聚四氟乙烯主要成型制品及生产工艺

介绍了由聚四氟乙烯悬浮细粉、分散细粉和分散乳液成型的主要制品及其技术指标和生产工艺等     

分散聚四氟乙烯细粉发展动向

聚四氟乙烯(PTFE)树脂分为二类:一类是用悬浮聚合工艺制得的悬浮PTFE,粒径20～600μ,专供压缩成型用的模塑粉;另一类是用分散聚合工艺制得乳状分散液,经凝聚、干燥而成的分散PTFE,可供膏状挤出成型用的细粉。     

中华人民共和国国家标准 聚四氟乙烯材料命名

本标准规定了聚四氟乙烯材料的命名方法。该方法根据聚四氟乙烯树脂的聚合方法、加二方法,特征性能、添加剂种类及含量进行命名。本标准适用于分散法或悬浮法聚合的聚四氟乙烯树脂,包括共聚单休含量不大于1%的共聚物和加入添加剂的聚四氟乙烯树脂,但不包括聚四氟乙烯分散液。     

悬浮聚四氟乙烯的热解规律与产物表征

采用热红联用分析方法，研究了悬浮聚四氟乙烯（PTFE）细粉热解规律并对裂解产物进行了表征。结果表明：浙江巨圣和山东东岳公司的悬浮细粉具有相同的热稳定性，在590℃达到最大热失重速率；等温热解随温度升高而反应加快，反应级数在0．6—1．0之间；红外表征，升温和等温热解过程中的产物相同，主要成分都是四氟乙烯。     

国外分散聚四氟乙烯的发展

聚四氟乙烯具有悬浮法树脂,分散法树脂和浓缩分散液三种主要形式。分散法聚四氟乙烯是由分散聚合得到的分散液经凝聚、干燥而成。它具有直径0.2～0.5微米的初级粒子,凝聚后的次级粒子直径460～550微米虽然同样是聚四氟乙烯,但是与悬浮法树脂在物理性质和加工工艺上都有明显的差别。     

加工应用对我国氟树脂质量的要求

本文讨论了提高聚四氟乙烯悬浮树脂质量的具体要求。聚四氟乙烯塑料新产品的开发主要集中在分散树脂,指 出了加工膨体聚四氟乙烯、高压软管和涂层制品对树脂的不同要求。建议先开发FEP、PVDF、PFA三种热塑性氟树脂。     

1悬浮聚四氟乙烯品种的新系列

悬浮聚四氟乙烯的品种,随者新加工方法的发展,也不断地发展。五十年代初期,当悬浮聚四氟乙烯开始推向民用的时候,粉末和颖粒较粗,以后随应用上的需要,发展了一些颗粒较细的品种。同时,为了能够加工长度不限的型材,还定型生产一种经过予烧结的螺旋挤出和柱塞挤出加工用的粉料.所以茬五十年代末斯,悬浮聚四氟乙烯的     

我国聚四氟乙烯发展现状

聚四氟乙烯(PTFE)是氟塑料的主要品种，主要分为粗粒级、填料级、粉末级(絮粘分散)、水性分散级和石蜡级等，其耐热、耐化学品性能良好，摩擦系数低，电气绝缘性能十分优异，能在高温下连续使用。目前供应市场的PTFE三大品种分别为悬浮树脂、分散树脂和浓缩分散液，分别占消费量的50％-60％、20％-35％和15％-20％。     

中华人民共和国国家标准——聚四氟乙烯树脂粒度试验方法

本标准适用于悬浮或分散法聚合的聚四氟乙烯树脂粒度的测定,以平均粒径表示。1 定义对于一定质量的树脂,累积质量50%时,相对应粒子的直径 d_(50)。称为该树脂的平均粒径(?)。2 A 法:湿筛法适用于悬浮树脂和分散树脂的粒径测定。对于粒径小于100μm 聚四氟乙烯树脂,推荐按附录 A《65 μm 筛上保留数试验方法》进行。对于分散树脂粒度测定也可按附录 B《聚四氟乙烯树脂粒度的试验方法(干筛法)》进行。2.1 试验原理     

气流预分散对涡流空气分级机分级性能的影响

在物料进入涡流空气分级机前采用了气流预分散装置,使物料悬浮分散并输送到分级机中。以滑石粉和石灰石粉料为原料进行分级实验,研究不同条件下气流预分散对分级性能的影响。采用激光多普勒测速仪对分级机内环形区流场进行速度测定,分析预分散气流对流场的影响。结果表明,当预分散气速大于1.1 m/s时,细粉产率、牛顿分级效率和切割粒径随预分散气速的增大而增加;在不同的系统进口风速条件下,物料预分散后,细粉产率、牛顿分级效率增加;平均粒径小的石灰石粉料其中含有的超细颗粒(<4μm)不易实现气流预分散,预分散气流可以明显地减小对分级不利的轴向速度。     

聚四氟乙烯的加工成型技术

综述聚四氟乙烯（PTFE）的性能特点，以及不同品种PTFE（悬浮聚合PTFE、乳液聚合PTFE和PTFE分散乳液）成型制品所适用的成型工艺。介绍PTFE的模压成型，等压成型，挤压成型，流延成型，热真空成型、热压成型、热吹塑成型及缠绕成型等技术。     

Sorption and other properties of polytetrafluoroethylene/cellulose composite aerogels

Polytetrafluoroethylene/cellulose composite aerogels containing PTFE from 0 to 40 wt.% were obtained by drying the corresponding suspension mixtures at a temperature of 50°C. Cellulose isolated from the stem of Sosnowski hogweed was used as the main component of the aerogels. In present work, the composite aerogels were heated in an inert atmosphere at a temperature of 370°C to partially hydrophobize cellulose and remove surfactants that were present in the initial PTFE suspension. It was found that at this temperature, the thermal degradation of cellulose proceeded differently in the presence and absence of PTFE. The maximum water contact angle (156°) was obtained for the sample with 10 wt.% PTFE. Hydrophobized samples of aerogels were studied with the help of infrared spectroscopy, scanning electron microscopy, and powder x-ray diffractometry and tested as sorbents for various solvents. It was found that the volume of solvent absorbed by the aerogel, in the case of a sample with a PTFE content of 40 wt.%, can even exceed the initial volume of the absorber.     

膜裂切割法聚四氟乙烯纤维的制备及其力学性能

以不同聚四氟乙烯分散树脂为原料,通过混料、熟化、预成型、压延、双向拉伸及膜裂切割等工艺,制备了高性能聚四氟乙烯(PTFE)纤维.试验结果表明:树脂原料的优劣、热处理温度及拉伸工艺是影响PTFE纤维力学性能的主要因素,PTFE纤维的拉伸倍数应该控制在32～49之间,最佳的拉伸温度在240～320℃之间.     

Combustion synthesis of ultra-fine SiC powders in low pressure N2-atmosphere

Ultra fine SiC nano-powders (100–300 nm) of high purity were successfully produced by combustion of a powder mixture of Si and C, with the addition of poly-tetra-fluoro-ethylene (PTFE) as a chemical stimulator, in a moderately pressurized nitrogen atmosphere (1–10 MPa). The experimental results showed that with the aid of mechanical activation of the starting powders, a small amount of PTFE (1.5 wt%) can effectively stimulate the reaction between Si and C. Both the experimental results and thermodynamic calculations indicate that the formation of Si₃N₄ plays a key role in the process. The optimum conditions for producing the aforementioned SiC fine powders were 1.5 wt% PTFE, 1 MPa N₂ pressure and no addition of diluents of SiC powder.     

Formation mechanism of porous structure in polytetrafluoroethylene (PTFE) porous membrane through mechanical operations

Polymeric porous membranes were prepared from polytetrafluoroethylene (PTFE) fine powder by a series of mechanical operations, such as extrusion, rolling, and stretching. The structure of the prepared porous membrane was well characterized by a spatial periodicity of nodes (domain of agglomerated PTFE particles) and fibril domains. The fibrils were highly oriented in the direction of the stretching operation, providing pores in the polymeric membrane as slit-like voids between adjoining fibrils. The unit size of the periodic structure varied depending on the number averaged molecular weight of PTFE and the stretching conditions, the temperature of stretching, and the stretching rate and stretching ratio. A fibril consisted of several thread-like structures that were easily formed between PTFE particles due to the rolling operation in parallel with their direction. The dependence of the steady tensile stress in the stretching operation on the PTFE molecular weight was much weaker than that presumed for noncrystalline polymeric systems. The activation energy of 11.3 kJ/mol for the growth of fibrils was only several times as large as the thermal energy at the ambient temperature. These results imply that the thread-like structures can easily be pulled out of PTFE particles. This view is in accordance with the previously proposed microstructure in PTFE particles.     

Nonaqueous Spray-Drying as a Route to Ultrafine Ceramic Powders

Spray-drying imparts unique powder handling features to a wide variety of dried products and is usually carried out in a heated airstream while feeding an aqueous suspension of some solid material. The present work, however, explores nonaqueous spray-drying as a means of preparing fine powders of metal oxides. In this case an alcohol solvent was used in place of water and the slurry sprayed under an inert atmosphere. Using the nonaqueous technique, the product consists of distinct but loosely aggregated primary particles.     

新型微孔聚四氟乙烯密封板材的研制与应用

通过模压烧结工艺成功研制了一种微孔聚四氟乙烯密封板材,该密封板材具有良好的压缩回弹性能和抗蠕变松弛性能,其综合性能明显优于传统聚四氟乙烯密封材料,并达到了国际同类产品的先进水平,非常适合螺栓载荷较低、变形补偿要求较高的密封场合。     

聚四氟乙烯废料回收利用研究进展

介绍聚四氟乙烯(PTFE)废料回收利用的几种方法。其中机械法制得的再生PTFE粉可模压成型,也可作为填料或添加剂;辐射法制得的再生PTFE粉可与其它添加剂共混模压成型,或用作润滑剂和油墨等的添加剂、合成材料的改良剂等;热解PTFE可用于回收TFE、八氟环丁烷等工业原料或液体燃料,但需抑制有毒物质的产生。     

Strength development in powder processing of poly(tetrafluoroethylene)

Poly(tetrafluoroethylene) (PTFE) is a versatile engineering plastic with excellent chemical and electrical resistance, a wide working temperature range, and a low coefficient of friction. PTFE is processed by the powder processing technique because of its high melt viscosity. The powder processing of polymers involves cold compaction of the polymeric powders, followed by sintering of the preforms at elevated temperatures. Sintering is a critical operation since the mechanical properties of the products are determined by the interparticle coalescence and diffusion of polymer chains across the interface. The results of the studies of the strength development during sintering of PTFE are reported here. The strength was measured in terms of the tensile strength at break, and the dependence of the tensile strength on compaction pressure, particle size, and processing time is discussed. The time dependence of strength development could be described by a diffusion controlled process in which the strength is proportional to the 1/4th power of the processing time.