Study On Natural Rubber/Cotton Fiber Composites

Short cotton fiber is a kind of natural product in abundance of cellulose. Cotton fiber reinforced rubber composites have superior physical mechanical properties for its easy processability, lightweight and promising potential applications. In this dissertation the effect of fiber content, orientation and length on the properties of composites, the effect of acetylation on the surface characteristics of fibers, as well as the effect of Bis(3-triethoxysilylpropyl) tetrasulfide (TESPT) and maleated natural rubber, used as coupling agent separately, on the properties of composites were studied.Natural rubber/cotton fiber composites were prepared via mechanical blending. Fiber orientation increased with the increase of fiber content, and it reached the maximum when 30 phr fibers were added, after that the fiber orientation slowly decreased; With the increase of fiber content, the hardness of composites increased, while the tensile strength and elongation at break of composites decreased; Stress-yielding points occurred in the tensile process, and the yield strength, initial modulus and modulus at a definite elongation increased with the increase of fiber content; longitudinal fibers had a better reinforcing ability than the transverse fibers did; with the increase of fiber content the composites required longer time to reach the swelling equilibrium; longer fiber reinforced composites had lower tensile strength, elongation at break and better anti-swelling properties than shorter one reinforced composites did.Heterogeneous cotton fiber surface acetylation with acetic anhydride was performed in an oil bath at 150 0C with Na2CO3 as a catalyst to enhance the reaction activity. The effect of reaction time on fiber acetylation was characterized by the ester content of acetylated fibers, (attenuated total reflectance-fourier transform infrared) ATR-FTIR, (X-ray diffraction) XRD, static and dynamic contact angle measurements and (field emission scanning electron microscopy) FESEM. The ester content increased with increasing reaction time, and the increase of ester content was not distinct at the reaction time over 90 min. The emergence and intensity of the absorption peak characteristic of C=O and the reduction of the absorption peak of O-H clearly proved the occurrence of acetylation. The results of XRD showed the fibers exhibited the typical XRD pattern of cellulose I and the diffracted intensity decreased after acetylation. Static and dynamic contact angle measurements demonstrated the enhanced hydrophobicity and the decreased surface energy along with increasing reaction time. FESEM micrographs showed the acetylation removed the wax layer of fibers and smoothed the fiber surfaces.Bis(3-triethoxysilylpropyl) tetrasulfide (TESPT) was used as in situ surface modifier to improve the interfacial adhesion. The crosslink density, interfacial adhesion, mechanical properties, dynamical mechanical properties and morphology of composites were investigated. The composites with TESPT had higher crosslink density, suggesting the participation of TESPT into the vulcanization network; Lorenz-Park plots showed the interfacial adhesion was enhanced with TESPT; The composites with TESPT showed better mechanical properties, higher initial modulus and yield strength than that of the composites without TESPT; Schematic tensile process was used to explain the mechanical observations; Dynamic mechanical analysis (DMA) proved the composites with TESPT had higher storage modulus, lower damping values than that without TEPST and the coarse surfaces of the pull-out fibers implied the enhancement of interfacial adhesion.Maleated natural rubber (MNR) was prepared by blending natural rubber and maleic anhydride (MA) in an internal mixer at 150 oC through mechanochemistry. The graft reaction of MA onto NR and the possible hydrogen bonding formed between fiber and MA were confirmed by Fourier transformation infrared spectrometer (FTIR). The content of grafted MA increased with increasing MA content in the graft reaction. The composites showed better mechanical properties with MNR that contained higher MA content. The MNR with 20 phr MA was used to improve the interfacial adhesion. The results of Kraus equation showed that the presence of MNR favored the reinforcement of fiber on NR. The fibers pulled out of composites with MNR had coarse surfaces, and the holes left were rough and heavily distorted. The composites with MNR exhibited higher modulus and tensile strength. DMA showed the storage modulus increased with increasing fiber content, the incorporation of MNR further increased the storage modulus of composites at the same fiber content.