Study On Application Of Pretreated Short Cotton Fiber/EPDM Composite

Short fibers reinforced rubber composites (SFRCs) are noted for a combination of properties such as high modulus, excellent dimensional stability, good creep and piercing resistance. However, the poor dispersion of short fibers in the rubber matrix and the weak interfacial adhesion between the short fiber and the rubber phase are the two major factors, limiting the application of SFRC. Especially, the dispersion of the short cotton fiber (SCF) becomes more difficult because of the formation of hydrogen bond and bundles of fibers.In the past, little attention was given to the SFRCs. Until in recent years, these rubber composites attract more and more attentions due to their advantages on the rich source and the less pollution.In this thesis, several dispersants and modifiers were chosen to treat SCF by a simple and unique way. And the blending of EPDM and pretreated SCF were prepared. The effects of pretreated SCF on the structure and properties of the SFRC were also investigated by some modern testing methods such as RPA and SEM. In addition, the overall properties of the pretreated SCF composites are also assessed in comparison with those of the pretreated nylon cellulose DN66 compounds and the short lignin-cellulose fiber compounds.The results are showed as following:1, Adopting the combination of proper dispersants and modifiers for pretreating wasted SCF improves the dispersions of SCF in EPDM and the interfacial adhesion, enhances the reinforcement effect of SCF on EPDM remarkably. Meanwhile the pretreated SCF exerts little apparent effects on the curing properties of the rubber mixes and the heat aging property of the vulcanizates.2, Compared with the equivalent unmodified SCF, the pretreated SCF with the dispersant FP (a kind of compound containing ethers bond and epoxy group) imparts the rubber composites with higher tear strength and tensile strength, as well as with the similar values of the elongation at break, the dispersant FK (a kind of compound containing senior fatty acid) pretreated SCF obviously improves the tensile modulus of the SFRC, while maintaining its tensile strength and tear strength, dispersant FC (a kind of fatty ester sulphonate ) or dispersant FJ (a kind of senior fatty alcohol) pretreated SCF obviously improves tear strength and elongation at break, while decreaseing its tensile strength of SFRC, and dispersant FS (a kind of compound containing hydroxyl group and epoxy group) or dispersant FZ( a low relative molecular mass fatty acid salt) pretreated SCF decreases the mechanical properties of SFRC. In all cases, the contents of dispersant within the range of 2.5 wt% to 5.0wt% are appropriate for achieving a better dispersion effect of the SCF.3, Adopting the same content and within the range of 2.5wt%～5.0wt%, some modifiers, i.e., the modifier ZF ( a kind of silane coupler containing more sulfur bond), the modifier GL (a kind of titanate coupler) or the modifier YQ (a kind of Al-Ti compound coupler) , could improve the adhesion between the SCF and the rubber matrix compared with unmodified SCF. The SFRC containing the modifier ZF shows the highest mechanical properties.4, Compared with the equivalent unmodified SCF, The modified SCFs pretreated with the combination of FK and ZF, or the combination of FP, FC, FJ and YQ respectively, significantly improve the tear strength and the tensile strength of the SFRCs. Furthermore, the pretreated SCF with the combination of FK and ZF obviously decreases the elongation at break of the rubber compound, but improves the tensile modulus. The SFRCs pretreated with the combination of FP, FC, FJ and the modifier YQ show the improved values of elongation at break 2 to 3 times higher than the unmodified SCRC.5, Within the range of 2.5 to 20.0phr, the pretreated SCF with the combination of the dispersant FC and the modifier YQ imparts the rubber composite with the highest tensile strength in relation to the same amount of pretreated nylon cellulose DN66 or the short lignin-cellulose fiber E-140, respectively. In addition, the SFRC containing both FC and YQ shows the higher value of elongation at break than the pretreated nylon cellulose rubber composite, but the comparable value as the short lignin-cellulose fiber E-140.6, The RPA results obtained from the various scanning conditions, that is different temperature, frequency and strain, obviously indicate that the higher elastic modulus values of the rubber mix or the vulcanizate both reinforcing by the pretreated SCF with the combination of 5.0wt% FK and ZF were achieved, compared to those of the corresponding samples with or without unmodified SCF.7, The SEM images of tearing fracture surface of the composites show that the unmodified SCF results in a poor distribution within the rubber matrix and a weak adhesion with the rubber phase. While the modified SFRCs reinforcing with the pretreated SCFs, using the combination of 5.0 wt% dispersant FK and 5.0wt% modifier ZF, 2.5wt% FC and 2.5wt% modifier YQ, 2.5wt% dispersant FJ and 2.5wt% modifier YQ, 2.5wt% dispersant FP and 2.5wt% modifier YQ, respectively, show a more uniform distribution of the fibers within the rubber matrix. Hence the fracture surfaces of the composites appear to be dominated by fibers breakage due to the improved interfacial adhesion between the SCF phase and the rubber phase.