Surface Modification Of Microcrystalline Cellulose And Its Effect On Properties Of NRL Composites

Microcrystalline cellulose(MCC)has a relatively complete crystalline structure and high aspect ratio,making it have excellent mechanical properties.Therefore,it can be used as green reinforcing filler of the rubber composites.However,due to a large number of hydroxyl groups on the surface of microcrystalline cellulose,it shows strong polarity.Therefore,the interface interaction between the polar microcrystalline cellulose and non-polar natural latex matrix is very weak,which affects its reinforcement effect on rubber composites.In this study,the polydopamine layer coating modification and the ionic liquid pretreatment method were first used to reduce the particle-particle aggregation between the microcrystalline cellulose.Subsequently,the polydopamine layer coating(PDA)modified MCC(MCC/PDA)and ionic liquid(IL)pretreated MCC(MCC/IL)were used as fillers,and the natural rubber latex(NRL)was used as substrates to prepare natural rubber latex/microcrystalline cellulose(NRL/MCC)composites.These composites had excellent properties.The interactions between the microcrystalline cellulose and polydopamine and the ionic liquid were studied by means of ATR-FTIR,XPS,TGA,XRD,and other characterization methods.The polydopamine layer as a modifier to improve the dispersion of microcrystalline cellulose in the natural rubber latex matrix and on the rubber-filler interfacial interaction of microcrystalline cellulose(MCC)-filled NRL composites were systematically studied by means of micro morphological characteristics,Payne effect,crosslinking density,cure and mechanical properties,and swelling index.The effects of ionic liquids as multifunctional additives on the properties of microcrystalline cellulose reinforced natural latex composites were investigated using the activation energy,curing characteristics,crosslinking density,mechanical properties,scanning electron microscope and dynamic mechanical properties of NRL/MCC/IL composites.The results are as follows:(1)ATR-FTIR,XPS,and TGA showed that the biomimetic adherent PDA layer was successfully coated onto the MCC surface via dopamine self-polymerization through a simple dip-coating method.And there was a strong electrostatic interaction between the ionic liquids and microcrystalline cellulose.XRD analysis showed that the method of polydopamine coating modification and ionic liquid pretreatment did not destroy the crystal structure of microcrystalline cellulose,and the whole reaction was only carried out on the surface of MCC.(2)The surface modification of microcrystalline cellulose by PDA was introduced into the preparation of natural rubber latex/microcrystalline cellulose composites.As expected,compared to the either NRL/MCC system,the results showed that the presence of polydopamine layer would effectively reduce the networking degree of MCC filler,weaken the Payne effect of NRL/MCC/PDA composites,improve the dispersion of MCC in the NRL matrix,thereby moderate enhance the mechanical properties of composite.Additionally,by comparing the curing characteristics,it was found that the M_L and the M_H-M_L difference value of the NRL/MCC/PDA compounds were decreased and increased,respectively.Therefore,these results indicated that the filler-filler interactions of MCC-filled NRL composites were weakened,and the interaction between the rubber-filler interfacial interaction was increased,so that the degree of the composites crosslinking increased.Simultaneously,according to the analysis results of the Q_f/Q_r value of the composite,in the presence of the PDA layer as a modifier,the effective interaction between the non-polar NRL matrix and the polar MCC filler was improved,so that the Q_f/Q_r value of NRL/MCC/MCC composite was slightly lower than that of NRL/MCC system.(3)The ionic liquid was as a multifunctional additive introduced into the preparation process of the natural rubber latex/microcrystalline cellulose composites.Compared with the NRL/MCC system,the results showed that the scorch time(t₁₀)and the positive vulcanization time(t₉₀)of the natural rubber latex/microcrystalline cellulose/ionic liquid(NRL/MCC/IL)composites were exhibited constantly decreased trends as the increasing of IL.Meanwhile,the value of the vulcanization rate constant k was gradually increased.The activation energy was decreased,and the crosslinking density first increased and then decreased a little.Moreover,the results of mechanical properties analysis showed that the mechanical properties of NRL/MCC/IL composites were obviously improved,compared with NRL/MCC system.SEM images exhibited that the contact surface between the microcrystalline cellulose and rubber matrix in NRL/MCC/IL composites were become blurred,the MCC dispersed uniformly and lots of them embedded in the NRL matrix.The Ayala parameter was used to quantitatively calculate the MCC/NRL matrix interface interaction.The results showed that the I value of NRL/MCC/IL composites with an appropriate amount of ionic liquid was larger than that of natural latex composites filled with original microcrystalline cellulose.It indicated that the interfacial strength between the microcrystalline cellulose after ionic liquid pretreatment and natural latex matrix was enhanced.