等通道转角挤出制备自增强等规聚丙烯的结构与性能研究

采用等通道转角挤出方法对等规聚丙烯进行自增强挤出,研究和分析挤出工艺条件与材料结构、性能之间的关系。利用广角X-射线衍射、差示扫描量热分析等手段对材料结构进行表征。结果表明:经过等通道转角挤出后等规聚丙烯的结晶度提高、晶粒细化、熔点提高,形成明显的取向结构,经过3次等通道转角挤出,等规聚丙烯的拉伸强度由挤出前的17.13MPa提高到59.38MPa。     

Flaking and extrusion as mechanical treatments for enzyme-assisted aqueous extraction of oil from soybeans

Flaking and extruding dehulled soybeans were evaluated as a means of enhancing oil extraction efficiency during enzyme-assisted aqueous processing of soybeans. Cellulase, protease, and their combination were evaluated for effectiveness in achieving high oil extraction recovery from extruded flakes. Aqueous extraction of extruded full-fat soy flakes gave 68% recovery of the total available oil without using enzymes. A 0.5% wt/wt protease treatment after flaking and extruding dehulled soybeans increased oil extraction recovery to 88% of the total available oil. Flaking and extruding enhanced protease hydrolysis of proteins freeing more oil. Treating extruded flakes with cellulase, however, did not enhance oil extraction either alone or in combination with protease. Discrepancies in oil extraction recoveries were encountered when merely considering crude free fat because some oil became bound to denatured protein during extrusion and/or sample drying. Bound fat was unavailable for determination by using the hexane extraction method, but was accounted for by using the acid hydrolysis method for total oil determination. Oil extraction recovery from extruded soybean flakes was affected by oil determination methods, which was not the case for unextruded full-fat soy flour.     

Effect of ultrasound on the morphology and properties of polypropylene/inorganic filler composites

The effects of ultrasonic irradiation on the rheology, structure, and properties of PP/inorganic filler composites were studied. Scanning electron microscopy showed that ultrasound increased the orientation degrees of acicular fillers to the flow direction. WAXD indicated that ultrasound vibration induced sheet fillers orient with its surface perpendicular to the direction of the ultrasound vibration. The orderly rearrangements of fillers in the polymer melt induced by ultrasound vibration can reduce the steric hindrances in the flow field and increase the flowability of the PP/inorganic filler composites. The effect of ultrasound on reducing the apparent viscosities is very prominent, especially at lower shear rate. Ultrasound has an even more marked effect on reducing the apparent viscosities of composites containing fillers of larger size. With ultrasound vibration, the mechanical properties of the composites are also improved because of the orientation and uniform dispersion of fillers in the matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1553–1560, 2005     

聚乙烯电缆料的高速挤出技术

研究了聚乙烯绝缘料的高速挤出特性。结果表明：通过共混改性，添加合理的助剂及良好的工艺条件能较好地实现PE电缆绝缘料的高速挤出。     

Paste extrusion of polytetrafluoroethylene (PTFE): Surface tension and viscosity effects

The effects of the lubricant physical properties on the processing of polytetrafluoroethylene (PTFE) fine powder resins are studied. Lubricants having different surface tension and viscosity were used; the two properties changed independently. These effects were studied by using dies of various contraction angle and reduction ratio for resins having a variety of molecular architecture. It was found that the wettability (surface tension) of the lubricant strongly affects the pressure needed to extrude the PTFE pastes. The viscosity of the lubricant was also found to play a significant role in the process since a lubricant with a low viscosity causes the paste to be extruded at a lower pressure. These effects of the physical properties on the extrusion pressure influence significantly the mechanical properties of the final extrudates. The latter are functions of the degree of fibrillation, which is significantly influenced by the wettability and viscosity of lubricants. Finally, the effects of die geometry on extrusion pressure and mechanical properties of extrudates were also assessed in order to determine the geometrical characteristics and operation conditions for the optimization of the process.     

In situ formation and compounding of polyamide 12 by reactive extrusion

The anionic polymerization of lauryllactam was initiated at 270°C using sodium hydride as an initiator and N,N′‐ethylene‐bisstearamide (EBS) as an activator (NaH:EBS molar ratio of 2). Polymerization occurred in less than 2 min and was successfully performed in an internal mixer and a twin‐screw extruder with corotating intermeshing screws (Werner & Pfleiderer ZSK 25). The content of residual monomer, as determined by thermogravimetric analysis, was lower than 0.5 wt %. Molecular weight, as measured by size exclusion chromatography, was governed by the lauryllactam:NaH molar ratio calculated on a M_n of 25 kg/mol at a constant NaH:EBS molar ratio of 2. Blends were prepared in situ by polymerization of lauryllactam solutions of various polymers. When poly(ethylene‐co‐butylacrylate) (Lotryl®; Atofina) was dissolved in lauryllactam, rubber‐toughened polyamide 12 blends were obtained. Mechanical properties of the injection‐molded polymers were examined by stress–strain as well as notched Charpy impact tests at different temperatures. Blend morphologies were imaged by scanning electron microscopy (SEM). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 344–351, 2003     

聚烯烃接枝马来酸酐的反应挤出研究

研究了聚乙烯（PE），聚丙烯（PP）接枝马来酸酐（MAH）的反应挤出，进行了反应体系的热分析，讨论了引发剂过氧化二异丙苯（DCP）和PE／DCP和PP／DCP体系的影响，以及DCP、MAH和电子给予体（EDA）和LDPE／DCP／MAH和PP／DCP／MAH两种接枝体系的影响。     

Thermoplastic extrusion—the mechanism of the formation of extrudate structure and properties

Systems processed by thermoplastic extrusion can be regarded as heterophase polymer melts of incompatible water-plasticized biopolymers. In the process of thermoplastic extrusion, proteins and polysaccharides are melted at high pressure and temperature below the temperature region of their thermal decomposition. Dispersed particles of these systems can be deformed in flow. The mixed-melt anisotropic structure, formed in flow, is fixed by rapid conversion of the melt jet that lets the extruder die from a viscous state to a rubber-like state and then to a glassy state caused by cooling and drying. Incompatibility of proteins and polysaccharides in their water-plasticized melt mixtures impacts on structure formation and texturization during thermoplastic extrusion. Presented at the 20th ISF World Congress and 83rd AOCS Annual Meeting and Expo, May 10–14, 1992, Toronto, Ontario, Canada.     

衣架式机头口模设计公式的修正探讨

基于表征值方法和熔体等压线平行于模唇这一流动模型,对衣架式机头口模进行了流动分析,并发现了文献[1]提出的口模设计公式中的一个缺陷,即计算的扇形狭缝区域与歧管发生了分离,针对该缺陷给出了修正公式。     

辐照改性聚丙烯拉伸流变行为及其挤出发泡的研究

通过在线形聚丙烯中加入双官能团丙烯酸酯类单体,经小剂量γ射线高能辐照,制备了高熔体强度聚丙烯,研究了其拉伸流变行为及其在挤出发泡方面的应用。Rheotens拉伸流变测试表明,辐照改性后由于形成了长支化分子结构,聚丙烯的熔体强度、拉伸黏度显著提高,具有明显的应变硬化特征。实验表明,ZnO可明显降低AC发泡剂分解温度,缓和分解放热;在辐照改性制备的高熔体强度聚丙烯中加入AC／ZnO复合发泡剂,可挤出发泡得到泡孔尺寸较为均一、分布均匀、具有闭孔结构的发泡材料。