Investigations of surface characterization of silicone rubber due to tracking phenomena under a.c. and d.c. voltages

In the present work, tracking phenomena has been studied with silicone rubber material under the a.c. and d.c. voltages following IEC-587 standards. The surface condition of the tracked zone was analysed using wide angle X-ray diffraction (WAXD) and thermogravimetric differential thermal analysis (TG-DTA) studies. The tracking time was different for a.c. and d.c. voltages.     

Investigations of surface degradation of high‐density polyethylene materials resulting from tracking,using physicochemical analysis

In the present work tracking phenomena were studied with high‐density polyethylene (HDPE) materials under dc voltage, with NH₄Cl and acid rain as contaminants. It was determined that the tracking time of the material depends on the conductivity and flow rate of the contaminant. Furthermore, physicochemical analysis by wide‐angle X‐ray diffraction studies, differential scanning calorimetry, and luminescence spectroscopy was carried out, whereupon it was concluded that the tracking process is a surface‐degradation process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2843–2849, 2002; DOI 10.1002/app.10260     

Isothermal crystallization of metallocene‐based propylene/α‐olefin copolymers

Isothermal crystallization and subsequent melting behavior of two propylene/hexene‐1 copolymers and two propylene/octene‐1 copolymers prepared with metallocene catalyst were investigated. It is found that γ‐modification is predominant in all copolymers. The Avrami exponent shows a weak dependency on comonomer content and comonomer type. At higher crystallization temperatures (T_c) the crystallization rate constant changes more rapidly with T_c and the crystallization half‐time substantially increases. Double melting peaks were also observed at high T_c, which is attributed to the inhomogeneous distribution of comonomer units along the polymer chains and the existence of crystals with different lamellar thicknesses. The equilibrium melting temperatures (T) of the copolymers were obtained by Hoffman–Weeks extrapolation. It was found that the T decreases with increasing comonomer content, but are independent of comonomer type, implying that comonomer units are excluded from the crystal lattice. Dilation of the crystal lattice was also observed, which depends on crystallization, comonomer content, and comonomer type. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 240–247, 2005     

Parameters governing strain induced crystallization in filled natural rubber

A series of in situ synchrotron X-ray diffraction experiments are performed during the stretching of weakly and highly vulcanized carbon black (CB), silica and grafted silica filled natural rubber sample (NR). Conversely to literature, Mullins effect observed after one stretching cycle modifies the strain induced crystallization (SIC) behaviour of the sample. The onset of crystallization is ruled by the strain amplification induced by the filler presence. Moreover, fillers (CB and silica) behave as additional crosslinks into NR network, through filler-rubber interactions that either accelerate or slow down the crystallization rate depending on NR matrix chemical crosslink density. This is consistent with the assumption that effective network density, which is due to chemical crosslinks, entanglements, and filler-rubber interactions, controls the crystallization rate.     

透明聚丙烯EP2X32G结晶性能研究

通过差示扫描量热仪和广角X光衍射等分析方法,研究EP2X32G及其基料的结晶性能。结果表明,EP2X32G及其基料中存在α和γ两种晶型。     

等离子体处理PET纤维表面形态结构的研究

用广角Ｘ射线衍射仪（ＷＡＸＤ）、扫描电子显微镜（ＳＥＭ）研究了经不同等离子体条件处理的ＰＥＴ纤维表面形态结构的变化。结果表明，随着功率增大、时间增长和压力增大，等离子对ＰＥＴ纤维刻蚀逐步加深，刻蚀作用由非晶区向晶区发展，结晶度亦随之增大，不同气体对ＰＥＴ纤维的刻蚀作用依次为氧气＞空气≈氩气＞氮气。     

Polypropylene/carbon nanotube nanocomposite fibers: Process–morphology–property relationships

This study is focused on aligning carbon nanotubes in polypropylene matrix by melt spinning. Two different weight percentages (0.5% and 1.0%) of nanotubes were used for the synthesis of the nanocomposite fibers. The effect of the nanotubes on the crystallization and mechanical behavior of polypropylene as well as the effect of draw ratio on the nanocomposite morphology and properties is also discussed. Correlation of fiber morphology and nanotube alignment was done using differential scanning calorimetry, wide‐angle X‐ray diffraction, and transmission electron microscopy. Significant improvement in tensile modulus and tensile strength were observed, which is characteristic of a highly aligned nanotube system. A substantial vincrease in the onset of decomposition was observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3844–3850, 2007     

聚苯胺晶性问题的探讨

用广角X射线衍射(WAXD),SEM,DSC和TGA方法研究了聚苯胺的晶性问题,结果表明,不同条件下所得聚苯胺其本征型的结晶行为差别较大。当聚合溶液的酸浓度在0.001～7N范围内时,随着酸浓度增加,其本征态聚合物的结晶性降低。所得产物的掺杂态较本征态更容易结晶,结晶度随掺杂剂浓度的升高而增加。适当的热处理可提高聚苯胺的结晶能力。     

A study of the crystalline transitions of polyamides X 18

The crystalline transition behavior of polyamides X 18, where X = 2, 4, 6, 8, 10 and 12, has been studied by variable‐temperature wide‐angle X‐ray diffraction (WAXD) and real‐time Fourier‐transform infrared (FTIR) spectroscopy. It was found that polyamides 2 18 and 4 18 undergo the Brill transition on heating for both the melt‐crystallized samples and the solution‐crystallized samples. For polyamide 6 18, the melt‐crystallized sample undergoes Brill transition before melting but the solution‐crystallized sample melts prior to the complete crystalline transition. Polyamides 8 18, 10 18 and 12 18 do not undergo the Brill transition perfectly in advance of melting for either melt‐crystallized or solution‐crystallized samples. Real‐time FTIR analysis of polyamides X 18 provided helpful information for understanding the mechanism of the crystalline transition. Copyright © 2004 Society of Chemical Industry     

涤纶的结构与性能在后加工过程中的变化

用ＷＡＸＤ法，ＤＳＣ法，密度法，声速法，ＹＧ－００１单纤维电子强力仪，研究了涤纶在后加工过程中结构和性能的变化，以及工艺条件对纤维结构和性能的影响。研究结果表明，涤纶的各结构参数在后加工过程中变化十分复杂，其结晶结构主要在二道牵伸工序形成，在紧张热定型工序结晶度最高。各工序温度对结晶度，晶粒尺寸等结构参数影响较大，尤其是二道牵伸温度直接影响纤维产品的结构和性能，因此，实际生产中，合理，准确地控制好