Preparation And Characterization Of Hydrophobic Silylation Modified Nanocellulose

Due to the advantages of wide sources,excellent mechanical property,degradability and low coefficient of thermal expansion,nanocellulose(NCC)can be used as the reinforcing agent of hydrophobic polymer matrices.However,the hydrophilic nature of NCC usually limits the consistency between the NCC and the matrix.The hydrophobicity modification is an effecient method to transform the polar hydroxyl groups into nonpolar moieties of NCC which is hence able to enhance interactions with the matrix.NCC with excellent hydrophobic properties can be obtained by different silane modifiers,like long carbon chain chlorosilane,dodecyltrimethoxysilane and Poly(methylhydrogen)siloxane.The main achievements are as follows:Hydrophobic NCC were prepared by dodecyltrichlorosilane and octadecyltrichlorosilane.Then the physical and chemical properities of NCC before and after modification were analyzed systematically.This modification was an efficient and plain operation process.The water contact angle(WCA)indicated the WCA increased as the content of modifier increased.When the content of modifier was 3%,NCC could be modified from hydrophilic to hydrophobic.And when the content of modifier was 20%,the WCA of dodecyltrichlorosilane and octadecyltrichlorosilane modified NCC were 140.8° and 146.6°,respectively.However,the chlorosilane was too active to be stable.To conquer this drawback,dodecyltrimethoxysilane modification with easily controlled process was used.Dodecyltrimethoxysilane was grated onto the surface of NCC by use of γ-(2,3-epoxypropoxy)propytrimethoxysilane(KH560)as coupling agent.There were two steps,firstly KH560 grafted NCC(KH560-NCC)was fabricated by ring-opening reaction of epoxy goup for KH560 and hydroxyl group for NCC;and dodecyltrimethoxysilane(C12-Si)was grafted onto KH560-NCC through hydrolytic polymerization.Single factor experiment was applied to optimize the reaction conditions for KH560 grafted NCC.And then a discussion was developed to research the relationship between pH,modifier content,time and reaction of C12-Si and KH560-NCC.It was found out that the process of NCC modified by C12-Si was tedious and multi-step although this way would overcome the disadvantage from chlorosilane.So we proposed a new hydrophobic modification for NCC surface modification by using Poly(methylhydrogen)siloxane(PMHS)with active Si-H groups,which are very active to hydroxyl groups of NCC,followed by dehydrogenation reaction.The hydrogen contents of PMHS were 0.18%,1.0%and 1.5%.The NCC was thought to react with PMHS at room temperature in the presence of catalyst.The results showed that PMHS with the hydrogen content of 1.5%had best modified effect.With the addition of PMHS was 0.0005%,the WCA of NCC was 135°.