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排序方式: 共有1475条查询结果,搜索用时 15 毫秒
1.
The aim of this work was to establish the important parameters that control the hot compaction behaviour of woven oriented polypropylene. Five commercial woven cloths, based on four different polypropylene polymers, were selected so that the perceived important variables could be studied. These include the mechanical properties of the original oriented tapes or fibres, the geometry of the oriented reinforcement (fibres or tapes), the mechanical properties of the base polymer (which are crucially dependant on the molecular weight and morphology), and the weave style. The five cloths were chosen so as to explore the boundaries of these various parameters, i.e. low and high molecular weight: circular or rectangular reinforcement (fibres or tapes): low or high tape initial orientation: coarse or fine weave.A vital aspect of this study was the realisation that hot compacted polypropylene could be envisaged as a composite, comprising an oriented ‘reinforcement’ bound together by a matrix phase, formed by melting and recrystallisation of the original oriented material. We have established the crucial importance of the properties of the melted and recrystallised matrix phase, especially the level of ductility, in controlling the properties of the hot compacted composite. 相似文献
2.
The formation of a crosshatched morphology during crystallization of an isotactic polypropylene with low crystallinity is studied in detail. Here, a lamella seems to grow through another nearly perpendicular lamella that was crystallized before. The crystallization was observed with in situ scanning force microscopy with a temporal resolution of 3 min per image. After crystallization the volume structure was imaged by nanotomography. A detailed scheme for the nucleation of branches is proposed. 相似文献
3.
Wettability of polyimide (PI) and polypropylene (PP) films have been improved using SiOx-like thin layers deposited from a mixture of hexamethyldisiloxane (HMDSO) and oxygen in a microwave distributed electron cyclotron resonance plasma reactor. The films wettability evolution behaviors were evaluated through the results of contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The plasma depositions of SiOx thin layers in presence of VUV radiation induce a contact angle decrease to about 7° and 35° for PI and PP films, respectively. XPS data showed that such difference in wettability is attributed to the increase of hydrophilic group's proportion at the surface of coated PI films due to VUV irradiation. AFM images showed that the PI surface topography remains relatively smooth when coated in presence of VUV radiation. However, in the case of PP films, AFM images revealed the growth of irregular structure due to a substrate etching effect supported by VUV radiation. For polymers coated without VUV irradiation, the deconvolution of the C1s peaks showed a significant decrease of CO bonds for both PI and PP substrates. 相似文献
4.
Owing to the rough warehouse handling of storage sacks in tropical areas in Africa, a suitable storage sack should not support de novo growth of fungal spores because this would reduce the tensile strength of the packaging material and act as a springboard for infecting grain contents. This paper reports the effect of activity of saprophytic fungi on the tensile strength of jute and woven polypropylene sacks. New woven polypropylene sacks carried lower levels of fungal spores (1.3×101 cfu/72 cm2) than jute sacks (3.0×103 cfu/72 cm2). The natural mould penetration and growth was examined on sections (4×5 cm) of both jute and woven polypropylene after previous incubation at relative humidities of 55, 60, 65, 70, 75, 80, 90 and 95% for 10 weeks by placing them on Sabouraud's Agar. There was a significant difference (P = 0.05 level of significance) between the higher penetration of mould growth on jute sacks and that obtained on woven polypropylene sacks. Saprophytic fungi (Aspergillus candidus, A. flavus, A. fumigatus, A. niger, A. japonicus, A. parasiticus, A. ustus, Fusarium oxysporium, F. moniliforme, Penicillium verucosum var. cyclopium, Rhizopus oryzae and Trichoderma viride) isolated from jute sacks reduced tensile strength, measured by an Instron Model 1026, by 50–75% after 10 weeks at 90% R.H. Same fungal species on woven polypropylene sacks did not alter the tensile strength. Woven polypropylene sacks did not absorb moisture whilst the moisture content of jute sacks increased by 5.3–6.0% in 10 weeks at 90% R.H. with concomitant increase in mould and yeast counts by 1–2 log cycles. Evidence is presented to show that there was a positive correlation between the final mycoflora on jute sacks and loss in tensile strength. No correlation, however, was found between the total aerobic bacteria on jute sacks and the concomitant reduction in tensile strength. Fungi therefore play a major role in the reduction of tensile strength of jute sacks. Sterilization by gamma irradiation (8.0 kGy) of jute and woven polypropylene sacks did not affect their intrinsic tensile strength. Woven polypropylene sacks therefore have many microbiological and physical advantages over the traditional jute sacks to merit their use for grain storage in tropical areas like Ghana. 相似文献
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6.
通过对热老化处理的聚内稀薄膜进行X射线衍射实验.对测得的实验数据采用X射线衍射线形分析理论处理,同时对热老化聚丙烯薄膜进行拉仲形变测量,得到材料的力学性质和微晶尺寸及内部点阵畸变的变化规律.从而将热老化聚丙烯材料宏观性质变化与微观结构联系起来,找出材料聚集态精细结构随老化时问而改变的微观规律. 相似文献
7.
丙烯酸接枝聚丙烯纤维的结构与性能 总被引:15,自引:2,他引:13
本文研究了用化学引发剂引发丙烯酸接枝聚丙烯纤维的某些影响因素。红外光谱分析表明,丙烯酸接枝在聚丙烯大分子链的叔碳原子上。X-射线衍射和DSC分析指出,纤维接枝后结晶度有所增加,接枝前纤维存在的β-变体转化成了α-变体,接枝纤维的吸湿性、离子交换容量和染色性随接枝率增加而增大。接枝纤维的力学性能有所下降。 相似文献
8.
本文简要介绍了费希尔-罗斯蒙特公司的POVOX系统特点,以及在间歇反应聚丙烯装置中的应用。 相似文献
9.
聚丙烯固相法接枝改性 总被引:3,自引:0,他引:3
聚丙烯固相法接枝不饱和单体是一种简便易行的本体法技术。与其它接枝方法相比,具有成本低、接枝率高、时间短、无溶剂回收、不妨害接枝物的进一步应用等优点。本文介绍了聚丙烯固相法接枝不饱和单体的进展,并较详细地讨论了影响接枝反应的各种因素。 相似文献
10.