聚四氟乙烯树脂细粒模压粉生产工艺改进

对超音速气流粉碎机用于聚四氟乙烯树脂模压细粉生产进行了初试，并对粉碎工艺进行了改进，探讨了超细粉碎的可行性。     

聚四氟乙烯成型加工新技术

介绍了聚四氟乙烯(PTFE)成型的特殊性,并对现有各种加工方法的优缺点进行了比较.为了弥补现有各种加工方法的不足,设计了新型聚四氟乙烯加工设备--柱塞冲压式挤出机,并阐述了它的加工工艺过程和成型原理.     

聚四氟乙烯复合材料与弹性体的组合应用

本文介绍了聚四氟乙烯复合材料的物理机械性能、摩擦磨损性能,由聚四氟乙烯复合材料与弹性体组合而成的 密封具有二者双重优点,密封效果好,摩擦阻力小,综合性能优良,简要介绍了组合密封在液压气动等方面的应用。     

An essential work of fracture study of the toughness of thermoset polyester coatings

The fracture toughness of a range of thermoset polyester paints with different cross-link densities has been studied, using the essential work of fracture (EWF) method. The glass transition temperature, T_g, of each of the materials was measured using differential scanning calorimetry, and found to lie between 8 and 46 °C. EWF tests were performed on the paint films at a range of temperatures around the measured glass transition temperature of each material. The essential work of fracture, w_e, at T_g was found to decrease with increasing cross-link density from around 20 kJ/m² at a cross-link density of 0.4 × 10⁻³ mol/cm³ to around 5 kJ/m² for cross-link densities of approximately 1 × 10⁻³ mol/cm³ or higher. A maximum in the essential work of fracture was observed at around T_g when w_e was plotted versus temperature, which could be attributed to the effect of an α-relaxation at a molecular level. The polyesters were found to be visco-elastic, and the applicability of the EWF test to the study of these visco-elastic thermoset materials is discussed.     

Evaluation of the tear properties of polyethylene blown films using the essential work of fracture concept

In the case of very thin materials such as blown films, the applied stress state in front of the crack tip is normally a plane stress condition, and the deformation around the crack tip due to the remote stress is very large. However, current standard test methods for quantifying the fracture toughness of thin films, such as the Elmendorf tear test, cannot explain or represent the tear characteristics accurately. The common way of interpreting the test results from the Elmendorf tear test is to develop an empirical correlation and then compare the average values. In this paper, essential work of fracture (EWF) tests for five commercial polyethylene (PE) blown films have been conducted, and the fundamentals of their tear properties based on fracture mechanics have been studied. The results from the EWF test are interpreted based on two important parameters, i.e., the essential work of fracture (W_e) and the non-essential work of fracture (W_p). Further, the relationship between these parameters and the current standard Elmendorf tear test is shown.     

Effects of molecular structure on the essential work of fracture of amorphous copolyesters at various deformation rates

The fracture behavior of amorphous copolyesters with different molecular structure was studied with double edge notched tensile loaded specimens (DENT) using the essential work of fracture (EWF) approach. Various deformation rates ranging from 1 to 1000 mm/min were employed. Amorphous poly(ethylene terephthalate) (aPET) exhibited considerably higher specific essential and non-essential work of fracture than the copolyesters containing either cyclohexylenedimethylene (aPET-C) or neopentyl glycols (aPET-N). At high deformation rates, ductile/brittle fracture transition was observed with aPET-C and aPET-N, while aPET always fractured in ductile mode within the entire deformation rate range. These phenomena were ascribed to the different molecular flexibility and entanglement density of the copolyesters. The specific EWF of the aPET as a function of deformation rate went through a minimum. The initial decrease in toughness was caused by the hampered segmental mobility due to the increased deformation rate. The subsequent increase in toughness was attributed to the adiabatic heating induced temperature rise in the process and plastic zones. Strain-induced crystallization of the aPET was observed at ν=500 and 1000 mm/min, which may also contribute to the increase of the specific EWF.     

The properties of poly(tetrafluoroethylene) (PTFE) in tension

Samples of DuPont 7A and 7C Teflon (PTFE, poly(tetrafluoroethylene)) were tested in tension at strain-rates between 2×10⁻⁴ and 0.1 s⁻¹ and temperatures between −50 and 150 °C. Additionally, using a Hopkinson bar, a temperature series was undertaken in tension between −50 and 23 °C at a strain rate of 800 s⁻¹. To investigate the small-strain response, strain gauges were used to measure axial and transverse strain allowing the Poisson ratio to be calculated. The effect of crystallinity was investigated using 7C material thermally processed to produce more amorphous material. As expected, the tensile mechanical properties of PTFE are significantly affected by strain-rate and temperature, but only to a limited extent by crystallinity. The Poisson ratio at small strains was found to differ in tension (≈0.36) and compression (≈0.46). Failure behavior and microstructure were correlated to temperature induced phase transitions.     

Comparison of fracture behavior of nylon 6 versus an amorphous polyamide toughened with maleated poly(ethylene-1-octene) elastomers

The fracture behavior of an amorphous polyamide (Zytel 330 from DuPont), a-PA, and nylon 6 toughened by maleated poly(ethylene-1-octene) elastomers are reported. The deformation mechanisms during fracture were verified by examining an arrested crack tip and the surrounding regions using transmission electron microscopy analysis. a-PA blends show higher levels of impact strength and lower ductile-brittle transition temperatures than nylon 6 blends. Fracture toughness, characterized by both linear elastic fracture mechanics techniques in terms of the critical strain energy release rate, G_IC, and the essential work of fracture methodology, i.e. the limiting specific fracture energy, u_o, and the dissipative energy density, u_d, using thick (6.35 mm) samples with sharp notches, depends on ligament length, rubber content, rubber particle size and test temperature. In general, a-PA blends show larger values of u_d than do nylon 6 blends while the opposite is seen for u_o. The amorphous polyamide shows a similar critical upper limit on rubber particle size, or interparticle distance, for toughening as the semi-crystalline nylon 6; thus, it is clear that the crystal morphology around the rubber particles must not be the dominant cause of this critical size scale. The deformation mechanisms involved include cavitation of rubber particles followed by some crazing and then massive shear yielding of the matrix.     

碳纤维填充聚四氟乙烯的性能及应用

本文介绍了碳纤维对其填充聚四氟乙烯复合材料的物理机械性能、摩擦磨损性能的影响，简要介绍了该复合材料在液压气动密封等方面的应用。     

Characterisation of injected EPBC plaques using the essential work of fracture (EWF) method

The influence of processing induced morphology, thickness and ethylene content (EC) of different ethylene-propylene block copolymers on fracture properties has been studied using the essential work of fracture (EWF) method. To analyse the influence of EC, four different materials were chosen with 0, 5.5, 7.8, and 8.4% in weight EC. Each material was injected in three different thicknesses (1, 2 and 3 mm). The resulting plaques were tested using the EWF method in both main orientations; the melt flow direction and transverse to melt flow direction. Different fracture behaviours have been observed, some of them preventing the applicability of the EWF method. Polarised light microscopy observations have revealed the existence of a skin/core structure, which is reduced with an increase in thickness and EC.     

耐高负压、高温四氟紧衬粘接防腐管道

本文概述了几种四氟衬里防腐管道的施工工艺,提出一种新型的可耐高负压、耐高温的四氟紧衬粘接防腐管道,并详述其衬里工艺过程和性能测试值。     

聚四氟乙烯的表面处理与粘接

本文介绍了聚四氟乙烯PTFE的表面处理方法、表面改性剂以及与聚四氟乙烯粘接性能优良的粘接剂     

The application of the essential work of fracture methodology to the plane strain fracture of ABS 3-point bend specimens

The applicability of the EWF methodology to 3-point bend (SEB) specimens under conditions other than plane stress has been assessed experimentally. Different fracture conditions, pure plane strain and plane strain/plane stress transition, were obtained by varying the specimen thickness and testing temperature (20 and 80 °C). Post-mortem fracture surfaces appeared always completely stress-whitened, indicating ductile fracture. The load-line displacement plots are similar over a well-defined range of ligament lengths for which the application of the EWF methodology was in principle possible. Nevertheless, in experiments conducted at room temperature, crack growth was observed to initiate before maximum load and complete ligament yielding. This behaviour was confirmed through plastic collapse analyses. A critical ligament length was found, over which the total specific work of fracture was dominated by edge effects. Below this critical ligament length, EWF methodology was still applicable and it was possible to extrapolate reliable w_Ie values.     

Plane stress fracture toughness of physically aged plasticized PETG as assessed by the essential work of fracture (EWF) method

The plane stress fracture toughness of amorphous copolyester (PETG) sheets plasticized by various amount of neopentylglycol dibenzoate (NPGDB in 0, 5, 10 and 20 wt%) was studied in as-received (AR) and rejuvenated (RJ) states by adopting the essential work of fracture (EWF) method. EWF tests were performed on deeply double-edge notched tensile loaded (DDEN-T) specimens at various deformation rates (2,10 and 100 mm/min) at room temperature. It was established that physical aging strongly affected the EWF terms. The specific yielding-related EWF increased with increasing deformation rate and decreased with increasing plasticizer content. The specific non-essential work and its necking-related constituent, which changed parallel to each other, remained constant up to 10 wt% NPGDB content and decreased afterwards. The plastic zone in the DDEN-T specimens was formed by cold drawing which is governed by the entanglement structure. This was demonstrated by the shape recovery of the plastic zone in the broken DDEN-T specimens after heating them above the T_g of the related PETG compound.     

Fracture of polybutylene terephthalate (PBT) film

Combined effects of thickness and temperature on essential work of fracture (EWF) of polybutylene terephthalate (PBT) film were studied using single edge notched tension (SENT) and double edge notched tension specimens. It is found that specific essential work of fracture (w_e) for PBT is independent of temperature below T_g (≈80 °C), but decreases above T_g. Between temperatures 25 and 100 °C, w_e was independent of film thickness in the range 0.125-0.375 mm. The specific non-essential work of fracture (βw_p) was temperature and thickness dependent, being greater for the SENT type specimens. Specimen orientation had no influence on w_e but strongly affected βw_p. It was found that βw_p is greater for cracks propagating normal to the extrusion direction as compared to the parallel direction.     

Thermal annealing as a new simple method for PTFE texturing

The present work demonstrates how polytetrafluoroethylene can be textured at both nanometric and microscopic scales by simply controlling the duration and temperature of the polymer annealing. Two main phenomena responsible for the PTFE surface texturing are identified which are the crystallite growth and the stress relaxation. The patterned surfaces were analysed by scanning electron microscopy, differential scanning calorimetry and contact angles measurements. As expected, an enhancement of the hydrophobic and oleophobic properties due to the texturation of the treated PTFE is observed.     

A quantitative analysis of the effect of interface delamination on the fracture behavior and toughness of multilayered propylene–ethylene copolymer/low density polyethylene films by the essential work of fracture (EWF)

The multilayered propylene–ethylene copolymer (CPP)/low density polyethylene (LDPE) composite sheets were prepared by the microlayered coextrusion system. The essential work of fracture (EWF) method was firstly used to quantitatively evaluate the fracture behavior of layered materials. The experimental results indicated that the two-dimensional layered interfaces in the multilayered materials could play an important role in the fracture behavior. The specific essential work of fracture, w_e, increased with the layers due to interfacial delamination. Additionally, the different testing speeds had a dual effect on the increscent trend of the specific essential work of fracture, w_e, with increasing layers.     

Fracture behaviour of polypropylene films at different temperatures: fractography and deformation mechanisms studied by SEM

The fracture surfaces and the deformation micro-mechanisms of one polypropylene homopolymer and three ethylene-propylene block copolymers (EPBC) have been studied by scanning electron microscopy. The results are compared to the essential work of fracture parameters obtained in a previous study with deeply double-edge-notched-tension samples of films fractured between −40 and 70 °C. The homopolymer shows shear-yielding at T≥−20 °C, but at lower T, crazing prevails. The EPBC display shear-yielding for T>0 °C, while a combination of cavitation and shear-yielding occurs at lower T, which is responsible for stress-whitening. The variations of the specific essential fracture work and specific plastic work with T and with ethylene content have been successfully explained in terms of the prevalent deformation mechanisms.     

基于仿生矿化的PTFE中空纤维膜亲水改性研究

由于聚四氟乙烯(PTFE)材料具有强疏水性和极低的表面能,使得PTFE中空纤维膜润湿性差,难以处理水性溶液,限制了其应用过程和领域,因此开展PTFE中空纤维膜亲水化改性研究具有重要的现实意义。利用仿生矿化技术对PTFE中空纤维膜进行表面改性,研究了不同矿化工艺对膜亲水性能的影响,并对改性前后PTFE中空纤维膜的官能团、水通量、气通量、孔径及孔径分布进行了表征。研究表明,仿生矿化能够提高PTFE中空纤维膜的亲水性和水通量,同时由于碳酸钙分子进入膜孔内部,使孔径分布更加均匀,平均孔径和气通量减小。     

聚四氟乙烯烧结成型的制备工艺

对聚四氟乙烯（PTFE）进行了压制试验和烧结试验,讨论了成型压力与试件的致密度、压缩强度以及压缩模量之间的关系,且对不同烧结工艺下试件的压缩强度进行了分析,得到较合适的成型压力和烧结工艺。结果表明：咖材料的压缩强度随压制压力的升高而减小,压缩模量随压制压力的升高而增加;闻的成型压力为27．5MPa,烧结温度380℃,保温时间4h。