Processability of a metallocene‐catalyzed linear PE improved by blending with a small amount of UHMWPE

The processability of a metallocene‐catalyzed polyethylene blended in the melt with low amounts of ultra‐high molecular weight polyethylene was evaluated. Our morphological and thermal studies revealed that the blends were structurally heterogeneous, formed by a matrix of metallocene polyethylene and homogeneously distributed particles of ultra‐high molecular weight material. The visible particles were smaller than those of the reactor powder. Also observed was some degree of interaction between both phases. Rheological data indicated an intense effect of morphology on viscoelastic functions, beyond that expected for a system composed of noninteractive phases. Collectively, our findings suggest the existence, to some extent, of a homogeneous phase at the molecular level composed of a fraction of ultra‐high molecular weight species and metallocene polyethylene. This gives rise to a striking behavior during processing in that the blends show improved extrusion performance the higher their ultra‐high molecular weight polyethylene content. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2963–2971, 2005     

Irreversible formation of a network during melting/dissolution of nascent PE

A high temperature endotherm has been reported recently for PE samples during a slow T ramp which has been associated with a phase change in strained chains. From comparison of NMR and calorimetric data on nascent and melt/recrystallized samples, the following origin of the strain is now proposed. Nascent PE is a homogeneous material which contains a sizeable proportion of short-range ordered chains interrupted by loose knots. Due to expansion during melting, the knots become tighter and a physical network which encompasses a fraction of the chains is produced. The network so formed interrupts the melting process in the ordered chains. In PE and other polyolefins, melting resumes at higher T. The high T endotherms of physical and chemical networks are compared. The consequences of this network for polymer properties as well as its general occurrence are discussed briefly. © 1993 John Wiley & Sons, Inc.     

Ion Implantation on Ultra High Molecular Weight Polyethylene (Uhmwpe) for Medical Prosthesis

In order to improve the wear resistance of ultra high molecular weight polyethylene (UHMWPE), a surface modification is induced by ion implantation of different ions at 300 keV energy with doses ranging between 10¹⁴ -10¹⁷ ions/cm². Wear measurements, in terms of weight loss, are performed with a “pin on disc” friction machine; these tests measure the wear properly of the UHMWPE against a metallic probe before and after the ion implantation treatment. Results demonstrate that in the implanted samples the wear resistance increases by about 76% with respect to the non-irradiated samples. The irradiated polymeric layer was characterized with the mass quadrupole spectrometry, Raman spectroscopy, infrared absorption analysis, scanning electron microscopy, atomic force microscopy and calorimetric analysis. The results suggest that wear decrease effect can be attributed to the ion bombardment inducing a high carbon surface concentration and cross-linking effects in the irradiated polymeric layer. The irradiated UHMWPE surfaces find special applications in the field of the mobile prosthesis such as hip joints.     

Measurements of gas desorption from polyethylene-UHMWPE irradiated by 5 MeV electrons

Gas desorption in vacuum from electron irradiated ultra high molecular weight polyethylene (PE) is measured with a high sensible mass quadrupole spectrometer. Measurements are performed in thick PE irradiated with 5 MeV electron beams at doses of the order of tens of kGy. The irradiation modifies the PE molecules producing dehydrogenation, emission of different C _x –H _y groups, C-enrichment and carbon cross-linking processes. Results indicate that the radiation damage depends on the dose and that a significant change of chemical and physical polymer properties is reached for a critical dose of 18 kGy.     

Thermal and Mechanical Properties of Ultra High Molecular Weight Polyethylene Fiber Reinforced High-Density Polyethylene Homocomposites: Effect of Processing Condition and Nanoclay Addition

A new method to prepare single-polymer high-density (HDPE)-ultra high molecular weight polyethylene (UHMWPE) fiber (PE-PE homocomposites) composed and also PE-PE homocomposites containing HDPE organo montmorillonite clay (OMMT) nanocomposites as a matrix (PE nanohomocomposites) was used. Owing to the major importance of fiber impregnation by the matrix and its effect on the adhesion of matrix/fiber and, consequently, the mechanical properties of the composite, a combination of powder impregnation and film stacking methods, utilizing compression molding, were used for manufacturing the PE-PE homocomposites and PE nanohomocomposites. In addition, PE nanohomocomposites with the matrix containing different amounts of nanoclay were prepared to investigate the effect of the clay on the interfacial and mechanical properties of the PE-PE nanohomocomposites. Several different processing conditions were examined to determine the best conditions for manufacturing of the PE-PE homocomposite and PE nanohomocomposites and it was concluded that 40 bar and 10 min of compression molding resulted in the highest overall mechanical properties. The PE-PE homocomposites and PE-PE nanohomocomposites showed identical trends for the relationship between the effects of processing conditions and mechanical properties. Mechanical results demonstrated that clay platelets could increase the interfacial strength by improving physical entanglements between fiber and matrix through better cocrystallization.     

Correlations between the electric charging properties and the optically determined structure of non-woven fabrics

The aim of this paper is to determine the degree of correlation between the electrostatic potential distribution on the surface of non-woven fabrics and the material structure as obtained by optical means. The potential distribution on the material surface was monitored for several samples of two types of fabrics that were electrically charged using corona discharge. The results show that the charge distribution on the samples surface significantly correlates with the spreading and the third centered moment of the gray-scale pictures of the samples.     

Optimization of UHMWPE/graphene nanocomposite preparation by single‐supported Ziegler‐Natta catalytic system via RSM

In this study, the preparation of ultra‐high molecular weight polyethylene/graphene nanocomposite was carried out using single‐supported Ziegler‐Natta catalyst, and the operational conditions were optimized via response surface methodology. For this purpose, the effect of 3 parameters, monomer pressure, temperature, and molar ratio of [Al] respect to [Ti] on the catalyst productivity and molecular weight of the synthesized nanocomposite polymer, was investigated using the Box‐Behnken experimental design at 3 levels. Monomer pressure, temperature, and molar ratio of [Al] respect to [Ti] were considered as independent variables and catalyst productivity and molecular weight as dependent variables. The highest catalyst productivity and molecular weight were equal to 923 (grPE/mmolTi.h) and 2.04 (million gr/mol), respectively, which were obtained under optimal reaction conditions: temperature of 60°C, pressure of 8 bar, and molar ratio of 185. Finally, in order to investigate the morphology and nanoparticle dispersion in polymer matrix, scanning electron microscope and X‐ray diffraction were used. The results indicate the homogenous dispersion of graphene nanoparticles in polymer matrix.     

铝镧共掺杂的氧化锌红外隐身涂料在帐篷织物上的应用

以水性聚氨酯为粘合剂,掺杂Al和La的ZnO为填料,配以其它助剂制成了红外隐身涂料,应用在帐篷织物表面,探究涂层厚度以及填料含量对红外发射率的影响,并研究了导热系数和红外隐身性能之间的关系。 研究发现,涂层厚度和填料含量对涂层织物的红外发射率有着显著的影响。 当填料质量分数为70%时,得到的帐篷涂层织物的红外发射率可降至0.622,调节填料含量和涂层厚度,可以的得到红外发射率在0.622~0.932之间的帐篷涂层织物。 此外,发现导热系数对红外隐身性能也有一定的影响,红外隐身性能随着导热系数的增加而提高。 通过调节填料含量和涂层厚度制作不同红外发射率的涂层帐篷织物,放在不同背景下拍摄红外热成像图,发现涂层在不同的环境中均具有良好的伪装能力。     

织物表面摩擦特性测试装置及试验研究

为了评价织物表面的摩擦特性,表征织物和皮肤接触过程中摩擦力的动态变化信息,研制了一种能测试织物表面动态摩擦特性的机械测试装置,该装置集成了机械装置、传感器及控制系统,能一次性测试织物的静、动摩擦系数.基于测试过程中采集的原始数据,定义了摩擦功、静摩擦系数及动摩擦系数3个指标来评价织物表面的摩擦特性.试验采用12种典型的织物样本,对织物的表面摩擦特性进行了客观测试及主观评价,并在日本Kawabata KES-FB4系统上进行了对比试验.结果表明:针对12种典型的织物样本,3个评价指标均存在着显著的差异,牛仔布具有最大的静摩擦系数,经编网眼针织布具有最小的静摩擦系数,与常理相符.客观测试得到的动态指标摩擦功和主观评价的结果具有一致性.本测试装置得到的动态摩擦系数和KES-FB4测试得到的平均摩擦系数也具有一致性.该测试装置可以为相关领域的研究提供一种新的测试手段.     

Preparation of nonwoven polyimide/silica hybrid nanofiberous fabrics by combining electrospinning and controlled in situ sol-gel techniques

A controlled in situ sol-gel synthesis combined with the electrospinning technique and postspun imidization was applied in the fabrication of polyimide/silica hybrid nonwoven nanofiberous fabrics with excellent thermal and mechanical performance. The nanofiberous fabrics were prepared by electrospinning of the solution of tetraethoxysilane (TEOS) and polyamic acid (PAA). The different silica contents in the fabrics were achieved by varying the amount of TEOS while fitting the solid content of PAA. The final polyimide/silica fabrics was obtained after imidization of PAA and gelation of silica phase simultaneously accomplished through a step-wise heating process. Some specific IR techniques and other characterizations indicated the successful incorporation of the silicon dioxide (SiO₂) into the PI matrix and the relatively even distribution of the SiO₂ in the fabrics. An increase of 133 °C in the decomposition temperature and 4-fold enhancement of the ultimate tensile strength were achieved for the hybrids with a 6.58 wt.% of SiO₂ content, compared to the pure PI fabric. The excellent performance could be attributed to the good compatibility between the polyimide and silica, and good adhesion among the fibers, which resulted from the controlled TEOS hydrolysis and the simultaneous imidization and gelation process.