Tribological behavior of the polyamide composite coating filled with different fillers under dry sliding

The polyamide (PA) composite coating filled with the particles of microsized MoS₂, microsized graphite, and nano‐Al₂O₃, respectively, were prepared by flame spraying. The friction and wear characteristics of the PA coating and composite coating filled with the varied content of filler under dry sliding against stainless steel were comparatively investigated using a block‐ring tester. The morphologies of the worn surfaces and transfer films on the counterpart steel ring were observed on a scanning electron microscope. The result showed that the addition of fillers to the composite coatings changed significantly the friction coefficient and wear rate of the coatings. The composite coatings filled with a low level content of fillers showed lower wear rate than did pure PA coating under dry sliding; especially the MoS₂/PA composite coating had the lowest wear rate among these composite coatings. The composite coatings with a high level content of fillers had higher wear rate than did pure PA coating, except of the Al₂O₃/PA composite coating. The bonding strengths between the polymer matrix and fillers changed with the content of the fillers, which accounted for the differences in the tribological properties of the composite coatings filled with the varied content fillers. On the other hand, the difference in the friction and wear behaviors of the composite coatings and pure coating were attributed to the difference in their worn surface morphologies and transfer film characteristics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

单向C/C复合材料的液相法制备及其显微结构

以沥青、沥青加焦炭粉和树脂加焦炭粉3种预浸料制备纤维预浸体，模压成型制备初坯体，然后用沥青液相法制备了3种单向C／C复合材料试样，对这些试样的密度、孔隙率和显微结构进行了测试和观察。在热压成型初坯体内，收缩微裂纹沿纤维轴向与外界相通，可被再浸渍填充，而孔洞则大多与外界隔绝，不能被再浸渍填充。添加焦炭粉作填料有利于C／C复合材料中纤维体积含量的控制、减少封闭气孔的形成，提高材料的密度。但焦炭粉末将扰乱基体层状结构组织，甚至使其出现紊乱状态。     

New printing inks with barrier performance for packaging applications: Design and investigation

Barrier properties of packaging materials against moisture and oxygen penetration are of high relevance. Enhanced protection of existing materials against weather conditions can be achieved by application of printed coatings. To improve barrier performance of packaging materials, new inks for obtaining printed coatings with a layered structure were developed and investigated. The proposed ink compositions for flexographic printing on paper substrates are based on an environmentally friendly acrylic binder and contain inorganic fillers with platelet particles incorporated in the polymer matrix. Coatings based on the developed printing inks demonstrate significantly decreased water vapour permeability compared to traditional polymer inks. The effect of decreased permeability was investigated considering inks rheological behaviour, the coating structure, mechanical properties, surface energy and water uptake for different ink formulations. The developed inks provide variable optical properties including coatings with a relatively high transparency. The development of the functional barrier inks contributes to saving natural resources by prolonging life performance of packaging materials and goods.     

半导体ZnTe/GaAs界面层错的高分辨显微分析

本项研究对经热壁外延（ＨＷＥ）生长在ＧａＡｓ基底上的ＺｎＴｅ进行分高分辨显微结构的观察，在ＺｎＴｅ／ＧａＡｓ界面上不仅存在着混合型全位错的扩展，而且首次发现类似螺旋位错分解的层错，并将其归结为原子在不全位错之后的堆积。     

Mineral filler reinforcement for commingled recycled‐plastic materials

Three types of mineral fillers, gypsum, wollastonite, and talc, were investigated for their ability to modify the mechanical properties of commingled recycled‐plastic composites containing 0.07–0.26 v/v of filler. Mechanical test results showed that the talc reinforced composites were significantly better in mechanical properties when compared with the gypsum and wollastonite composites. Scanning electron microscopy (SEM) showed that gypsum formed large agglomerates in the matrix. Interfacial adhesion between filler and matrix was evaluated using simple empirical models. To enhance the adhesion, talc, and wollastonite were pretreated with silane coupling agents, 3‐methacryloxypropyltrimethoxy silane (γ‐MPS) and 3‐aminopropyltriethoxy silane (γ‐APS). This did not result in any significant improvement to the material properties. The γ‐APS treatment, however, increased the tensile properties of the composites by ～ 5% when compared with the γ‐MPS treatment. The SEM investigations showed that the γ‐APS treatment provided better adhesion of filler particles and hence voids were less likely to form in the matrix when compared with the γ‐MPS composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

牙科光固化复合树脂材料的性能与展望

牙科光固化复合树脂具有色泽美观,强度高,临床操作方便,粘结固位效果好等优点,在牙科修复领域引起了广泛关注.该复合材料是由树脂基体、无机填料和光引发体系组成的,原料混合后经特定波长的可见光照射即可固化.牙科光固化复合树脂虽然已在临床上得到了应用,但在性能方面仍然存在某些不足之处,所以如何进一步提高其性能成为目前研究的热点之一.该文作者综述了树脂基体、无机填料和光引发剂的研究情况,对光固化复合树脂的力学性能、聚合度、吸水性和溶解性等性能及其影响因素进行了评述,并对今后的研究进行了展望.     

Thermal degradation and ageing behavior of microcomposites of natural rubber,carboxylated styrene butadiene rubber latices,and their blends

The effect of microfillers on the thermal stability of natural rubber (NR), carboxylated styrene butadiene rubber (XSBR) latices, and their 70/30 NR/XSBR blend were studied using thermogravimetric method. Microcomposites of XSBR and their blend were found to be thermally more stable than unfilled samples. The activation energy needed for the degradation of polymer chain was calculated from Coats‐Redfern plot. Activation energy needed for the thermal degradation of filled samples was higher than unfilled system. It indicated the improved thermal stability of the filled samples. The ageing resistance of the micro‐filled samples was evaluated from the mechanical properties of aged samples. The thermal ageing was carried out by keeping the samples in hot air oven for 7 days at 70°C. The mechanical properties such as tensile strength, modulus at 300% elongation, and strain at break were computed. As compared to unfilled samples, micron‐sized fillers reinforced systems exhibited higher ageing resistance. Finally, an investigation was made on the influence of ion‐beam irradiation on microcomposites of NR, XSBR latices, and their 70/30 blend systems using ²⁸Si⁸⁺ performed at 100 MeV. The surface changes of the samples after irradiation were analyzed using X‐ray photoelectron spectroscopy. The results of XPS measurements revealed that the host elements were redistributed without any change in binding energies of C_1s, O_1s, and Si_2p. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effects of the aluminum filler content on moisture diffusion into epoxy adhesives in distilled water and sea water

Epoxies are the most common of high‐performance structural adhesives, especially in automotive and aircraft manufacturing. In a variety of industrial applications, epoxy adhesives are required to have enhanced thermal conductivity. The normal method of changing this property is to add to the epoxy a filler of higher conductivity than the continuous phase. Although the improvement in the thermal properties of adhesives by the addition of metal fillers is obvious, their influence on water sorption characteristics of adhesives is not clear. It was the objective of this study to shed light on these aspects, which are lacking in the literature. The emphasis was placed on determining the moisture sorption behavior of aluminum‐powder‐filled epoxy adhesives under complete immersion in distilled water and sea water. Moisture diffusion tests show that the addition of aluminum filler into epoxy decreases the total amount of water intake at saturation in both fluids. However, there appears to be no significant effect of the aluminum filler content on the moisture diffusivity in epoxy adhesive specimens in either distilled water or seawater. It has also been determined that the adhesives adsorb a larger amount of water upon exposure to distilled water than when exposed to seawater, whereas the moisture diffusion rate in the adhesive immersed in seawater is higher than that in distilled water. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1165–1171, 2005     

Polypropylene/combinational inorganic filler micro‐/nanocomposites: Synergistic effects of micro‐/nanoscale combinational inorganic fillers on their mechanical properties

Polypropylene (PP) has wide applications in various areas, but its low‐temperature brittleness and low moduli have limited its applications in engineering areas. This article reported micro‐/nanoscale combinational inorganic fillers (CIFs) to reinforce PP‐matrix composites as the first example. The CIFs consisted of plate‐like talc (T), needle‐like wollastonite (W), and nano‐Al₂O₃ (N). The PP/CIFs specimens were fabricated via a process of twin‐screw extrusion and screw‐type injection molding. The mechanical properties and thermal deflection temperature (HDT) of the PP/CIF composites were tested according to the corresponding standards, and the morphologies of the tensile‐fractured sections were observed using FE‐SEM. The PP/WT composites had higher mechanical properties and HDTs than those of either PP/W or PP/T. Small amounts of Al₂O₃ nanocrystals together with WT simultaneously strengthened and toughened the PP‐matrix composites. The PP/WTN composite with 2.6% of nano‐Al₂O₃ had well‐balanced properties, enhanced by a large increment when compared with the PP matrix or PP/WT composites. The enhancements should be attributed to the synergistic effects of the CIFs not only in the aspect of various shapes (plate‐like, needle‐like, and spherical) but also in hierarchical size‐levels (microscale and nanoscale). The novel strategy overcame the limitation of conventional rigid modification and solved the problem of uniform dispersion of nanocrystals in polymer matrices. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Selective laser sintering of polyamide 12/potassium titanium whisker composites

The excellent performance of potassium titanium whiskers (PTWs) reinforced plastics has been recognized; however, because of their large length‐to‐diameter ratio, they have not been applied in selective laser sintering (SLS). This article reports a new method for preparing polyamide 12 (PA12)/PTWs composite (PPC) powders for applications in SLS that uses a dissolution–precipitation process. The characteristics of the powders were evaluated. The results indicated that when the PTWs content of the composites was low (<10 wt %), the shape of the powder became more regular, and the particle diameter distribution became narrower. The crystallinity of PPC was 13 wt % higher than that of PA12. The sintering characteristics and mechanical properties of PA12 powder, glass‐filled PA12 (GF–PA), and PPCs were compared. The results showed that the sintering characteristics of PPCs (10 or 20 wt % PTWs) were as good as those of PA12. The mechanical properties were greatly improved by PTWs. The maximum tensile strength, bending strength, and bending modulus of the composites containing 20 wt % PTW were 68.3 MPa, 110.9 MPa, and 2.83 GPa, respectively, and were much higher than those of PA12 and GF–PA. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010