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采用化学控制降解法调节聚丙烯的分子量和分子量分布,以控制纺丝线上的结晶,可明显降低聚丙烯纺丝温度,提高成丝质量和生产效率,产生显著的经济效益。作者曾提出用聚丙烯流动性能估算它的分子量及分子量分布的方法,同时还指出,模拟计算也是一种 相似文献
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研究了几种纤维素混合醚酯的制备及其高压静电场纺丝性能,分析了溶剂组成、溶液浓度、分子量、酯化基团对成纤性和纤维直径的影响。结果表明:在非均相条件下,经过碱化、醚化与酯化,得到不同结构的纤维素混合醚酯HPMCP、HPMCT与HPMCAS,均可实现静电纺丝;在甲醇/二氯甲烷=1∶4的溶剂体系中易得到表面光滑纤维;在溶剂组成一定条件下,溶液仅在一定浓度范围可纺,且浓度越低、纺丝电压越高,纺丝平均直径越小;当溶剂组成、溶液浓度一定时,分子量对其溶液纺丝的可纺性有直接影响,HPMCAS仅重均分子量达到7.2×104才能获得表面光滑纺丝纤维;在溶剂组成、溶液浓度和分子量一定的条件下,相邻酰基间距离越小,酸性越强,溶液电导率越大,丝越细。 相似文献
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采用DMSO/H2O混合溶剂法制备了5种不同分子量的PAN,并以PAN为原料,DMF为溶剂,配成纺丝溶液,通过高压静电纺丝技术制备超细纤维毡(UFFM)。研究表明,相同单体组成和浓度、相同反应条件情况下,通过聚合制备PAN,随着混合溶剂中水含量的增加,生成的PAN粘均分子量相应增加,其转化率也增加。聚合所得的不同分子量PAN的热重分析显示,随着PAN分子量的增加,热重曲线的剧烈失重区会越来越明显,剧烈失重区的失重率也呈增加的趋势;高压静电纺丝研究发现,PAN-4和PAN-5纺丝溶液由于分子量过高而不可纺;另外,研究还发现,较高的纺丝电压有利于纤维直径的减小,但相应的纺丝稳定性减小,导致纤维直径分布的离散度增加。 相似文献
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聚丙烯腈纳米纤维的再细化 总被引:12,自引:0,他引:12
通过电纺丝法研究了溶剂种类、溶液浓度、纺丝倾斜角、聚合物分子量对纳米纤维形态和直径的影响,寻找到最佳工艺条件,并得到了平均直径为20nm的超细纤维. 相似文献
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采用低温溶液缩聚的方法,在N-甲基吡咯烷酮(NMP)-氯化锂(LiCl)溶剂体系中引入了4,4’-二氨基二苯醚(4,4’-ODA)作为第三单体,与邻氯对苯二胺和对苯二甲酰氯(TPC)反应,得到可用于直接湿纺的共聚物纺丝溶液。将原液进行湿法纺丝,经水洗干燥后得到原丝,采用SEM和电子拉伸试验机表征纤维的结构与力学性能。研究结果表明,共缩聚后可以得到粘度高、分子量大、稳定性好的纺丝原液,通过湿法纺丝制得的纤维具有良好的取向度、结晶度和热性能。 相似文献
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聚丙烯熔体在剪切或应变应力作用下 ,分子链发生取向形成伸直链纤维晶 ,这些先取向形成的纤维晶成为其后结晶的晶核 .这种线形排列的特殊自晶核被称作排核 ( Row nuclei) [1] .排核诱导的结晶温度高于异相核和均相核 .折叠链片晶在排核上附生生长 ,形成具有柱状对称性的超分子结构 ,称为柱状晶 ( Cylindrite) [2 ,3] .聚合物的分子量 ,剪切温度和剪切速度等因素对柱状晶的生成有很大影响 [4 ,5] .本文选用不同级分的聚丙烯样品 ,利用高分子 (特别是取向结晶 )的记忆效应 [6,7] ,研究了剪切后薄膜试样在熔融重结晶过程中柱状晶的形成和发展… 相似文献
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Water-based polyurethane ionemers which have been successfully synthesized at our lab are demonstrated to be polypropylene glycol-based polyurethane ionomers by FT-IR spectra. For polyurethane ionomers prepared at a fixed ratio of NCO to OH as a function of ionic content, their viscosities are seen to be higher for polypropylene glycol with molecular weight of 1500 (triols) than for polypropylene glycol with molecular weight of 1000 (diols) or 2000 diols based polyurethane ionomers, as a result of strong intra ionic chain interaction. On the other hand, the viscosities due to strong inter chain interaction appear to be higher for polypropylene glycol with molecular weight of 1000 than for polypropylene glycol with molecular weight of 1500 or 2000-based polyurethane ionomers made at a fixed ionic content and under the variation of the ratio of NCO/OH. Like surfactant, poly-propylene glycolbased polyurethane ionomers present in water can substantially reduce the surface tension-of water. Thus, it may be considered as an ionomer-like surfactant. 相似文献
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Su Nee Tan Daniel Fornasiero Rossen Sedev John Ralston 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):307-315
The foam behaviour of low molecular weight polypropylene glycols (PPG) was investigated as a function of concentration and molecular weight (190–2000 g mol−1). For each polypropylene glycol, foam stability increases with concentration and passes through a maximum, beyond which foamability is suppressed as the solubility limit of the glycol is exceeded and droplets of glycol form. Light-scattering data as well as static and dynamic surface tension results provide the key information leading to these interpretations. A maximum in foamability was observed for the PPG molecules with increasing molecular weight (caused by a change in molecular conformation at the interface). This suppresses the Marangoni effect and leads to a decrease in foam stability. 相似文献
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Ademar B. Lugao Lucia Noda Elisabeth. C. L. Cardoso Beatriz Hustzler Shinichi Tokumoto Ana Nery F. Mendes 《Radiation Physics and Chemistry》2002,63(3-6):509-512
It is well known that polypropylene undergoes simultaneous crosslinking and degradation under irradiation. However, there are speculations regarding the formation of branching under special conditions. It is also well known that the melt-strength property of a polymer increases with molecular weight and with long-chain branching due to the increase in the entanglement level. This study was a contribution to the understanding of the following points: the role of molecular weight, the role of structural modifications on nucleation properties; the structural changes on polypropylene.
The results showed that degradation was the major reaction in the initial step of irradiation, however, the largely modified molecules concentrated in the high molecular weight fraction. The results also confirm that the branching formation is likely to occur. 相似文献
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This study shows that the elongational behaviour depends upon molecular weight and upon elongational rate. If the molecular weight is low, elongational viscosity reaches rapidly a steady value but, if the molecular weight is high, the viscosity (or the elongational stress) increases continuously with the time. These behaviours may be explained in comparison of the relaxation rate determined by shear rheology as the reciprocal relaxation time with the elongation rate ϵ. If the elongation rate is lower than the relaxation rate the polypropylene chains may relax and the elongational viscosity reaches a steady value with the time. For high fluidity polypropylene the range of elongation rates within of which the elongational viscosity is constant with time is very large. On the contrary, if the elongational rate is higher than relaxation rate the polypropylene chains undergo a continuous deformation and then the elongational viscosity increases with time. The range of elongational rates within of which the stress is constant is narrow for high-molecular-weight polypropylene. Furthermore, the elongational behaviour influences the chain orientation in the crystalline and amorphous phases of the fibres. If the polymer chains are quenched in a relaxed state the orientation is lowered as shown with high fluidity polypropylenes. On the contrary, if the chains are cooled in extended state their orientation may subsist during crystallisation and the orientation factors may reach high values as shown with high-molecular-weight polypropylene. 相似文献