Surface Modification Of Cellulose Nanocrystals And Its Reinforcing Function In Composite Meterials

As a kind of natural polymer,nanocellulose has the property of high crystallite,high young modulus and mechanical strength,as well as the good biocompatibility,biodegradability,non-toxicity,and availability from renewable resources,nanocellulose as a green reinforcement has attracted great attention,showing a great application prospects in preparation of high performance nanocomposite materials.Nanocellulose has the property of forming strong hydrogen bonding due to their surface hydroxyl,and easy chemical modification.Nanocellulose fibers(NCFs)and cellulose nanocrystals(CNCs)were prepared by physical and chemical methods,respectively.NCFs were used to prepare nanocellulose aerogels.CNCs were used as nanofillers to improve properties of two-component waterborne polyurethanes(2K-WPU)and room-temperature vulcanization silicone rubber(RTV),respectively.NCFs reacted with 1,4-butanediol diglycidyl ether to prepare nanocellulose aerogels,which was catalyzed by SnCl4.aerogels with continuous network pore structure still maintain their cellulose I crystalline structure,aerogels started to degrade above 250?.When the amount of 1,4-butanediol diglycidyl ether is 2 times as much as NCFs,the density of aerogels is 0.0202 mg/cm3,and aerogels can absorb water 36 times their own weight.90% recovery degree was recovered when the aerogels was immersed in water and DMSO.Aerogels were reused 5 times,water absorption ability still up to 30 times.CNCs were used as nanofillers to improve properties of 2K-WPU.The morphology,structure,thermal,and mechanical properties of the 2K-WPU/CNCs nanocomposites were investigated.It demonstrated that CNCs were compatible with 2K-WPU and dispersed homogeneously in the polymer matrix.CNCs as nanofillers improved tensile strength of 2K-WPU significantly.Tensile strength of 2K-WPU/CNCs composite films increased from 2.63 MPa to 10.22 MPa with increasing CNCs amount from 0 to 9wt%,and the increase was about 288.6%,their elongation was decreased from 644.3% to 87.2%.With the addition of more CNCs,the thermal stability and the glass transition temperature of 2K-WPU nanocomposites were also improved.We used urethanization technique for surface modification of CNCs.3-isocyanatopropyltrimethoxysilane(IPMS)was used for improving dispersibility of the CNCs in matrix for RTV matrix.The silylated CNC(SCNCs)were prepared and incorporated into commercial silicone rubber via vulcanization processes.SCNCs had strong reinforcing effect on the RTV matrix,compared to neat RTV,with only 3wt% SCNCs incorporated,the tensile strength increased from 0.46 MPa to 1.45 MPa,and the increase was about 215.2%,the elongations were decreased from 493.4% to 444.0%,and the decrease was about 9.9%.With the addition of more SCNCs,the thermal stability of RTV nanocomposites was also improved.