聚左旋乳酸/聚氧化乙烯共混物的拉伸行为及结构转变

采用熔融共混方法制备了聚左旋乳酸(PLLA)和超高分子量聚氧化乙烯(PEO)共混物, 通过差示扫描量热(DSC)、 扫描电子显微镜(SEM)和二维广角X射线散射(2D-WAXS)等方法系统研究了PEO的加入对不同温度下PLLA拉伸行为及拉伸过程中微观结构变化的影响. 结果表明, PLLA/PEO共混物为非均相体系, PEO粒子均匀分布在PLLA中形成两相结构. PEO的加入能够显著降低PLLA的玻璃化转变温度(T_g), 在25～60 ℃范围内显著提高PLLA的拉伸性能. 在60 ℃拉伸时, PEO的加入提高了PLLA在拉伸过程中的结晶和形变能力. 在80 ℃拉伸时, 共混物的拉伸断裂伸长率下降, 但共混物的结晶速度仍高于纯PLLA样品.     

PLLA/PDLA立构复合晶体的结晶、熔融行为

以水为引发剂合成了两种构型不同的左旋聚乳酸和右旋聚乳酸,运用DSC研究了分子量较低的PLLA/PDLA立构复合聚乳酸晶体的多重熔融行为,观察到随着180℃等温时间的增加,PLLA/PDLA共混物的立构复合晶体的熔点和熔融峰面积呈现震荡性变化行为,进一步的DSC和在线X射线研究结果显示,聚乳酸立构复合晶体多重熔融峰的震荡行为来自于晶体中就近生长的过量异构体链段的调整过程。     

微量PEO-PS-PEO/PEO共混体系结晶过程中共聚物胶束的成核作用

本工作将Leibler等近期关于含非晶两嵌段共聚物“稀固体溶液”的胶束理论推广并应用到含结晶三嵌段共聚物的“稀固体溶液”.对微量聚氧化乙烯-聚苯乙烯-聚氧化乙烯三嵌段共聚物/聚氧化乙烯均聚物共混体系的结晶行为进行了研究.结果表明,共聚物胶束在共混体系的结晶过程中可以起到成核剂的作用.这对改善结晶均聚物的性能具有一定的应用价值.     

PEO／PVP共混体系结晶行为

本文用WAXD、PLM、DSC方法研究了聚氧化乙烯(PEO)/聚乙烯基吡咯烷酮(PVP)共混体系的结晶行为,探索了两组分聚合物间相互作用及体系结晶度与非晶组分含量的关系。DSC研究表明PEO/PVP共混体系具有两个玻璃化转变温度,分别是纯组分的T_g,无相容性。应用Avrami和LH方程对其动力学参数进行了研究。偏光显微镜观察了共混物结构形态。     

微量PEO-PS-PEO/PEO共混体系结晶过程中共聚物胶束的成核作用

 本工作将Leibler等近期关于含非晶两嵌段共聚物“稀固体溶液”的胶束理论推广并应用到含结晶三嵌段共聚物的“稀固体溶液”.对微量聚氧化乙烯-聚苯乙烯-聚氧化乙烯三嵌段共聚物/聚氧化乙烯均聚物共混体系的结晶行为进行了研究.结果表明,共聚物胶束在共混体系的结晶过程中可以起到成核剂的作用.这对改善结晶均聚物的性能具有一定的应用价值.     

聚乳酸/羧基化聚丙烯共混物的形态与热性能研究

以扫描电子显微镜、热重分析仪、差示扫描量热仪、热台偏光显微镜分别研究了聚乳酸/羧基化聚丙烯共混体系的相形态、热性能和结晶形态.结果显示,共混物熔体冷却时,聚乳酸和羧基化聚丙烯均形成球晶,但羧基化聚丙烯球晶较大而十字消光较暗,聚乳酸球晶尺寸较小而十字消光较亮,且聚乳酸球晶产生规则的、不连续的同心环线——裂纹,裂纹厚度约为1~2μm,且裂纹内部有微纤存在.当聚乳酸含量≤50%时,由于聚丙烯上羧基的存在而使共混体系具有较好的相容性.共混物的热分解过程分为三个阶段,热分解温度的变化是聚丙烯上的羧基、聚乳酸和聚丙烯骨架分解三种机制共同作用的结果,少量聚乳酸能够明显提高共混物中聚丙烯上羧基的热稳定性.共混物中的羧基化聚丙烯组分可以发挥稀释剂的作用,大幅度降低了聚乳酸的冷结晶温度.聚乳酸含量≥50%时,共混熔体降温时DSC谱图中聚乳酸和羧基化聚丙烯分别结晶,而聚乳酸含量<50%时,只观察到羧基化聚丙烯的结晶行为.     

Effect of polyethylene glycol on the crystallization and impact properties of polylactide‐based blends

Polylactide (PLA) was plasticized by polyethylene glycols (PEGs) with five different molecular weights (M_w = 200–20,000 g/mol). The effects of content and molecular weight of PEG on the crystallization and impact properties of PLA were studied by wide‐angle X‐ray diffraction, differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, and V‐notched impact tests, respectively. The results revealed that PEG‐10,000 could significantly improve the crystallization capacity and impact toughness of PLA. When the PEG‐10,000 content ranged from 0 to 20 wt%, the increases in both V‐notched Izod and Charpy impact strengths of PLA/PEG‐10,000 blends were 206.10% and 137.25%, respectively. Meanwhile, the crystallinity of PLA/PEG‐10,000 blends increased from 3.95% to 43.42%. For 10 wt% PEG content, the crystallization and impact properties of PLA/PEG blends mainly depended upon PEG molecular weight. With increasing the M_w of PEG, the crystallinity and impact strength of PLA/PEG blends first decreased and then increased. The introduction of PEG reduced the intermolecular force and enhanced the mobility of PLA chains, thus improving the crystallization capacity and flexibility of PLA. Copyright © 2015 John Wiley & Sons, Ltd.     

New approach on the development of plasticized polylactide (PLA): Grafting of poly(ethylene glycol) (PEG) via reactive extrusion

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 T_g when 20 wt.% PEG were melt blended with neat PLA or 10 wt.% MAG-PLA. In the latter case, the T_g displayed by the reactive blend was shifted to even lower temperatures at around 14 °C, while the T_g 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.     

Homogeneous dispersion of chitin nanofibers in polylactic acid with different pretreatment methods

Chitin nanofibers extracted from crab shell were used to reinforce polylactic acid (PLA) by extrusion molding. The dispersion problem of nanofibers in PLA matrix was solved by three pretreatment methods, including water pretreatment, polyethylene glycol (PEG) pretreatment, and polyethylene oxide (PEO) pretreatment. The results demonstrated that chitin nanofibers were distributed uniformly on the fracture surface of the PLA matrix with three different pretreatment methods. However, the aspect ratio of nanofibers with was reduced with the PEG and PEO pretreatment methods. Therefore, the bending modulus (MOE), bending strength (MOR) and impact toughness of the chitin nanofibers/PLA composites prepared by the water pretreatment method were much higher than those of the composites prepared by the PEG and the PEO pretreatment method. Furthermore, the reinforcing effect with the PEG method is slightly better than that with the PEO method. Although it was found that both PEG and PEO were good interfacial compatibilizers for nanofibers and PLA, the reinforcing effect of the composites prepared by PEG and PEO pretreat methods was suppressed due to the decrease of the aspect ratio for chitin nanofibers.     

Interactions of adsorbed poly(ethylene oxide) mushrooms with a bare silica-ionic liquid interface

The interaction of adsorbed poly(ethylene oxide) (PEO) mushrooms with clean silica-ethylammonium nitrate (EAN, a protic ionic liquid) interfaces is investigated using atomic force microscopy (AFM). 10 kDa, 35 kDa and 100 kDa PEO was used to prepare polymer layers ex situ by drop casting from 0.01 wt% EAN solutions. AFM tapping mode measurements of dried, solvent free PEO layers revealed oblate structures, which increase in size with molecular weight. Colloid probe force curve measurements of these surfaces re-solvated with EAN suggest PEO adopts a mushroom morphology, with the interaction range (layer thickness) increasing with molecular weight. Attractive forces on approach and single strand stretching forces on retraction show PEO has a strong affinity for the silica-EAN interface. The single polymer strand stretching forces follow the freely jointed chain model under good solvent conditions. Contour lengths close to the theoretical limits of 120 nm for the 10 kDa, 290 nm for the 35 kDa and 1240 nm for the 100 kDa PEO samples are observed, while fitted Kuhn lengths are small, at 0.14 nm.     

Colloidal stability and drug incorporation aspects of micellar-like PLA–PEG nanoparticles

The drug delivery properties of a series of poly(lactic acid)–poly(ethylene glycol) (PLA–PEG) micellar-like nanoparticles have been assessed in terms of their colloidal stability and their ability to incorporate a water soluble drug. These studies have focused on a range of PLA–PEG copolymers with a fixed PEG block (5 kDa) and a varying PLA segment (3–110 kDa). In aqueous media, these copolymers formed micellar-like assemblies following precipitation from water miscible solvents. There was a controlled increase in the particle size as the molecular weight of the PLA block was increased. The characteristics of the PEG corona were also highly dependent on the PLA moiety. Copolymers with a low molecular weight PLA block (3–15 kDa) formed highly colloidally stable dispersions, with a complete PEG surface coverage. However, increasing the molecular weight of the PLA block resulted in significantly less colloidally stable nanoparticle dispersions, which flocculated in solvents that were significantly better than θ-solvents for the stabilising PEG chains. This can be attributed to a reduced PEG surface coverage and the probable presence of naked PLA ‘patches’ on the particle surface. These larger PLA–PEG nanoparticles (30:5–110:5) were found to be stabilised in the presence of serum components, which are thought to adsorb into the gaps on the particle surface and prevent flocculation. All of the dispersions were found to be stable under physiological conditions and therefore suitable for in vivo administration. A reasonable loading (3.1% w/w) of the micellar-like PLA–PEG 30:5 nanoparticles with the water soluble drug procaine hydrochloride was achieved. The incorporated drug was found to have no effect on the nanoparticle structure or recovery, which can be attributed to the micellar character of these assemblies and the presence of the stabilising PEG chains.     

Towards a microchip-based chromatographic platform. Part 1: Evaluation of sol-gel phases for capillary electrochromatography

Silica monolithic columns suitable for implementation on microchips have been evaluated by ion-exchange capillary electrochromatography. Two different silica monoliths were created from the alkyl silane, tetramethyl orthosilicate (TMOS), by introducing a water-soluble organic polymer, poly(ethylene oxide) (PEO), with varying molecular weights into the prehydrolyzed sol. Silica monoliths created using 10 kDa PEO were found to have a much more closed gel structure with a smaller percentage of pores in the microm size range than gels created using 100 kDa PEO. Additionally, the size of the mesopores in the 100 kDa PEO monolith was 5 nm, while those in the 10 kDa PEO gel were only 3 nm. This resulted in a strong dependence of the electroosmotic flow (EOF) on the ionic strength of the background electrolyte, with substantial pore flow through the nm size pores observed in the 10 kDa PEO gel. The chromatographic performance of the monolithic columns was evaluated by ion-exchange electrochromatography, with ion-exchange sites introduced via dynamic coating with the cationic polymer, poly(diallyldimethylammonium chloride) (PDDAC). Separating a mixture of inorganic anions, the 10 kDa PEO monolithic columns showed a higher effective capacity than the 100 kDa PEO column.     

The Synthesis of Poly(ethylene oxide)-Block-Polybutylacrylate

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Crystallization behavior of disproportionately high and low molecular weight PEO blends

The crystallization behavior of PEOs with molecular weight of 1 Ok and 200k as well as their blends was studied in details. The results show that the lower molecular weight PEO crystallizes with faster crystallization rate as judged from a shorter time for completing the crystallization. On the other hand, the higher molecular weight PEO crystallizes at relatively higher temperature, indicating an early start of crystallization compared with the lower molecular weight one. The blends of these two PEOs with different blend ratios always cocrystallize during the cooling processes. It is confirmed that mixing of the 10k PEO with the 200k one is in favor of the crystallization of the system. This is not only demonstrated by the early start of the crystallization at higher crystallization temperature, and also a faster crystal growth of the blend with respect to the 200k PEO. The crystallization of the blends at higher temperature is caused by an early start of nucleation and an increment of nucleus density. This may originate from the density fluctuation of the blend and a reduction in energy barrier for nucleation. Moreover, it is found that the crystallinity of the 1 Ok PEO rich blends increases with increasing concentration of the 10k PEO. This is caused by the solvent effect of the 10k PEO toward the 200k PEO. On the other hand, the crystallinity of the 30/70 （10k/200k） PEO blend is decreased a little bit. This may be a balanced result of the improved crystallization of the 200k PEO at the expense of the high crystallization ability of the 1 Ok PEO.     

High-Toughness Poly(lactic Acid)/Starch Blends Prepared through Reactive Blending Plasticization and Compatibilization

In this study, poly(lactic acid) (PLA)/starch blends were prepared through reactive melt blending by using PLA and starch as raw materials and vegetable oil polyols, polyethylene glycol (PEG), and citric acid (CA) as additives. The effects of CA and PEG on the toughness of PLA/starch blends were analyzed using a mechanical performance test, scanning electron microscope analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, X-ray diffraction, rheological analysis, and hydrophilicity test. Results showed that the elongation at break and impact strength of the PLA/premixed starch (PSt)/PEG/CA blend were 140.51% and 3.56 kJ·m⁻², which were 13.4 and 1.8 times higher than those of pure PLA, respectively. The essence of the improvement in the toughness of the PLA/PSt/PEG/CA blend was the esterification reaction among CA, PEG, and starch. During the melt-blending process, the CA with abundant carboxyl groups reacted in the amorphous region of the starch. The shape and crystal form of the starch did not change, but the surface activity of the starch improved and consequently increased the adhesion between starch and PLA. As a plasticizer for PLA and starch, PEG effectively enhanced the mobility of the molecular chains. After PEG was dispersed, it participated in the esterification reaction of CA and starch at the interface and formed a branched/crosslinked copolymer that was embedded in the interface of PLA and starch. This copolymer further improved the compatibility of the PLA/starch blends. PEGs with small molecules and CA were used as compatibilizers to reduce the effect on PLA biodegradability. The esterification reaction on the starch surface improved the compatibilization and toughness of the PLA/starch blend materials and broadens their application prospects in the fields of medicine and high-fill packaging.     

Blends of POSS-PEO(n=4)(8) and high molecular weight poly(ethylene oxide) as solid polymer electrolytes for lithium batteries

Solid polymer electrolyte blends were prepared with POSS-PEO(n=4)8 (3K), poly(ethylene oxide) (PEO(600K)), and LiClO4 at different salt concentrations (O/Li = 8/1, 12/1, and 16/1). POSS-PEO(n=4)8/LiClO4 is amorphous at all O/Li investigated, whereas PEO(600K) is amorphous only for O/Li = 8/1 and semicrystalline for O/Li = 12/1 and 16/1. The tendency of PEO(600K) to crystallize limited the amount of POSS-PEO(n=4)(8) that could be incorporated into the blends, so that the greatest incorporation of POSS-PEO(n=4)(8) occurred for O/Li = 8/1. Blends of POSS-PEO(n=4)(8)/PEO(600K)/LiClO4 (O/Li = 8/1 and 12/1) microphase separated into two amorphous phases, a low T(g) phase of composition 85% POSS-PEO(n=4)(8)/15% PEO(600K) and a high T(g) phase of composition 29% POSS-PEO(n=4)(8)/71% PEO(600K). For O/Li = 16/1, the blends contained crystalline (pure PEO(600K)), and two amorphous phases, one rich in POSS-PEO(n=4)(8) and one rich in PEO(600K). Microphase, rather than macrophase separation was believed to occur as a result of Li(+)/ether oxygen cross-link sites. The conductivity of the blends depended on their composition. As expected, crystallinity decreased the conductivity of the blends. For the amorphous blends, when the low T(g) (80/20) phase was the continuous phase, the conductivity was intermediate between that of pure PEO(600K) and POSS-PEO(n=4)(8). When the high T(g) (70/30, 50/50, 30/70, and 20/80) phase was the continuous phase, the conductivity of the blend and PEO(600K) were identical, and lower than that for the POSS-PEO(n=4)(8) over the whole temperature range (10-90 degrees C). This suggests that the motions of the POSS-PEO(n=4)(8) were slowed down by the dynamics of the long chain PEO(600K) and that the minor, low Tg phase was not interconnected and thus did not contribute to enhanced conductivity. At temperatures above T(m) of PEO(600K), addition of the POSS-PEO(n=4)(8) did not result in conductivity improvement. The highest RT conductivity, 8 x 10(-6) S/cm, was obtained for a 60% POSS-PEO(n=4)(8)/40% PEO(600K)/LiClO4 (O/Li = 12/1) blend.