The influence of molecular weight on the large deformation behavior of SBS triblock copolymer elastomers

Engineering stress–strain properties were determined for two polystyrene–polybutadiene–polystyrene (SBS) triblock copolymer elastomers, one consisting of blocks of molecular weight 7000/43000/7000 and the other, 16000/85000/17000. In addition, various blends of these two materials were prepared in order to vary the number-average molecular weight of the blocks in a systematic way while maintaining polystyrene content in the range of 25–28 wt %. Samples were solvent cast from benzene or benzene/heptane mixtures and annealed before testing. Ring specimens were extended to rupture at varying strain rates on an Instron tensile tester. Results indicate that number-average molecular weight has a marked influence on stress–strain behavior over the range of molecular weights and testing conditions employed. The observed behavior is consistent with a systematic increase in the proportion of a mixed interfacial region between the pure polystyrene and polybutadiene domain as molecular weight decreases. The interfacial region contributes to mechanical hystersis, rate sensitivity, and toughness in the SBS materials. Scanning electron photomicrographs of fracture surfaces also showed systematic changes with molecular weight.     

Preparation of biodegradable polymer microspheres encapsulating protein with micron sizes

Biodegradable polymer poly-D,L -lactide-polyethylene glycol (PLA-PEG) was synthesized with stannous octoate (SnOc₂) as catalyst by a cationic ring-opening polymerization. The molecular weight of PLA-PEG is the highest at a content of 0.1% SnOc₂. The PLA-PEG microspheres carrying protein were prepared by a solvent evaporation composite emulsion technique with a narrow size range (1–2 μm). The sizes of PLA-PEG microspheres increased with the increase of the molecular weight of PLA-PEG. The PEG in PLA-PEG (10%) significantly improved the size control of the microspheres of the PLA family as a drug carrier matrix. Polyvinyl alcohol (PVA) aqueous solution was used as dispersion medium for microsphere preparation. The concentration of the PVA solution can affect the size of the PLA-PEG microspheres. The differential scanning calorimetry data showed that the PLA-PEG microspheres can efficiently encapsulate the protein and that the crystalline of the microspheres carrying protein was lower than that of the nonprotein-loading microspheres. The amount of protein carried in the PLA-PEG microspheres was related to the nature of the protein itself. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 583–590, 1997     

On-line studies of structure development during melt spinning of poly(butylene terephthalate)

An on-line study of structure development during poly(butylene terephthalate) melt spinning was carried out. Two polymers with different molecular weights (intrinsic viscosities of 0.75 and 1.0 dL/g) were used. The range of take-up velocities studied was 1500 to 4500 m/min. On-line measurements included diameter, temperature, birefringence, and tension. The phenomenon of diameter thinning (necking) was observed for both polymers at take-up velocities of 3500 and 4500 m/min with a mass throughput of 4 g/min. At a constant mass throughput, the distance from the spinneret at which the necking occurred varied with take-up velocity and molecular weight of the polymer. Increasing the take-up velocity at constant mass throughput caused an increase in cooling rate and a slight increase in the rate at which the temperature decreased with distance from teh spinneret. A small but detectable change in the rate of temperature decrease was observed at a position near or just beyond the formation of the neck. It is suggested that this effect is due to the increased heat transfer caused by the rapid increase in filament velocity and increased surface to volume ration in the neck. Increased take-up velocity also caused necking to occur at higher temperature, as did an increase of polymer molecular weight. Birefringence increased with distance from the spinneret and indicated substantial molecular orientation was developed in the filament prior to the necking zone. A sharp increase of birefringence in the necking zone was observed for take-up velocities of 3500 and 4500 m/min. A discussion of the mechanism of neck formation is presented, and it was concluded that necking is intimately associated with stress-induced crystallization in PBT. An increase of spinline stress resulting from either an increase of take-up velocity or an increase of molecular weight can cause stress-induced crystallization and, hence, necking to occur nearer the spinneret and at higher temperature. For a given polymer this leads to filaments with higher levels of crystallinity, crystalline orientation, and crystalline perfection (greater crystal size). These changes in morphology result in changes in the filament mechanical properties. The effect of molecular weight change on the structure and properties is complicated by the fact that the development of crystallinity seems to be affected by the molecular weight independent of the spinline stress.     

聚乙二醇改性聚乳酸幽门螺杆菌微球疫苗的制备与体外控释

目的 应用聚乳酸与聚乙二醇共聚物（ＰＥＬＡ）包裹Ｈｐ超声上清液,制备 Ｈｐ口服微球疫苗,探讨共 聚物ＰＥＬＡ总相对分子质量ｒ、ＰＥＧ含量与不同相对分子质量ＰＥＬＡ共聚物的相对分子质量分布（Ｍｒ／Ｍｎ）对微球疫 苗体外释药特性的影响。方法　采用复乳法溶剂挥发技术,制备Ｈｐ微球疫苗,用电子显微镜与扫描电镜观测微球 疫苗的粒径,用紫外光谱分光光度法测定抗原包裹效率与Ｈｐ抗原释放量,并在ｐＨ７．３、浓度为 ０．０１ｍｏｌ／Ｌ的ＰＢＳ溶 液中作体外控释实验。结果 Ｈｐ微球疫苗抗原包裹效率在７５％左右,平均粒径在５１μｍ以下。若ＰＥＧ量低于 １０％,ＰＥＬＡ组成对微球疫苗的粒径和抗原包裹效率影响不大。结论 Ｈｐ抗原体外释放量与 ＰＥＬＡ中ＰＥＧ的量和 相对分子质量、ＰＥＬＡ的相对分子质量分布成正比,而与ＰＥＬＡ的总相对分子质量成反比。     

PELA-OmpK微球疫苗的部分特征及其对鲫鱼的口服免疫效果

目的研究聚-DL-乳酸-聚乙二醇共聚物(DL-polylactide-co-polyethylene glycol,PELA)包裹哈维弧菌(Vibrio har-veyi,Vh)重组外膜蛋白OmpK制备的微球疫苗的部分特性及其对鲫鱼(Carassius auratus gibelio)的口服免疫效果。方法用可生物降解的合成高分子材料PELA,通过乳化溶剂挥发法包裹OmpK,制备微球疫苗,Bradford法测定蛋白浓度,计算蛋白包裹率;通过扫描电镜观察微球粒径大小及其在4℃保存不同时间的形貌。取鲫鱼随机分为3组:微球疫苗组、OmpK蛋白组和空白对照组,前两组采用疫苗或蛋白拌饲投喂方式口服免疫,投喂3 d,间隔7 d,再投喂3 d加强免疫;对照组投喂不含疫苗的饲料。加强免疫4周和8周后,经腹腔注射20 LD50的Vh EcGS020802株攻击,记录各组鱼死亡数,计算相对免疫保护率。结果制备的PELA-OmpK微球疫苗中OmpK蛋白的包裹率达78%。微球粒径小于12μm,且90%微球的粒径小于5μm。4℃保存10 d微球表面光滑、圆整;保存30 d PELA微球降解,粒径较大的微球表面出现空洞;保存60 d可见大量碎片,微球表面毛糙松散,出现多个空洞。微球疫苗加强免疫鲫鱼4周和8周后,对活菌攻击的相对免疫保护率分别为70%和48%,而口服OmpK蛋白组和空白对照组鱼全部死亡。结论用PELA包裹裸疫苗制备成微球疫苗,对抗原具有一定的保护作用,PELA用作鱼类口服疫苗的投递载体是可行的。     

毛细管破碎法制备海藻酸微囊

建立了毛细管破碎装置制备海藻酸微囊。考察了海藻酸粘度、液流速度、针头直径和破碎频率对微囊的粒径及粒径分布的影响。试验结果表明 ,粘度为 4 5— 5 80mPa·s制备的海藻酸微囊球形度较好。在适宜的破碎频率和流速下 ,微囊粒径约为 1mm ,粒径偏差 <10 %。在低粘度体、较高流速与较大优化频率下 ,操作条件近似符合Weber线性理论。     

空心壳聚糖微球对二甲酚橙的吸附性能研究

采用反相悬浮交联法制备了具有空壳结构的壳聚糖微球。利用静电引力对二甲酚橙的进行吸附研究。通过分光光度法探讨了溶液初始DH值、吸附时间、二甲酚橙的初始质量浓度、吸附剂的用量及其粒径大小对二甲酚橙的吸附率的影响。结果表明：在DH值为4．90及常温下,二甲酚橙溶液的初始质量浓度为32mg／L时,可达到吸附平衡,此时的吸附剂用量为0．03g／100mL,吸附平衡时间约为2h,吸附率可高达93．6％。结果表明,此微球具有很强的吸附能力,而且平衡时间快,并且具有一定的重复利用的性能,是一类很值得开发的新型吸附分离材料。     

膜技术在油田采出水处理中的应用研究

采用无机陶瓷膜处理设备处理宝浪油田采出水,研究结果表明:处理后的采出水完全能满足宝浪油田注水的水质要求。产出水中的悬浮物含量小于1mg/L。0.1μm膜处理后的采出水中悬浮物含量平均值为0.417mg/L,粒径中值小于1μm;0.2μm膜处理后的采出水中悬浮物含量平均值为0.57mg/L,粒径中值小于1.5μm;产出水中油含量低于检测限;膜清洗周期为85个小时;清洗方法简单;膜通量的恢复率为99.93%。     

奥曲肽长效生物可降解微球的制备工艺研究

运用复乳法制备奥曲肽PLGA长效生物可降解微球,并用正交法优化微球制备工艺。利用HPLC、显微镜、激光粒度仪等对微球进行综合质量研究。结果表明,复乳法制备奥曲肽微球的最佳工艺参数为:内水相药物与中油相PLGA的质量比为1∶5,中油相PLGA的浓度为10%,外水相乳化剂为1%的22 000分子量聚乙烯(PVA)水溶液,中油相与外水相的体积比不小于1∶50,复乳化采用机械搅拌法,搅拌速度为1 200 r/min。在该工艺条件下制得的微球,包封率为35.1%,载药量为2.98%,平均粒径为26.3μm,微球外观圆整,形态良好。     

遇水崩解型聚苯乙烯崩解性能的研究

采用原位共混聚合法制得遇水崩解型聚苯乙烯(WDPS),对WDPS遇水崩解性能的影响因素进行了研究,包括聚丙烯酸钠(PAANa)高吸水树脂的粒径、吸水倍率,聚苯乙烯(PS)的分子量、表面活性剂Span-80等。结果表明:PAANa的粒径越小,越有利于WDPS的崩解;PAANa的吸水倍率在980g/g以上时,WDPS可以在72h内彻底崩解;PS重均分子量为1.3×105,既能使WDPS具有较好的崩解性能,又能使其保持一定的机械强度;表面活性剂Span-80含量占单体苯乙烯质量的3%时,WDPS崩解性能良好。     

Poly(dimethylsiloxane)‐toughened syntactic foams

The potential of preformed elastomers as a toughening agent for epoxy–glass syntactic foam has been explored. Poly(dimethylsiloxane) microspheres were prepared by suspension polymerization. The microsphere dimensions could be varied from 58 to 255 µm by tuning the reaction parameters, particularly the stirring speed and feed concentration. Rheological studies indicated that the introduction of microballoons led to an increase in the viscosity of the resin, with the extent being proportional to the microballoon content. The zero shear viscosity increased from ～10³ mPa s at 30 °C to 10⁵ mPa s as the microballoon loading was increased to 40%. Syntactic foams containing varying amounts of microballoons (40–60% v/v) were prepared, and an analogous set of toughened foams were also prepared, where a fraction of the microballoons was replaced with poly(dimethylsiloxane) microspheres (3–7%). The effect of increasing dimensions of the elastomeric microspheres on the mechanical properties was also studied. The improvement in properties was more pronounced when the microsphere size was equivalent to that of the constituent microballoons. An improvement of 40% and 185% in flexural strength and flexural toughness was observed upon the introduction of poly(dimethylsiloxane) microspheres of optimal dimensions (diameter ～63 µm, 5% loading), without any undesirable increase in foam density. However, the compressive properties remained practically unaltered. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45882.     

Effects of sorbed water on properties of low and high molecular weight PMMA: 1. Deformation and fracture behaviour

The influence of sorbed water on deformation and fracture behaviour of both low and high molecular weight poly(methylmethacrylate) has been investigated. In the low molecular weight polymer, addition of water produces a rise in internal friction in the ?100°C region but it has no apparent effect on the β-relaxation process. The tensile strength falls gradually with increasing concentration of water and more rapidly at high concentrations. Ductility initially increases with increasing water content but it reduces at high concentration. In the high molecular weight polymer, in contrast to the low molecular weight material, a yield maximum is observed for both dry and air-equilibrated samples of low moisture content and some samples show both necking and cold drawing prior to fracture. Observed deformation modes include shear bands, crazes, and diamond-shape surface cavities. However, water saturated samples fail in a brittle manner. From the observed deformation behaviour, as well as from observation of fracture surface morphology, it is suggested that sorbed water acts as a mild plasticizer for PMMA up to a concentration of about 1.1 % and, at higher water concentration, water clustering occurs.     

Preparation of ultrafine polyurethane fiber web by laser‐electrospinning combined with air blowing

Thermoplastic polyurethane fiber webs were prepared using a laser‐heated electrospinning process combined with air blowing. The effect of spinning conditions such as air flow rate and air temperature on fiber diameter and molecular weight was investigated. Although the average fiber diameter decreased with increased air flow rate at each air temperature, the diameter increased when the air flow rate was >15 NL min^?1. In addition, the fiber was comparatively thicker with an increase in the air temperature. The variation in the fiber diameter tends to increase with the air flow rate, and a reduction in the molecular weight of the fiber by thermal degradation was suppressed. The thinnest and most uniform fiber with a diameter of 0.9 µm and a diameter coefficient variation of 15% was obtained at an air temperature of 25°C under an air flow rate of 15 NL min^?1. This fiber also had a minimum of decreased molecular weight. POLYM. ENG. SCI., 54:2605–2609, 2014. © 2013 Society of Plastics Engineers     

磁性纤维直径对捕集Fe基细颗粒影响数值模拟

为了实现对钢铁行业微细颗粒的超低排放,提出磁性纤维提高对Fe基细颗粒物的捕集.基于计算流体力学-离散相模型CFD-DPM对比研究了传统纤维、磁性纤维直径对Fe基细颗粒捕集效率以及过滤阻力的影响.结果表明:当风速为0.10 m/s时,对于直径为35～45μm范围的纤维,直径的增大能够明显增加过滤阻力.对于粒径小于2.5 ...     

Effect of polyethylene glycol on the performance of ultrahigh‐molecular‐weight polyethylene membranes

Porous, flat membranes of ultrahigh‐molecular‐weight polyethylene (UHMWPE) were prepared by thermally induced phase separation, with mineral oil as a diluent and poly(ethylene glycol) with a weight‐average molecular weight of 20,000 (PEG20000) as an additive. Through the control of the rheological behavior, crystallite size, and pore structure, the influential factors, including the diluent, poly(ethylene glycol) (PEG) content, and cooling rate, were investigated. The results suggested that PEG could decrease the viscosity of UHMWPE/diluent apparently. The crystal density decreased when mineral oil was added, which made the melting point and crystallinity of UHMWPE lower. The crystallization rate and crystallinity also increased with the addition of PEG. However, the addition of excess PEG restrained crystal growth. PEG20000 in membranes could be extracted absolutely through the soaking of the membranes with fresh water for 7 days. With increasing PEG content, both porosity and pure water flux first increased and then decreased, reaching a maximum at a PEG mass fraction of 10%. The cooling rate had a direct effect the crystal structure. A slow cooling rate was good for crystal growth and diluent integration. Therefore, the pure water flux increased along with the temperature of the cooling medium, whereas porosity first increased and then decreased, reaching a maximum at 40°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

碱渗透溶胀法制备中空结构聚合物微球

采用预乳化饥饿型滴加方法结合碱溶胀处理制备了聚(甲基丙烯酸-甲基丙烯酸甲酯-丙烯酸正丁酯)/聚(甲基丙烯酸甲酯-苯乙烯-甲基丙烯酸)中空聚合物微球。试验集中讨论了种子阶段粒子大小,种子阶段引发剂用量、扩径时不同核壳比及不同碱进行碱处理时对形成中空聚合物微球的影响。同时采用TEM观察聚合物微球结构。试验所得的聚合物微球外径约为400 nm,内径约为220 nm。     

Solvent effect on TEMPO-mediated living free radical dispersion polymerization of styrene

Living free radical dispersion polymerization of styrene in the presence of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and 2,2-azobisisobutyronitrile (AIBN) was conducted in various glycol media having different solubility parameters. Genuine heterogeneous polymerization nature was observed from the initial stage of the reaction. The solubility parameter of the media was found to significantly influence the living characteristics of the polymerization including the polymerization kinetics and the molecular weight evolution at a fixed concentration of TEMPO. A grafting of stabilizer molecules onto monomer and a possible partitioning of TEMPO between the continuous medium and particle phase were postulated for the deviation of the experimentally obtained molecular weight from the calculated value. For a poor medium for styrene, such as diethylene glycol, the living nature was achieved by increasing the amount of TEMPO. The polystyrene (PS) microsphere was well obtained in all tested glycol media and the average size was increased with enhanced affinity of the media to styrene and with decreasing concentration of TEMPO.     

Effect of the preparation conditions on the permeation of ultrahigh‐molecular‐weight polyethylene/silicon dioxide hybrid membranes

Porous ultrahigh‐molecular‐weight polyethylene/SiO₂ membranes were prepared by thermally induced phase separation (TIPS) with white mineral oil as the diluent and SiO₂ as an additive. Influential factors, including extraction method, SiO₂ content, and cooling rate, were investigated. The results suggest that the both porosity and pure water flux of the membranes by extraction of the solvent naphtha in the tension state with alcohol were the best among our research. With increasing SiO₂ content, the porosity, pure water flux, and pore diameter increased. However, with excessive SiO₂ content, defects formed easily. Moreover, SiO₂ improved the pressure resistance of the membranes. The cooling rate directly effected the crystal structure. A slow cooling rate was good for crystal growth and the integration of the diluent. Therefore, the porosity, pure water flux, and bubble‐point pore diameter increased with decreasing cooling rate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High‐density polyethylene foams. I. Polymer and foam characterization

The density and morphology of closed‐cell high‐density foams were investigated with four different molecular weights of high‐density polyethylene (HDPE). The characterization of polyethylene via rheological methods was used to determine its influence on foam density and morphology. We found that foaming grade decreased with increasing molecular weight and increased with blowing agent content. The average cell size was also a strong function of molecular weight and blowing agent content. Increasing both the molecular weight and amount of blowing agent decreased the cell size. Cell size also increased for our lowest molecular weight HDPE but decreased for the others. Cell density also increased with increasing HDPE molecular weight. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2111–2119, 2003     

Properties of glass‐filled thermoplastic polyesters

The thermal, mechanical, and rheological properties of glass‐filled poly(propylene terephthalate) (GF PPT) were compared to glass‐filled poly(butylene terephthalate) (GF PBT). The impetus for this study was the recent commercial interest in PPT as a new glass‐reinforced thermoplastic for injection‐molding applications. This article represents the first systematic comparison of the properties of GF PPT and GF PBT in which differences in properties can be attributed solely to differences in the polyester matrices, that is, glass‐fiber size and composition, polymer melt viscosity, nucleant content and composition, polymerization catalyst composition and content, and processing conditions were kept constant. Under these controlled conditions, GF PPT showed marginally higher tensile and flexural properties and significantly lower impact strength compared to GF PBT. The crystallization behavior observed by cooling from the melt at a constant rate showed that GF PBT crystallized significantly faster than did GF PPT. Nucleation of GF PPT with either talc or sodium stearate increased the rate of crystallization, but not to the level of GF PBT. The slower crystallization rate of GF PPT was found to strongly affect thermomechanical properties of injection‐molded specimens. For example, increasing the polymer molecular weight and decreasing the mold temperature significantly increased the modulus drop associated with the glass transition. In contrast, the modulus–temperature response of GF PBT was just marginally influenced by the polymer molecular weight and was essentially independent of the mold temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 889–899, 1999