Effect Of Crosslinking Reaction Research Articles

Enhanced positive temperature coefficient effect by crosslinking reaction for silicone rubber/carbon black composites with high pressure sensitivity

AbstractPositive temperature coefficient (PTC) composites are usually made of crystalline plastics and conductive fillers, but they are not suitable for flexible electronic devices because of their high rigidity. Rubber‐based PTC composites are flexible but their PTC intensity is low. In this work, based on the effect of crosslinking reaction on the electrical conductivity of silicone rubber composites, silicone rubber/conductive carbon black composites with an obvious PTC effect were prepared. Compared with the hydrosilylation crosslinking reaction, the peroxide crosslinking reaction has much more obvious decrease in electrical conductivity of the composites. The conductive percolation threshold of the composites was 4.98%. A composite filled with 5.98% conductive carbon black showed obvious PTC effect at circa 150°C, which can be attributed to the re‐aggregation of conductive carbon black in silicone rubber during the crosslinking process. The composite with an obvious PTC effect was well used in an overheating protection device. The composite exhibited an excellent pressure‐sensitivity of conductivity.

Effects of crosslinking reaction and extension strain on the electrical properties of silicone rubber/carbon nanofiller composites

AbstractStretchable conductive silicone rubber (SR) composites are important in wearable electronic devices and the crosslinking of SR composites is necessary for their applications. But the effect of the crosslinking reaction on the electrical conductivity of SR composites is rarely reported. In this article, the effect of crosslinking reaction on the electrical conductivity of SR composites filled with conductive carbon black, carbon nanotubes, and graphene are studied. The crosslink density of SR composites increases with increasing curing time, but the electrical conductivity decreases sharply at the early stage of crosslinking, especially for SR/conductive carbon black composite, which is ascribed to the reaggregation of conductive nanofillers in SR during the crosslinking process. The elastic modulus of the three SR composites gradually increases while the elongation at break decreases with increasing curing time, and the SR/carbon black composite shows ultra‐high elongation at break (1578%). In addition, SR/graphene composite is more sensitive to the extension strain than SR/carbon black and SR/carbon nanotubes composites, and its gauge factor is 414 at the strain ranges of 3–25%. This research work brings a new method to optimize the crosslinking structure of conductive SR composites.

Preparation and characterization of β-cyclodextrin grafted silk fabric

ABSTRACTSilk fabrics were treated by β-cyclodextrin (β-CD) in the presence of citric acid (CA) as crosslinking agent and sodium hypophosphite (SHP) as catalyst using pad dry cure technique. CA is expected to react with β-CD and hydroxyl groups of silk fibroin via esterification reaction. Four independent factors including curing time, curing temperature, β-cyclodextrin, and citric acid concentrations were selected, and effects of these factors on the weight gain of the samples were examined. Fourier transformed infrared spectrometer (FTIR), weight gain, differential scanning calorimetry (DSC), Thermal gravimetric (TGA) and differential thermal analysis (DTA), and field-emission scanning electron microscope (FE-SEM) were employed to confirm the changes of the silk fabrics. The effect of crosslinking reaction on the color changing of samples was investigated by measurement yellowness index of the treated fabrics. The results revealed that the weight gain could reach up to 22% when fabric was treated with 50 g/L β-CD, 100 g/L CA under 170°С for 3 min. FTIR and thermal analysis demonstrated that β-CD had been grafted onto silk fabric successfully.

Adhesion properties of soy protein crosslinked with organic calcium silicate hydrate hybrids

ABSTRACTThe objective of this work was to investigate if inorganic calcium silicate hydrate (CSH) hybrids would improve soy protein wet adhesion properties. 3‐aminopropyltriethoxysilane (APTES) was used as a crosslinking agent to make covalent linkage between organic soy protein and inorganic CSH phases. Soy protein–calcium silicate hydrate (MSP‐CSH) composites with different mole ratio of APTES were prepared and the effect of crosslinking reaction on physicochemical properties such as thermal, rheological, FTIR spectroscopic, and morphological and adhesion properties were studied with physical aging effect. Covalent linkage was observed between CSH and soy protein using the FTIR technique. With aging effect, the denaturation temperature (Td) and enthalpies (ΔHd) of each fraction of soy protein increased in DSC thermograms, representing higher thermal stability, and the viscoelasticity of the composites also increased. The roughly coated surface of the MSP‐CSH composite was observed in SEM images. All these changes further confirmed the interaction between CSH and soy protein molecules. Dry and wet adhesion strength of the MSP‐CSH composites was higher than the control MSP alone. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40693.