Study On Surface Modification Of Tunicin Nanowhisker From Halocynthia Roretzi Drasche By Grafting Polymerization

As one of the most abundant and environmentally friendly natural biopolymers in the world, cellulose is widely used because of its excellent mechanical properties, extensive resource and low costs. Natural cellulose is composed of crystalline region and amorphous region, the latter is more sensitive to acid while the former is relatively stable. Therefore, cellulose nanowhiskers can be prepared by acid hydrolysis of cellulosic raw materials. Tunicin nanowhisker(TNW) is a special kind of animal cellulose nanowhisker which can be extracted from the mantle of sea animal of ascidians. TNW is known to have high strength, high modulus, relatively high aspect ratio, low density, biodegradability and biocompatibility, which make it a suitable candidate for composite reinforcement. One of the drawbacks in using TNW is its polar surface due to the hydroxyl groups on the cellulose chain, which limits its application to polar matrix. Surface modification of TNW by grafting copolymerization can dramatically improve its compatibility with low-polar matrix and greatly expand its range of application.In this paper. the mantle of Halocynthia roretzi Drasche was used as raw material for the preparation of TNW. The mantle was disintegrated, degreased and deproteinized. Subsequent hydrolyzation with sulfuric acid gave a stable suspension of TNW (tunicin nanowhisker). The diameter and the length of the TNW were about70nm and2-5μm respectively, and the aspect ratio was about30-70. The cellulose structure for TNW was confirmed by the characteristic absorption in FT-IR spectroscopy.The TNW was surface modified by grafting copolymerization with MMA (methyl methacrylate) using CAN (cerie ammonium nitrate) as initiator under acidic condition. Orthogonal test was planned to study the effects of polymerization condition on the grafting yield. The TNW-g-PMMA (tunicin nanowhisker-graft-polymethyl methacrylate) was obtained with grafting yield at109.8%when the reaction volume was100mL, the amount of TNW was0.25g, the initiator concentration was0.008mol/L. the initiation time was15min. the monomer concentration was0.2mol/L, the nitric acid concentration was0.08mol/L, the reaction temperature was35℃and the reaction time was4h, respectively. The hydrophilicity of the product declined significantly and could be dispersed in MMA. Characterization by FT-IR, SEM and TGA showed that PMMA was successfully grafted to TNW without discernable change in the backbone of TNW, the surface became rough and the thermostability was improved dramatically.Advantages of PMMA render it the most popular denture base polymers, however, there are still some disadvantages such as the low strength and tendency to fracture. TNW-g-PMMA/PMMA composite has been prepared by adding TNW-g-PMMA to liquid for denture acrylic without changing the preparation procedure of denture base polymers. Flexural strength and flexural modulus of the composite were tested by the electronic universal tensile stretm tester, and the influence of added amount of reinforcement on the mechanical property was determined. It was demonstrated that when the mass fraction of TNW-g-PMMA in liquid for denture acrylic was2%. the flexural strength and the flexural modulus of the composite increased15%and11%, respectively. The SEM images illustrated that the fracture surface of specimen became rough as the addition of TNW-g-PMMA increased. The phenomena indicated that more energy was consumed, which was in accordance with the results of mechanical property tests. In summary, the addition of TNW-g-PMMA can efficiently improve the mechanical property of denture base polymers.A small quantity of monomer would remain unpolymerized during the processing of denture base polymers which would be released and cause adverse effects in practice. The international standard clearly stipulates the upper limit of residual monomer in denture base polymers. HPLC (high performance liquid chromatography) was used in this study to determine the amount of residual monomer in TNW-g-PMMA added polymer and the data were compared with those for control group. The results revealed no distinct deviation among each group as the amount of TNW-g-PMMA increased. Moreover.the amount of residual monomer for each group was far below the international standard.