Study On The Preparation And Properties Of Polyurethane Modified By Cellulose Nanocrystals

Nowadays the interest of many researchers is stimulated to polyurethane because of its outstanding properties,such as high elasticity,high strength,high oil resistance,low wear and other characteristics.Meanwhile,it has made important achievements in the research of chemical structure design,physical modification and chemical modification.However,the traditional filler-modified polyurethane was mostly limited to the organic modification of inorganic materials or the direct addition of organic fillers,without considering whether organic fillers can play a good role in all kinds of polyurethane materials.In this paper,taking cellulose whiskers(CNC)as an example,the polar compatibility of organic fillers on the performance of different types of polyurethane materials was researched.Cellulose whiskers were used to prepare different types of nanocomposites by adding polyether polyurethane or polyester polyurethane respectively by solvent method or in-situ method.A series of characterization methods,including FTIR,XRD,TG,POM and SEM,were used to find out that in solvent method and in situ method results were consistent.The result showed that cellulose whiskers in polyester polyurethane could achieve a better dispersion state when it in the polyether polyurethane got a larger agglomeration.As the FTIR showed,the addition of cellulose whiskers in the polyester polyurethane,the degree of hydrogen bonding was significantly improved,indicating that the existence of the external hydroxyl of the cellulose whiskers was conducive to its dispersion in the polyester polyurethane.By changing the isocyanate diphenylmethane diisocyanate(MDI)into toluene diisocyanate(TDI),the difference was more obvious.Simultaneously,through experimental investigation and the contrast with SEM,it was found that POM was a good way to observe whiskers reinforced the dispersion of polyurethane.M-tolylisocyanate(MPI)modified cellulose whiskers.A series of characterizations proved that the m-tolylisocyanate-modified cellulose whiskers(MPI-CNC)was prepared successfully without prejudicing its original morphology,however,it got the low polarity,high dispersed and high degree of crystallinity.MPI-CNC had good dispersibility in acetone,chloroform and ethyl acetate.Repeating the above experiment resulted in the opposite of the above,which MPI-CNC was well dispersed in polyether polyurethane and a large amount of agglomeration in polyester polyurethane.At the same time,MPI-CNC/PU prepared by in-situmethod was found to be more easily agglomerated in polyester polyurethane than MPI-CNC/ PU which was prepared by solvent method.This showed that the low-polarity MPI-CNC tended to interact with polyether segments due to the similar polarity but to easily repel each other in higher-polarity polyester segments.A series of CNC grafting PU materials were prepared by modified CNC with TDI-80.According to the observation of POM,it could be seen that CNC can obtain good dispersion during the grafting to the polyurethane.And the static mechanical properties showed that the grafting of CNC slightly increased the elongation at break of the material,at the same time,the mechanical properties curve of the original polyurethane material changed.When the content was increased to 5 wt%,the stress-strain curve shows a nearly linear relationship.