Preparation And Properties Of Modified Cnc/pa6 Composites

PA6,as a multi-purpose semi-crystalline engineering plastic,is widely used in automotive,electronic and electrical,engineering components,sports equipment,textile and other fields.However,with the continuous development of society,there are forward higher requirements of the dimensional stability and the mechanical properties of nylon materials.The development of modified nylon materials has be paid more attention.Commonly used physical modification methods include the addition of nucleating agents to affect their crystallization behavior and the addition of reinforcing fillers to improve PA6's performance.Cellulose nanocrystals(CNC)have an organic nanocrystal structure,high strength,wide source of raw materials and renewable,so it have gradually become a new type of nanofiller for modifying polymer materials.However,similar to other nanomaterials,the nanoscale effect will lead to the problems of easy agglomeration and poor interaction force between the two-phase interface when CNC is added as a filler to the polymer matrix material.In order to obtain high-performance PA6 materials,this paper aims at the chemical structure of PA6 and introduces specific functional groups on PA6 and CNC respectively,which improves the dispersion of CNC and its interaction with PA6.The main research work is carried out in two parts:(1)Preparation of PA6-CH2OH/IPDI-CNC modified materials.First,IPDI surface-modified CNC(IPDI-CNC)was synthesized as a nucleating agent for PA6.At the same time,an appropriate amount of hydroxyl groups were introduced into the PA6 molecular chain.The design used the chemical bond between CNC and PA6 to improve the compatibility and interface force between CNC and PA6.So as to give full play to the nucleation effect of CNC and realize the effective regulation of the crystallization behavior of PA6.The details are as follows:Hydroxymethyl PA6(PA6-CH2OH)was prepared by grafting hydroxymethyl on the PA6 molecular chain through formaldehyde activation of-CONH-in the PA6 molecular chain under acid environment.The effects of phosphoric acid,formaldehyde content and reaction time on the grafting rate were studied.And the effect of grafting rate on PA6-CH2OH water absorption and mechanical properties was analyzed.The best formula and process for preparing PA6-CH2OH was determined as the matrix of modified nylon.At the same time,using-NCO,which was more active in isophorone diisocyanate(IPDI),reacted with-OH on the surface of CNC prepared by acid-decomposed cotton fiber,and introduced isocyanate groups on the surface of IPDI.TG,TEM,elemental analysis,XRD and other methods were used to characterize the product structure.Then,using the solution blending method,IPDI-CNC was added to PA6-CH2OH to obtain a modified PA6 nanocomposite.Through SEM observation,it was found that IPDI-CNC could be evenly dispersed in PA6-CH2OH and form a good interface.Studies on the crystallization behavior,water absorption rate and mechanical properties of PA6 showed that IPDI-CNC could be used as a nucleating agent to effectively increase the crystallinity of PA6,accelerate the crystallization speed,change the nucleation and growth mechanism of PA6 crystals,reduce its water absorption rate,and increase tensile strength,but reduce elongation at break.(2)Preparation of PA6-LA/LA-CNC modified nylon material.The long carbon chain was introduced into the CNC surface through the transesterification reaction,and the long carbon chain side chain was introduced into the PA6 molecular chain,so that CNC and PA6 could form an an organic "buffer layer" between CNC and PA6 through the physical entanglement of the similar long chain structure.It could make the modified nylon material have the performance of strengthening and toughening at the same time.The details are as follows:First,the modified cellulose nanocrystals grafted with lauric acid(LA)on the surface were prepared by transesterification of LA and-OH on the surface of CNC under the activation of N'N-carbonyldiimidazole(CDI).At the same time,LA modified PA6(PA6-LA)was prepared by the high temperature esterification reaction of PA6-CH2OH and LA.Finally,the PA6-LA/LA-CNC nanocomposite was prepared by melt blending.The results of the study on its mechanical properties showed that the preparation of PA6-LA/LA-CNC nanocomposites after modification of CNC and PA6 by LA could significantly improve the elongation at break,and at the same time could increase their tensile strength.strength.