Yafei Lu

Development of eco-friendly brake friction composites containing flax fibers

Eco-friendly brake friction composites with good friction performance were developed. The raw materials utilized were selected according to eco-friendly criterion that natural products should be preferably chosen. The formulations are composed of plant flax fiber, mineral basalt fiber, and wollastonite as reinforcements, natural graphite as solid lubricant, zircon as abrasive, vermiculite and baryte as functional and space fillers, and cardanol-based benzoxazine-toughened phenolic resin as binder. To isolate the flax fibers, chemical and physical methods including drying, room temperature alkaline solution, and acid steam treatment were performed and fibers with micro-fibrillated structure on the surface were formed. A new cardanol-based benzoxazine synthesized by the reactions among cardanol, aniline, and formaldehyde was used as toughening for phenolic resin. The effects of both the content of treated flax fibers and friction temperature on friction performance, friction coefficient and specific wear rate, of the friction composites were evaluated by the extension evaluation method.

Synthesis and characterization of carborane bisphenol resol phenolic resins with ultrahigh char yield

Two carborane-containing resol phenolic resins (P1 and P2) with high boron content were synthesized via the reaction of carborane bisphenols (1 and 2) with formaldehyde in the presence of alkaline. HRMS results indicate that P1 is mainly composed of hydroxymethylated o-carborane bisphenols, the Mw of which was restrained around 500 due to the strong steric hindrance of o-carborane bisphenol. In contrast, the molecular weight of P2 was well regulated under various reaction conditions. The obtained resins were characterized with spectroscopic techniques including FTIR, 1H-NMR, 13C-NMR, and 11B-NMR, which gave satisfactory results. TGA studies show that P2 shows char yield of 88.9% and 92.9% at 900 °C under nitrogen and air respectively. The imported carborane cage endows phenolic resin with ultrahigh char yield. Particularly, the char yield of the obtained carborane-containing phenolic resin under air is higher than that under nitrogen. FTIR and XRD confirm that the carborane cage could react with oxygen to form B2O3 at elevated temperatures, which postpones the thermal decomposition of phenolic resin and accounts for the high char yield.

Synthesis, Characterization, Curing and Properties of Carboxyl-Terminated Liquid Fluoropolymers

Low molecular weight carboxyl-terminated liquid fluoropolymers with M n ranged from 2300 to 8000 were prepared by oxidative degradation of VDF-HFP copolymer. The factors to control M n of liquid fluoropolymers are types and contents of alkaline and oxidants. FTIR, 1H NMR, 19F NMR, 13C NMR and GPC were used to characterize the structure and M n of the liquid fluoropolymers. The cure reaction and properties of the carboxyl-terminated liquid fluoropolymers with epoxy resin were discussed. Thermal properties including thermal stability and T g of these cured fluoropolymer films were also examined. Cured films have good hydrophobic and oleophobic properties, as well as good chemical resistance.

Effects of walnut shells on friction and wear performance of eco-friendly brake friction composites

The paper addresses utilization of 0–14.6 vol.% alkaline-treated walnut shell powders (WSPs) as a functional filler in the proposed eco-friendly brake friction materials. Five non-asbestos friction material samples containing WSP and jute fibers from biomass as biodegradable components were prepared, also including several from natural resources, such as wollastonite, basalt fibers, zircon, barite, and vermiculite. The friction-wear properties of the prepared composites were tested by using Chase friction performance testing device. Furthermore, an extension evaluation method was introduced to rank the composites based on their overall friction-wear characteristics. The coefficient of friction (COF) and wear rate of the samples could be effectively improved, especially for the sample with a WSP content ≤5.6 vol.%. With confirmation of the analysis and characterization results, chars were very possibly formed by the degradation of organic ingredients, such as WSP and jute fibers, which played a key role in affecting the friction performance of the friction composites.

Synthesis, characterization and thermal stability of novel carborane-containing epoxy novolacs

Carborane bisphenol novolacs (3 and 4) were synthesized in the presence of acid catalyst from carborane bisphenols (5 and 6) and formaldehyde. Further epoxidization of carborane bisphenol novolacs with epichlorohydrin gave carborane bisphenol epoxy novolacs (1 and 2). The molecular weight and epoxy value of obtained resins were determined using the molecular weight of their precursors. The epoxy values of 1 and 2 were 0.48 and 0.52 respectively, higher than the maximum theoretical epoxy value (0.45) of difunctional carborane bisphenol epoxy resins. FTIR and NMR were utilized to characterize 1 and 2. The curing behaviors were also studied by DSC and the optimized curing conditions were obtained. TGA analysis indicated that carborane moiety could shield its adjacent organic structures against initial decomposition. On the other hand, B―H on carborane cage could react with oxygen to form a three-dimensional network linked by B―O―B and B―C bonds, which further blocked the movement of formed radicals and thus the degradation process was inhibited.

Structure and properties of kaolinite intercalated with potassium acetate and their nanocomposites with polyamide 1010

The intercalation complex marked as KAA was a modified kaolinite (KA) with potassium acetate as an intercalating agent, which was used as a reinforcement to prepare polyamide 1010 (PA1010) matrix nanocomposites (PKAA) by melt compounding. X-Ray diffraction results indicated that the interlayer basal spacing increased from 0.720 nm (KA) to 1.411 nm (KAA), after an intercalation process with an intercalation ratio of 99.7%. The nanocomposite with 2 wt% KAA exhibited the best comprehensive mechanical properties, including tensile strength, elongation at break, and notched impact strength. Furthermore, the thermal performance of these nanocomposites could be effectively improved, which manifested as the elevated glass transition temperature and thermal decomposition temperature in the test results of the dynamic mechanical thermal analysis and thermogravimetric analysis (TGA). The melting point and crystallization behavior of PKAA were also increased due to results from the differential scanning calorimetry. Besides, the bilayer inserting model was simulated by Materials Studios software to further understand the structure-function relationship of PKAA.

Friction Modifiers Optimization of the Ceramic Composites for Automotive Applications

We decided to focus on ceramic-type of friction composites, in which the effect of selected components on the friction performance was investigated. To find the options for one component to play dual role in friction performance, interest was put to the clay minerals, in our case phyllosilicate — vermiculite. Vermiculite was used as original or as modified material and added to the composition in several volume fractions to observe the gradual friction performance changes. The modification of the vermiculite. comprised of chemical, physical and mechanical methods, aimed at multifunctional properties in composite. Vermiculite was jet milled alone and with polymeric powder, thermally treated, which gave an option to observe, whether such modification is useful for friction performance improvement. Friction surface changes versus friction performance were evaluated.

Simulation of Friction Composite Behavior Using Heat Treatment

One of the factors influencing performance of friction composites is stability (optimal condition ) of surface at high temperatures. When measuring coefficient of kinetic friction and volume wear rate, preheating of tiie cast iron disc is used to simulate behaviour in real conditions. Using this method the comparison of different friction composites can be canied out. The heat treatment of selected samples in inert atmosphere was applied to obtain information about tiie bulk material and surface changes at gradually increased temperature. We have observed changes in components morphology and phase composition of bulk material and compared it with structure of surface after friction test. We have focused on characterization of friction modifiers, fibrous fillers and resin binder as well.

Effect of Particles Size and Morphology of Selected Compounds of Friction Composite on Friction Performance

Friction materials are multicomponent composites, where is very important to maintain homogeneity of material, which can be assured using an adequate components with optimal particle size. Friction components can be produced using techniques which not always prioritize to achieve the homogeneity of final friction composite. For that reason we used special preparation technique to produce the particles with nearly identical shape - the jet milling technique. This technique is a simple method for preparation of particles with defined size and reactive surface. The effect of the size and shape of composite components on the homogeneity and stability of mixtures before and after friction process was evaluated.