双向拉伸聚氟乙烯薄膜的拉伸工艺研究

探讨了聚氟乙烯(PVF)流延膜在制备过程中常见的缺陷及产生原因,并给出了具体的加工工艺参数。结合PVF 薄膜的双向拉伸机理,通过力学及热性能测试表明:膜片的纵向拉伸温度为120～135℃,拉伸比为2.5～3.0时,薄膜不会出现细颈现象,且所需拉伸应力较小;当横向拉伸温度控制在130～150℃,拉伸比为2.5～3.5时,薄膜厚度介于23～28μm之间,且力学性能基本保持各向同性;双向拉伸的薄膜经过170～180℃热定型之后,横、纵向收缩率均小于2%,具有良好的尺寸稳定性。

用于民用航空的聚氟乙烯薄膜研究

采用二次拉伸工艺制备了国产聚氟乙烯薄膜,对0.025mm典型厚度规格薄膜进行全面性能测试,并与相应的国外成熟材料进行对比。结果表明,国产聚氟乙烯薄膜纵向拉伸强度为66MPa,伸长率为121%,满足民用飞机使用需求,但略低于相应的国外成熟材料。对比两种聚氟乙烯薄膜在不同浸泡条件下的老化性能发现,国产聚氟乙烯薄膜MD拉伸强度变化率为2%~12%,与国外成熟材料相当。热老化后,国产聚氟乙烯薄膜MD拉伸强度下降了36%,相对国外材料较高,需要进一步改善。国产聚氟乙烯薄膜已满足民用飞机的装机要求,有望取代相应的国外成熟材料应用于民用飞机上,推进民机材料的国产化。

抗火焰传播包覆材料热封及阻燃性能研究

聚氟乙烯(PVF)具有优异的耐腐蚀、疏水和耐磨性能。Lamaguard和Terul系列产品是以聚氟乙烯面层复合纤维网格布及其他功能层制备得到的薄膜材料,可以作为空客、波音等民航客机的隔热材料包覆层使用。为了研究货架产品性能,采用T型剥离试验研究了面密度分别为38、34、33 g/cm^(2)的Lamaguard 400A、Lamaguard 401A和Terul 18H三种材料热封强度与热封温度的关系,确定了Lamaguard 400A和Terul 18H热封工艺参数(140℃×350 kPa×1.5 s),Lamaguard 401A在相同工艺参数横向包封强度最高仅约400 N/m,相较而言更适合缝纫或胶合等装配形式。通过开展材料基础性能、耐火阻燃性能和耐环境性能研究,比较了三种货架产品性能,并采用临界辐射通量试验,验证了包覆材料在模拟火场条件下的抗火焰传播性能,为材料选材和应用提供了数据支撑。研究发现,三种材料在燃烧试验中不产生明火,离火后无续燃,均具有优异的抗火焰传播性能。基础性能方面,面密度最高的Lamaguard 400A爆破强度最高,为260 kPa,且热封强度可达1200 N/m。Terul 18H面密度最低但水蒸气渗透率(0.47 perms)最高,超过Lamaguard系列材料约50%。Lamaguard 401A具有与Terul 18H相近的面密度,但纤维剥离强度低(横向85.92 N/m)、且热封强度低,不适用于具有高热封强度需求的应用环境中。

不锈钢地铁车辆侧墙内板成形模拟研究

以某型号地铁车辆不锈钢车体侧墙内板为例,利用Autoform有限元软件,分析了润滑方式、拉延筋、压边力和模具间隙等对不锈钢侧墙内板拉延成形的影响规律。结果表明:聚氟乙烯薄膜作为润滑介质垫在不锈钢板与凸凹模、压料板之间,能够显著改善侧墙内板的成形性,改善拉裂缺陷。通过正交试验得到匹配参数的优化组合,可进一步对拉延不足和拉裂缺陷协调控制。优化组合的参数设置为:拉延筋系数0.35、压边力300 kN和单边模具间隙1.20 mm。基于该模拟优化参数进行了模具设计和成形试验,得到了合格的试验件,验证了模拟仿真结果的准确性和控制措施的有效性。

Antimicrobial Expanded Polytetrafluoroethylene Film Prepared by 3-ray Radiation Induced Grafting of Poly（acrylic acid）

The simultaneous γ-ray-radiation-induced grafting polymerization of acrylic acid on ex- panded polytetrafluoroethylene （ePTFE） film was investigated. It was found that the degree of grafting （DG） of poly（acrylic acid） （PAA） can be controlled by the monomer concentration, absorbed dose, and dose rate under an optimal inhibitor concentration of [Fe2＋]=18 mmol/L. SEM observation showed that the macroporous structure in ePTFE films would be covered gradually with the increase of the DG of PAA. The prepared ePTFE-g-PAA film was im- mersed in a neutral silver nitrate solution to fabricate an ePTFE-g-PAA/Ag hybrid film after the addition of NaBH4 as a reduction agent of Ag＋ to Ag atom. SEM, XRD, and XPS results proved that Ag nanoparticles with a size of several tens of nanometers to 100 nanometers were in situ immobilized on ePTFE film. The loading capacity of Ag nanoparticles could be tuned by the DG of PAA, and determined by thermal gravimetric analysis. The quart- titative antibacterial activity of the obtained ePTFE-g-PAA/Ag hybrid films was measured using counting plate method. It can kill all the Escherichia coli in the suspension in 1 h. Moreover, this excellent antibacterial activity can last at least for 4 h. This work provides a facile and practical way to make ePTFE meet the demanding antimicrobial requirement in more and more practical application areas.

Low-Temperature Plasma Induced Grafting of 2-Methacryloyloxyethyl Phosphorylcholine onto Poly(tetrafluoroethylene) Films

Modification of poly(tetrafluoroethylene)(PTFE) films with 2-methacryloyloxyethyl phosphorylcholine(MPC) was performed by low-temperature plasma treatment and grafting polymerization.Surface properties of PTFE were characterized by attenuated total reflectance Fourier transform infrared(ATR-FTIR) spectra,X-ray photoelectron spectroscopy(XPS) ,and static contact angle.The results show that MPC has been grafted onto PTFE film surface successfully.Contact angle for the modified PTFE films in the water decreased from 108°to 58.25°,while surface energy increased from 17.52 mN/m to 45.47 mN/m.The effects of plasma treatment time,monomer concentration and grafting time on degree of grafting were determined.In the meanwhile,blood compatibility of the PTFE films was studied by checking thrombogenic time of blood plasma.

Structure and Properties of Polytetrafluorethylene and Polyurethane Layered Membrane for Protective Clothing

This paper presents a new idea for intensifying protective and stretch recovery properties of micro porous polytetrafluorethylene and hydrophilic polyurethane (PTFE/PU) layered membrane through a co-stretching process. The structure and properties of co-stretching PTFE/PU layered membrane and coated PTFE/PU layered membrane by means of directly coating the PU on the PTFE membrane were investigated using Electron Microscope, Universal Materials Testing Machine, and the water vapor permeability (WVP) was measured according to absorption method of water vapor of GB/T 12704-91. Contrasted to PU coating process, the PU membrane on the co-stretching PTFE/PU membrane is nonporous because of heat treatment process, which can prevent the SARS virus from permeating the Co-stretching PTFE/PU membrane. The stretch and recovery properties of the Co-stretching PTFE/PU membrane is at least 66% after being stretched to 50% of its original length in transverse directions and that of the coated PTFE/PU membrane is 52%. The WVP of the Co-stretching PTFE/PU membrane is 13 523 g/24 h·m^2. The results suggest that when Co-stretching PTFE/PU membrane is laminated to a stretchable fabric, the fabric would have excellent stretch and recovery properties while waterproof and being permeable to water vapor. So, the Co-stretching PTFE/PU membrane laminated fabric will be a comfortable protective clothing material.

Photolyses of mammalian carboxy-hemoglobin studied by photoacoustic calorimetry

The enthalpy and conformational volume changes in the photolyses of carboxy-hemoglobin (HbCO) of human, bovine, pig, horse and rabbit are investigated by photoacoustic calorimetry. Considering the time scales of the exciting laser pulse and the receiving ultrasound transducers (PVDF films and PZT ceramics), as well as the reaction lifetimes in the photolysis processes of HbCO, the measured results are related to the geminate recombination and tertiary relaxation in photolyses of HbCO. Moreover, the quantum yields of the five mammals are also measured by laser pump-probe technique. The results show that the dynamic parameters, such as enthalpy and conformational volume changes, differ between the processes of the geminate recombination and tertiary relaxation. Also, the dynamic parameters differ among the five mammals although some of them may be consistent with each other.