Preparation And Characterization Of Polyurethane Elastomer Composites With Cellulose Nanocrystals Extracted From Office Waste Paper

Polyurethane elastomer has excellent comprehensive properties and is widely used in various fields of the national economy.Thermal stability of polyurethane elastomer,however,is poor,and it is easy to soften and decompose at high temperature,which limits its application in high temperature processing or high temperature service area to some extent.Cellulose nanocrystal has perfect crystal structure,good thermal stability and excellent mechanical properties which is considered to be the ideal filler for polymer materials.Besides,as a kind of environmental-friendly biomacromolecular material,cellulose nanocrystal is also renewable and degradable with low cost.This paper launched the subject of preparation and characterization of thermostable polyurethane elastomer composites in order to improve heat resistance of polyurethane by adding cellulose nanocrystal and widen the applicable range of polyurethane elastomer.This paper prepared polyurethane elastomer with a certain crystallinity and morphology by adjusting raw materials with the stepwise polymerization method,for the purpose of providing heat resistant polyurethane matrix for cellulose nanocrystal/polyurethane elastomer composites.The results showed that chain extender and isocyanate affected microphase separation,low temperature properties and heat resistance of polyurethane elastomer greatly.Polyurethane elastomer prepared with para-phenylene and 1,4-butanediol(PPUE1)had better low-temperature toughness,higher stiffness and heat resistance,and was the best matrix to prepare heat resistant composites.Preparation technique of cellulose nanocrystal from office waste paper with a low cost was proposed so an effective method to recycle waste paper was constructed.Deinked office waste paper pulp(DP)was prepared and then extraction of cellulose nanocrystal from DP was carried out by sulfuric acid hydrolysis.The optimum preparation parameters were confirmed by analyzing structure and properties of cellulose nanocrystal.Cellulose nanocrystal with the yield of 61.5%,purity of 95.17%and crystallinity of 71.4%was prepared by using sulfuric acid hydrolysis of 59%under 45℃ for 1 h and was marked as PCNC.A new idea to prepare thermostable polyurethane elastomer composites by adding PCNC was presented.A series of polyurethane elastomer composites based on PPUE1 matrix and PCNC fillers(PCNC/PUE)were prepared by the combined in situ polymerization method and prepolymerization method.The influence of the additive content of PCNC on properties of polyurethane elastomer,especially heat resistance,was studied and the interaction mechanism between PCNC and polyurethane matrix was revealed.The results showed that PCNC could induce soft segments and hard segments to arrange orderly by the cooperation of hydrogen bonds and covalent bonds between PCNC and polyurethane,resulting in the reinforced soft and hard segments and the improved properties of polyurethane,especially heat resistance.The additive PCNC made the initial thermal decomposition temperature of polyurethane increase by 21℃.The interactions between PCNC and polyurethane became stronger with the increasing additive content of PCNC.When the additive content of PCNC was of 2 wt%,the interaction between PCNC and polyurethane became the strongest and composites with PCNC of 2 wt%(PCNC/PUE2)had the best performances including the highest stiffness,best thermo-mechanical properties and heat resistance,and the worst water absorption.The differences between PCNC and other cellulose nanocrystals were studied and the structures and properties of polyurethane elastomer composites reinforced with PCNC and other cellulose nanocrystals were also studied.The results showed that the interactions between other cellulose nanocrystals and polyurethane like those between PCNC and polyurethane,which were built by hydrogen bonds and covalent bonds.Polyurethane elastomer reinforced with PCNC had the highest stiffness and best heat resistance compared with polyurethane elastomer reinforced with other cellulose nanocrystals,which might be associated with the stronger interactions between PCNC and polyurethane,higher crystallinity and better heat resistance of PCNC.The influence of the dimensions of waste paper fibers on properties of polyurethane elastomer was studied.Firstly,deinked pulp/polyurethane elastomer(DP/PUE)was prepared by the combined in situ addition method and prepolymer method.Then,the comparison of PCNC/PUE and DP/PUE was carried out.The results showed that the interactions between DP and polyurethane were weaker than those between PCNC and polyurethane.PCNC was more efficient to improve stiffness and heat resistance of polyurethane.This paper extracted cellulose nanocrystal from office waste paper,and then prepared polyurethane elastomer composites with excellent performances,which not only provided a new approach to recycle office waste paper but also prepared low-cost polyurethane composites with high heat resistance,extending the application range of polyurethane.It had both economic and environmental benefits and conformed to the sustainable developmental strategy.