Preparation and Mechanical Properties of Micro- and Nano-sized SiC/Fluoroelastomer Composites

Microand nano-sized SiC/fluoroelastomer （FKM） composites were prepared by a mechanical mixing method. These composites were first characterized by a rotorless rheometer. Then the effects of micro- and nano-sized SiC on hardness, static and dynamic mechanical properties of the composites were investigated. The increasing amount of the SiC filler increased the curing efficiency of the biphenyl curing system, which was evident from the rheometric properties of the resulting composites. The tensile properties of composite increased with the increasing of micro- and nano-sized SiC content. When the micro- and nano-sized SiC content was higher than 20 phr, the composites showed almost unchanged tensile properties. The increasing of the tensile property was mainly attributed to the well dispersed micro- and nano-sized SiC particles characterized by SEM images. Compared to pure FKM, the composites exhibited a higher glass transition temperature and lower tan peak value.

STUDIES ON SELF-VULCANIZING FLUOROELASTOMER/PHENOL HYDROXY SILICONE RUBBER BLENDS

Self-vulcanizing blends of phenol hydroxy silicone rubber (PHSR) and fluoroelastomer (FPM) were prepared. Vulcanized rubbers with lower glass transition temperature (T(g)) were successfully obtained. The results of dynamic mechanical analysis (DMA) show that the vulcanized FPM/PHSR (10 phr) blend has only one T(g) temperature, demonstrating the well compatibility between FPM and PHSR. The thermogravimetric analysis (TGA) demonstrates that the PHSR do little damage to the thermal stability of FPM. The vulcanization characteristics of the FPM/PHSR blends were analyzed by using oscillating disc rheometer (ODR). The results show that FPM/PHSR blends have smaller S(min) values and longer scorch time than that of FPM with the same level of bisphenol AF curing agent. It means that FPM/PHSR blends have better processability and curing security. Better mechanical properties can be gained for FPM/PHSR blends at appropriate level of PHSR.

Microstrueture and Properties of Fluoroelastomer/Butadiene-Acrylonitrile Rubber Interpenetrating Polymer Networks

Interpenetrating polymer networks （IPNs） based on fluoroelastomer/butadiene-acrylonitrile rubber （FKM/NBR） by molten blending at a high temperature and chemical cross-linking of two components were prepared. The influence of the two networks component on the mechanical properties and thermostabilities was studied. The experimental results show that the mechanical properties of the IPNs are superior to those of the individual FKM and NBR networks due to forming the case of interpenetrating and intercross-linking between the two networks, the mechanical properties and thermal resistance exhibit higher values when 80/20 （w/w） FKM and NBR is blended and respectively cured simultaneously. The co-continuous morphology of the IPNs in the blends of 80/20 （w/w） FKM/NBR is found by transmission electron microscopy （TEM）, the differential scanning calorimetry （DSC） determination shows that the blends of 80/20 （w/w） FKM/NBR have better compatibility, and the glass transition temperature of the elastomer is -21.5 ℃.

Study of intumescent flame-resistant fluoroelastomer

The efficiency of different intumescent flame-retardant （IFR） formulations designed to improve the flame resistance of fluoroelastomer （ FKM ） composites was studied. The proportion of ammonium polyphosphate （APP） with charring-foaming agent （CFA） in IFR systems, and the addi- tion of synergists zinc borate （ZB） and ketonealdehyde resin （ KR120 ） were investigated to show their effect on flame resistance of FKM. According to flame resistance tests, when the mass ratio of APP to CFA was 4：1 as well as the loadings of IFR, ZB, KR120 were 83 parts per hundred resin （phr）, 13phr, 25phr, respectively, the FKM-KR120/IFR-ZB composites had good synergetic flame resistant effect. TGA data showed that IFR and synergists could obviously lower the maximum weight loss rate of FKM composites and effectively increase the char residue at high temperature. The morphological structures of the composites observed by scanning electron microscopy （SEM） demonstrated that the addition of ZB and KR120 could clearly reduce the cracks in char residue and make the char layer structure more integrated and compact.

Accelerated Aging Behaviors and Mechanism of Fluoroelastomer in Lubricating Oil Medium

The aging behaviors and mechanism of fluoroelastomer(FKM)under lubricating oil(FKM-O)and air(FKM-A,as a comparison)at elevated temperatures were studied from both physical and chemical viewpoints.The obvious changes of mechanical and swelling performances indicate that the coupling effect of lubricating oil and temperature causes more serious deterioration of FKM-O compared to that of FKM-A.Meanwhile,much stronger temperature dependence of both bulk properties and micro-structures for FKM-O is found.Three-stage physical diffusion process is defined in FKM-O due to the competition between oil diffusion and elastic retraction of network.FTIR results reveal that the dehydrofluorination reaction causes the fracture of C-F bonds and produces a large number of C=C bonds in the backbone.The coupling effect of oil medium and high temperature could accelerate the scission of C=C bonds and generate a series of fragments with different molecular sizes.The TGA results,crosslinking density Ve,and glass transition temperature Tg derived from different measurements coherently demonstrate the network destruction in the initial stage and the simultaneous reconstruction occurring at the final stage.The newly formed local network induced by reconstruction cannot compensate the break of the original rubber network and thus only provides lower tensile strength and thermal stability.

Design and Properties of Fluoroelastomer Composites via Incorporation of MWCNTs with Varied Modification

Multi-walled carbon nanotubes(MWCNTs)modified with silane coupling agent A-1120(MWCNTs-A1120)were prepared.Compared with the raw MWCNTs,acidified MWCNTs(MWCNTs-COOH),and MWCNTs grafted with EDA(MWCNTs-NH2),MWCNTs-A1120 have the best dispersion in fluoroelastomer at the same doping ratio.Therefore,fluoroelastomer/MWCNTs-A1120 composite has the best mechanical properties with tensile strength of 13.92 MPa and elongation at break of 111.78%.Then,the effects of doping amount of MWCNTs-A1120 on the electrical properties of the composites were investigated.The dielectric constant of the composite increases with the increase of MWCNTs-A1120,and the dielectric loss does not change much at the low doping amount such as 0.5 wt%.When the doping amount of MWCNTs-A1120 is 5 wt%,the dielectric constant and the dielectric loss value are greatly increased,and the volume resistivity is greatly decreased,which proves that the conductive network is formed in the composite,so the filling amount of 5 wt%is the percolation threshold.The tensile deformation of the sample also affects the electrical properties of the composites.As the tensile deformation increases,the dielectric constant and dielectric loss of the composite decrease.For the composite with 5 wt%MWCNTs-A1120,excessive tensile deformation will destroy the conductive network structure of the composite,so the composite will change from conductive material to dielectric material.Therefore,such composite is a good candidate for flexible conductive material or flexible dielectric material used in harsh environments such as high temperatures and various aggressive solvents.