稀释剂粘度对HDPE微孔膜微观结构影响

采用扫描电镜(SEM)研究了稀释剂(矿物油)粘度对热诱导相分离高密度聚乙烯(HDPE)微孔膜微孔结构的影响。结果表明,随着矿物油粘度的增加,在HDPE／矿物油体系冷却诱导相分离过程中,大量矿物油滞留在晶体内部,采用有机溶剂萃取后晶体问孔减小、减少。相比自然冷却,采用冰水混合物冷却得到的晶体间孔更小。最后从微孔膜加工性及微孔大小出发,认为具有中等粘度的稀释剂比较好。     

PTT/PE共混体系结晶动力学及结晶形态研究

采用差示扫描量热法(DSC)研究了聚对苯二甲酸丙二醇酯/聚乙烯(PTT/PE)共混体系的非等温结晶动力学,通过热台偏光显微镜(POM)对共混物在等温条件下的结晶形态进行了研究。结果发现:PTT/PE共混体系各样品的结晶峰温度随着冷却速率的提高而下降,而半结晶时间t1/2随着冷却速率的提高而提高;结晶动力学常数Zc随着冷却速率的提高而下降,表明共混体系的结晶速率随着冷却速率的提高而降低;在POM观察的时间范围内各样品的球晶尺寸随着时间的延长而增大,PTT/PE(30/70)共混体系在190℃结晶时,球晶尺寸较大,即球晶生长较快。     

PTT/PE共混体系结品动力学及结晶形态研究

采用差示扫描量热法(DSC)研究了聚对苯二甲酸乙二醇酯/聚乙烯(PTT/PE)共混体系的非等温结晶动力学,通过热台偏光显微镜(POM)对共混物在等温条件下的结晶形态进行了研究.结果发现:PTT/PE共混体系各样品的结晶峰温度随着冷却速率的提高而下降,而半结晶时间t1/2随着冷却速率的提高而提高;结晶动力学常数Zc随着冷却速率的提高而下降,表明共混体系的结晶速率随着冷却速率的提高而降低;在POM观察的时间范围内各样品的球晶尺寸随着时间的延长而增大,PTT/PE(30/70)共混体系在190℃结晶时,球晶尺寸较大,即球晶生长较快.     

PP/HDPE共混物的黏弹性对泡孔结构的影响

将聚丙烯(PP)分别与两种高密度聚乙烯(HDPE)共混,并采用超临界二氧化碳(SC-CO2)作为发泡剂进行高压釜发泡,得到PP/HDPE发泡材料。同时考察了PP/HDPE熔体的黏弹性,并研究了其对PP/HDPE发泡材料泡孔结构的影响。结果表明:PP与黏弹性低于其本身的HDPE共混时,随着HDPE含量的增加,熔体的黏弹性逐渐减小,其中当HDPE含量为25%时,能够得到均匀细小的微孔结构;PP与黏弹性高于其本身的HDPE共混时,随着HDPE含量的增加,熔体的黏弹性逐渐增大,但所得PP/HDPE发泡材料的泡孔尺寸、孔隙率却不减反增,且泡孔结构完整。     

PP/HDPE/滑石粉复合材料微孔发泡实验研究

为了改善聚丙烯(PP)的微孔发泡性能,将PP与高密度聚乙烯(HDPE)共混,提高其熔体强度;然后在PP/HDPE共混体系中加入少量滑石粉,研究滑石粉的用量对共混体系熔体强度及微孔发泡过程的影响。研究结果表明,滑石粉的加入使体系的熔体强度提高,发泡样品的泡孔结构变得更均匀。而且,随着滑石粉用量的增加,泡孔尺寸减小,泡孔密度增加。     

纳米CaCO_3对PP/HDPE共混体系微孔发泡过程的影响

聚丙烯(PP)是结晶性聚合物,熔体强度低,发泡性能差。为了提高PP的微孔发泡性能,本文首先将PP与高密度聚乙烯(HDPE)共混,提高其熔体强度;然后在PP/HDPE共混体系中加入少量纳米CaCO3,研究CaCO3的含量对共混体系熔体强度及发泡材料泡孔结构的影响。研究结果表明,纳米CaCO3的加入使体系的熔体强度提高,且随着CaCO3含量的增加,泡孔尺寸减小,泡孔密度增加。然而,加入CaCO3以后,泡孔结构不是很规整,泡孔分布不均匀。     

PET/PTT共混体系的非等温结晶动力学研究

采用DSC方法研究了PET/PTT共混体系的非等温结晶动力学,研究发现:PET/PTT共混体系各样品的结晶峰温度和半结晶时间t1/2随着冷却速率的提高而下降;结晶动力学常数Zc随着冷却速率的提高而增加,表明共混体系的结晶速率随着冷却速率的提高而增大;Zc随着PTT含量的增加而逐渐减小,在其含量达40%￣50%时出现了最小值。     

PHBV/PEA共混物结晶行为的研究

采用偏光显微镜(POM)和差示扫描量热仪(DSC)深入研究了不同配比的聚己酸戊酸共聚酯/聚己二酸乙二醇酯(PHBV/PEA)共混体系在不同结晶温度下的结晶形貌、结晶热力学以及结晶动力学。结果表明:随着结晶温度的升高,PHBV/PEA共混物中PHBV的球晶尺寸和环带间距均有所增大;随着PEA含量的增加,PHBV球晶尺寸增大,结构更加开放,同时共混物中PEA组分受PHBV组分的影响,由原来的大球晶变成了细小的碎晶。此外,同纯PHBV和纯PEA相比,PHBV/PEA共混体系中两种组分的结晶速率均有所降低。     

发泡杜仲胶/高密度聚乙烯形状记忆材料的制备与性能

通过物理共混的方式制备了发泡杜仲胶(EUG)/高密度聚乙烯(HDPE)形状记忆材料,探讨了共混比对其硫化特性、物理机械性能、发泡程度、结晶熔融行为和形状记忆性能的影响。结果表明,随着HDPE用量的增加,EUG/HDPE形状记忆材料的交联程度降低,100%定伸应力、300%定伸应力增大,但拉伸强度及扯断伸长率降低,物理机械性能与材料的交联结构、晶区、泡孔等微观结构密切相关;HDPE的加入使材料的发泡程度增大,EUG相的熔融温度及相对结晶度随着HDPE用量的增加而降低,HDPE的相对结晶度增大而熔融温度基本无变化;随着HDPE用量的增加,材料的热刺激响应温度Tr升高,形变回复速率Vr减小,热致形变回复率Rf无明显变化。     

轻量化杜仲胶/高密度聚乙烯形状记忆材料的制备与性能

以可膨胀物理微球Expancel 920 DU 40为发泡剂,通过物理共混和化学交联的方式制备了发泡杜仲胶(EUG)/高密度聚乙烯(HDPE)形状记忆材料,从而实现了轻量化。采用扫描电镜、差示扫描量热法和万能材料试验机等对不同共混比的发泡EUG/HDPE复合材料的微观形貌、结晶熔融行为、物理机械性能和形状记忆行为等进行了研究。结果表明,随着HDPE用量的增加,发泡EUG/HDPE形状记忆材料的交联程度和拉伸强度降低,定伸应力增大,物理机械性能与材料内部的交联结构、晶区、泡孔等微观结构密切相关;HDPE的加入使复合材料的发泡程度增大,EUG相的熔融温度和相对结晶度随HDPE用量的增加而降低,HDPE的相对结晶度增大而熔融温度基本无变化;随HDPE用量的增加,复合材料的热刺激响应温度升高,形变回复速率减小,热致形变回复率无明显变化。     

The influence of injection molding parameters and blowing agent addition on selected properties,surface state,and structure of HDPE parts

The investigation of the influence of injection molding parameters (injection velocity, mold temperature and injection temperature, and additionally, as a result of these three parameters change, injection time, hold time, and cooling time) and blowing agent percentage on selected properties of HDPE molded parts such as weight, density, mechanical properties (tensile strength and elongation at maximum force), surface state (gloss and color), and structure was the aim of this work. The examination showed, that the mold temperature has the main influence on properties and surface state of molded parts from solid and foam HDPE. The weight, density, mechanical properties and gloss of molded parts increased with the increase in mold temperature. The mold temperature also influences significantly the number and size of pores in molded parts. The addition of blowing agent in a quantity of 2% is sufficient to obtain parts with favorable mechanical properties and good surface quality. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.     

Shish and its relaxation dependence of re-crystallization of isotactic polypropylene from an oriented melt in the blends with high-density polyethylene

Shish structure and its relaxation dependence of re-crystallization of isotactic polypropylene (iPP) from an oriented melt, caused by melting of shish kebab in original samples (indicated by 2D SAXS and 2D-wide-angle X-ray scattering experiments (2D WAXS) measurements), has been investigated by differential scanning calorimetry (DSC) and optical microscopy (OM). Shish was obtained by dynamic packing injection molding and its size was controlled by addition of high-density polyethylene (HDPE). An increase in shish size was observed with increasing of HDPE content, as indicated by an increase in the crystallization temperature for iPP during re-crystallization. This is understood as, on one hand, the overall decrease in viscosity by addition of HDPE, thus an increase in shear rate. Higher shear rate can promote larger orientation of molecules and continuous growth of shish structure. On the other hand, the relaxation mode of shish in the melt while re-crystallization is also dominated by its size. Shish with larger size has higher thermal stability and can endure more duration time in the melt. Even more, shish with a larger size cannot be transformed to random coil entirely even subjected to annealing at 200 °C for 60 min, and thus re-crystallization via self-seeding is always observed on primary nuclei originated from shish structure. A permanent ordered structure, most likely with chain helical conformation, is proposed for iPP with large shish size. However, shish with smaller size can only maintain for a short time and then relax into random coil completely, resulting in almost absence of self-seeding in re-crystallization. Re-crystallization of isotactic polypropylene was discussed based on: (1) self-seeding with respect to size of shish structure and (2) relaxation of shish with different size.     

热致相分离法平片式聚(乙烯-乙烯醇)微孔膜的制备和表征

以丙三醇为稀释剂,用热致相分离方法(TIPS)制备了无纺布支撑的平片式聚(乙烯-乙烯醇)(EVOH)微孔膜。实验研究了冷却速率及EVOH初始浓度对膜结构及性能的影响,测定了EVOH／丙三醇体系的相图．用扫描电子显微镜(SEM)及泡点法表征了微孔膜的微观结构及表面孔径,同时测试了膜的纯水通量。结果表明,随着冷却速率的加快,结晶曲线向低温移动。EVOH初始浓度决定了体系的相分离方式．由液-液相分离及固-液相分离机理形成的膜分别具有花边结构与球间缝隙结构;冷却速率影响膜的孔径大小和形态。随着冷却速率及EVOH初始浓度的降低,膜的孔径及纯水通量均逐渐增大。     

Thermal characteristics and temperature profile changes of structurally different polyethylenes with peroxide modifications

Crosslinking and processing characteristics of polyethylenes (PEs) with different molecular architectures, namely high‐density polyethylene (HDPE), linear low‐density polyethylene (LLDPE), and low‐density polyethylene (LDPE), were studied with regard to the effects of peroxide modifications and coolant flow rates. Dicumyl peroxide (DCP) and di‐tert‐butyl peroxide (DTBP) were used as free‐radical inducers for crosslinking the PEs. The characteristics of interest included normalized gel content, real‐time temperature profiles and their cooling rates, exothermic period, crystallinity level, crystallization temperature, and heat distortion temperature. The experiments showed that LDPE exhibited the highest normalized gel content. The real‐time cooling rates, taken from the temperature profiles for all PEs before the crystallization region, were greater than those after the crystallization region. The cooling rate of the PEs increased with the presence of DCP, whereas the crystallization temperature of the PEs was lowered. The HDPE appeared to show the longest exothermic period as compared with those of the LLDPE and LDPE. The exothermic period showed an increase with increasing coolant flow rate, but it was decreased by the use of DCP. As for the effect of peroxide type, the gel content and cooling rate of the PE crosslinked by DCP were higher than those for the PE crosslinked by DTBP. The DTBP was the more effective peroxide for introducing crosslinks and simultaneously maintaining the crystallization behavior of the PE. J. VINYL ADDIT. TECHNOL., 20:80‐90, 2014. © 2014 Society of Plastics Engineers     

Morphology and mechanical properties of biaxially oriented films of polypropylene and HDPE blends

Biaxially oriented films of blends of high-density polyethylene (HDPE) with polypropylene (PP) homopolymer and PP copolymers prepared by twin-screw extrusion and lab-stretcher have been investigated by scanning electron microscopy (SEM), polarized microscopy, differential-scanning calorimeter, and universal testing machine. Three different kinds of PP copolymers were used: (i) ethylene–propylene (EP) random copolymer; (ii) ethylene–propylene (EP) block copolymer; (iii) ethylene–propylene–buttylene (EPB) terpolymer. In the SEM study of the morphology of films of HDPE with various PP blends, phase separation is observed between the PP phase and the HDPE phase for all blends and compositions. In all blends, HDPE serves to reduce the average spherulites size, probably acting as a nucleating agent for PP. The reduction of spherulite size appeared most significantly in the blend of EPB terpolymer and HDPE. A large increase of crystallization temperature was found in the blend of EPB terpolymer and HDPE compared with the unblended EPB terpolymer. For the blend of EPB terpolymer and HDPE, the improvement of tensile strength and modulus is observed with an increase of HDPE content, and this can be considered as a result of the role of HDPE in reducing average spherulite size. © 1994 John Wiley & Sons, Inc.     

Influence of cocrystallization behavior on structure and properties of HDPE/LLDPE microporous membrane

The microporous membranes of high-density polyethylene (HDPE) and linear- lower-density polyethylene (LLDPE) blend were prepared based on melt-stretching mechanism and the influence of cocrystallization behavior on the structure and properties of stretched microporous membranes was investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS) and capillary flow porometer. It was found that compared with that without LLDPE, the main melting peak and the maximum crystallization temperature of HDPE/LLDPE blend precursor film with LLDPE content up to 12 wt.% were moved to lower temperature. The crystallinity of HDPE/LLDPE blend with LLDPE content of 5 wt.% was increased from 65.8 to 73.0 % due to the existence of cocrystallization behavior. The porosity and air permeability property of corresponding stretched microporous membrane were decreased by 7.1 and 44.4 %, respectively, whereas the puncture resistance was increased by 111.4 %. But further increase of LLDPE content to 12 wt.% lead to the decrease of cocrystallization ability and puncture resistance. To obtain final microporous membrane with better puncture resistance, adding 5 wt.% LLDPE to HDPE is appropriate. At the same time, although the air permeability is decreased, the value is still acceptable for the application of this kind of microporous membrane in the field of Li-ion battery as a separator.     

Effects of processing parameters on axial stiffness of self‐reinforced polyethylene composites

Self‐reinforced polyethylene composites have proven to be promising candidate materials for a number of wear‐resistance and bioimplant applications. In this study, we investigated the effects of processing parameters on the elastic modulus of self‐reinforced high‐density polyethylene (HDPE) composites. The processing parameters investigated were the cooling rate, processing pressure, temperature, and duration. Our results showed an optimum processing temperature, pressure, and duration that were matrix‐dependent. In addition, for an HDPE matrix, the slower the composite cooling rate was, the higher the composite modulus was. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1136–1141, 2001     

Influence of temperature schedules on particle size and crystallinity of titania synthesized by vapor-phase oxidation route

Crystalline TiO₂ particles were produced in a tubular flow reactor by chemical vapor synthesis using titanium tetrachloride as a starting material in oxygen containing atmospheres. The dependence of particle size, morphology and crystalline phase of titania on temperature schedules including the reactor temperature, the oxygen preheated temperature and the product cooling measure were explored. It is found that there are two opposite effects of temperature on particle size and crystalline phase content. The particle size distribution, SEM and TEM of resulting powders show that the grain size is controlled by the relative magnitudes of the nucleation rate and growth rate, both of them being subject to the temperature schedules. XRD indicates that particles crystalline phase is predominately anatase and the rutile content increment is not consistent with temperature increase. Anatase titania can be converted to rutile by addition of crystal modifier AlCl₃. The element analysis by EDS shows that Al enriches on the particle outer surface.     

Linear low-density polyethylene/high-density polyethylene blends: Effect of high-density polyethylene content on die swell and flow instability

This work aimed to evaluate the effect of high-density polyethylene (HDPE) content and of shear rate on the die swell and flow instability of linear low-density polyethylene (LLDPE)/HDPE blends. The results showed that the die swell of the LLDPE/HDPE blends increased with the increase in the shear rate. At high shear rates, the increase in the HDPE content led to an increase in the die swell of LLDPE/HDPE blends. The surface morphology analysis of the extrudates by optical and scanning electron microscopy revealed the presence of sharkskin and stick–slip flow instabilities in LLDPE and LLDPE/HDPE blends at the shear rates investigated. These instabilities were attenuated with the addition of HDPE and almost disappeared in the LLDPE/HDPE blend containing 50 wt% of HDPE.