Study On Efficient Separation And Modification Of Tropical Rubber Wood Cellulose And Its Applications In Biodegradable Films

Rubber wood cutoff is a type of common biomass waste in tropical rubber plantation and rubber wood processing industry,but it has not been deeply exploited and utilized for a long time.It is bound to cause severe environmental pollution and dissipation of biomass resources,if applying improper treatments,e.g.,incineration.To realize the higher-value application of waste rubber wood resource,in this thesis,rubber wood cellulose has been efficiently isolated,purified,and modified for preparation of rubber wood nanofiber products,which have been applied as reinforcing fillers for fabrication of polyvinyl alcohol（PVA）based and polylactic acid（PLA）based composite films.Rubber wood cellulose with purity of 91.3%has been prepared from waste rubber wood（RW）after a series of isolation and purification steps,such as mechanical disintegration,degreasing,delignification and acid treatment.The fibrils of purified cellulose are featured as 10-30μm in diameter and several hundred microns in length.Later,rubber wood cellulose nanocrystal product-1（RW-CNC-1）（diameter:5.7±2.0 nm&length:50-250 nm）has been prepared from rubber wood cellulose by means of a TEMPO/Na Cl O₂/Na Cl O system together with the subsequent sonication.On the basis of 64%sulfuric acid hydrolysis and sonication,rubber wood cellulose nanocrystal product-2（RW-CNC-2）（diameter:7.4±2.7nm&length:less than 400 nm）was prepared.As manifested from the results,both RW-CNC-1 and RW-CNC-2 could reach better dispersion in aqueous phase owing to their respective zeta potential,e.g.,-47.4 m V for RW-CNC-1 and-51.8 m V for RW-CNC-2.In addition,the thermal stability of RW-CNC-1 and RW-CNC-2 declined in different extents due to the introduction of carboxyl and sulfate groups.Taken RW-CNC-1 as a reinforcement agent,RW-CNC-1/PVA composite films were fabricated by blending and thermal treatment was attempted for improvement of water resistance and mechanical properties of the films.It was found that with the increasing dosage of RW-CNC-1,the tensile strength and elastic modulus of composite films increased first and then decreased.When the addition of RW-CNC-1 reached 5%,the tensile strength and elastic modulus reached the maximum values,which were 83.0 MPa and 4.4 GPa,respectively.In addition,the elongation at break of the composite films suffered a significant reduction when more RW-CNC-1 involved.The tensile strength of the composite films can be evidently enhanced by thermal treatment,but the elongation at break on the other hand decreases extensively.Only did the pure PVA film receive improved Young’s modulus after thermal treatment,all the other PVA based composite films did not exhibit obvious difference in terms of elastic modulus before and after thermal treatment.The addition amount of RW-CNC-1 has little effect on the water absorption of the composite films,but this index could be largely reduced by thermal treatment.In order to improve the compatibility between filler and PLA matrix,acetylated rubber wood cellulose（AC-RWC）and acetylated RW-CNC-2 were used to fabricate PLA based composite films.The results show that the mechanical properties of the composite films can be improved by both reinforcing fillers.Compared with the tensile strength of pure PLA film（35.7 MPa）,these values for Ac-RWC/PLA and Ac-RW-CNC-2/PLA are 48.6 MPa and 55.0MPa,respectively,when filler dosage was controlled as 5%.Young’s modulus also increased from 2.6 GPa（pure PLA film）to 3.0 GPa（Ac-RWC/PLA）and 3.9 GPa（Ac-RW-CNC/PLA）,respectively.In addition,Ac-RWC and Ac-RW-CNC can be used as crystallization nucleating agents to improve the crystallization ability of the composite films.