Synergistic regulation of current-carrying wear performance of resin matrix carbon brush composites with tungsten copper composite powder

Resin matrix carbon brush composites(RMCBCs)are critical materials for high-powered electric tools.However,effectively improving their wear resistance and heat dissipation remains a challenge.RMCBCs prepared with flake graphite powders that were evenly loaded with tungsten copper composite powder(RMCBCs-W@Cu)exhibited a low wear rate of 1.63 mm^(3)/h,exhibiting 48.6%reduction in the wear rate relative to RCMBCs without additives(RMCBCs-0).In addition,RMCBCs-W@Cu achieved a low friction coefficient of 0.243 and low electric spark grade.These findings indicate that tungsten copper composite powders provide particle reinforcement and generate a gradation effect for the epoxy resin(i.e.,connecting phase)in RMCBCs,which weakens the wear of RMCBCs caused by fatigue under a cyclic current-carrying wear.

Properties of a New Dental Photocurable Matrix Resin with Low Shrinkage

In order to reduce the amount of volumetric shrinkage that occurs in dental composites as a result of curing,a new kind of dental matrix resin combining bisphenol-S-bis（3-meth acry late-2-hydroxy propyl）ether（BisS-GMA） with the expanding monomer unsaturated spiro orthoesters 2-methylene-1,4,6-trispiro[4,4] nonane （SOE） was prepared,with triethylene glycol dimethacrylate （TEGDMA） as diluent.CQ （camphorquinone） of 1wt% and DMAEMA （2-（dimethylamino） ethyl meth acrylate） of 2wt% were used as photoinitiation system to initiate the copolymerization of the matrix resins.The performance including volumetric shrinkage,degree of conversion and condition of the ring-opening reaction of SOE,as well as curing time and the tensile bond strength were investigated respectively by the dilatometer,Fourier transfer infrared,the universal testing machine,and so on.The ring-opening polymerization of SOE occurred.Meanwhile,the obtain copolymers were crosslinked.The matrix resin containing BisS-GMA and SOE showed a reduced amount of volumetric shrinkage at 1.52%,which is a promising strategy for obtaining a polymer with a low amount of volumetric shrinkage.Furthermore,the other properties were not compromised.

Henkel Technologies and Products for China Aerospace

Epoxy structural adhesives and composites have been in use for many years for the construction of aerospace vehicles. Henkel provides many epoxy products. Many other resin systems have been evaluated and several, such as imide, phenolic and cyanate ester, have also achieved significant use. Henkel’s newly developed “Epsilon” chemistry demonstrates unique features that benefit application in aerospace structure that use adhesives and composites.

Properties of a New Dental Photocurable Resin based on the Expanding Monomer and Threecomponent Photoinitiator System

The purpose of this study was to use. a three-component photoinitiation system comprising 1wt% CQ （camphorquinone）, 2wt% DMAEMA （2-（dimethylamino） ethyl meth acrylate） and 2wt% ph^2I^＋PF6^- （diphenyliodonium hexafluorophosphate） to initiate the copolymerization of the matrix resins which combine bisphenol-S-bis （3-methacrylate-2-hydroxy propyl） ether （BisS-GMA） with the expanding monomer unsaturated spiro orthoesters 2-methylene-l,4,6-tdspiro[4,4] nonane （MTOSN）, for minimizing the volumetric shrinkage that generally occurs during polymerization. It was hypothesized that MTOSN would expand volumetrically during polymerization under the three-component photoinitiator system and further reductions in volumetric shrinkage would be obtained. The performance study which consists of degree of conversion and condition of the ring-opening reactions of MTOSN, volumetric shrinkage and mechanical properties including tensile bond strength, compressive strength and Vicker＇s hardness were carried out respectively by Fourier transfer infrared, the dilatometer and the universal testing machine. The results supported that the dental composites based on the expanding monomer and three-component photoinitiator system engendered a greater decrease of volumetric shrinkage and better mechanieal properties.

CHARACTERIZATION AND THERMAL STABILITY OF PMR POLYIMIDES USING 7-OXA-BICYCLO[2,2,l]HEPT-5-ENE-2,3-DICARBOXYLIC ANHYDRIDE AS END CAPS

An anhydride monomer containing ether oxide bridge, 7-oxa-bicyclo[2,2,1]hept-5-ene-2,3-dicarboxylic anhydride （ONA）, was successfully synthesized by Diels-Alder reaction of furan and maleic anhydride. The ONA was also studied as an end-cap for the polymerization of monomer reactant （PMR） type polyimides. Three molecular weight levels of the ONA end-capped PMR resins were evaluated. The effects of process conditions of these novel PMR resins on thermal and mechanical properties were investigated. It was demonstrated that the imidized prepolymers using the end-cap have good processability, and the cured polyimide specimens exhibited good thermal stability. The initial decomposition temperature, Td （ca. 580℃） and glass transition temperature, Tg （330℃） of the novel resin （PI-20）, prepared trader optimum process conditions, compare favorably with the Td （ca. 620℃） and Tg （ca. 348℃） of the state-of-the-art resin （PI＇-20）, respectively.

Damping of Ni–Mn–Ga epoxy resin composites

By combining the advantages of effcient damping and high mechanical properties,Ni-Mn-Ga particle composites have a very good prospect for applications in damping structure design.In this paper,a ferromagnetic shape memory alloy Ni-Mn-Ga composite is prepared.Ni-Mn-Ga particle/bisphenol-A epoxy composite cantilever beam vibration tests under a magnetic feld and without the magnetic feld are conducted to analyze the structural damping ratios n.Meanwhile,the damping characteristics of the Ni-Mn-Ga composite are studied through the axial loading-unloading method and the acoustic emission signals method.The damping coeffcient of the composite for different Ni-Mn-Ga volume fractions is obtained.The interface properties of the composite are discussed by micro examination and axial loading.The relationships between the damping of the composite and that of the component materials are discussed.The specifc damping capacity（SDC）and acoustic emission counts diagram of different specimens with different Ni-Mn-Ga volume fractions are analyzed.