Study On Ionomer, Cellulose Nanofibers Reinforced Wood Plastic Composites

Recently,wood plastic composites(WPC) draw more and more attention because ofabundant raw materials and excellent properties. However, WPC products still have a lot ofdisadvantages on the market, such as large specific weight, low strength, especially poor impacttoughness, and the main reason is that wood floor only plays a role in filling phase, other than theeffect of reinforcement phase. Therefore, more and more scholars focus on study ofreinforcement modification of WPC. Two reinforcing materials were used to modify WPC in thispaper, one is ionomer, and the other one is biocellulose nanofibers.In this paper, in order to evaluate the effect of improving the compatibility and impacttoughness, WPC was extruded by HAKKE minilab using HDPE as matrix, and wood floor asfiller, and compared with the effect of traditional coupling agent-maleic anhydride graftedpolyethylene(MAPE), the conclusions were as follows:(1)The influence of ionomer on the rheological properties: both of the shear stress andapparent viscosity showed decline trend with sodium ionomer increasing, which indicated thesodium ionomer could improve the flow ability of WPC melt. Compared with MAPE, the shearstress and apparent viscosity of WPC adding4%sodium ionomer and4%zinc ionomer weremuch lower, which also revealed ionomer could improve the flow ability of WPC much moreefficiently.(2)The effect of ionomer on mechanical performance of WPC: the tensile strength and thebenging strength of WPC showed ascending trend with ionomer increasing, but the bendingmodulus showed decline trend, and the bending strength of WPC adding sodium ionomer washigher than that adding MAPE, which demonstrated ionomer played a part in coupling agent, andimprove the interfacial strength.Ionomer played an important role in improving the impact toughness of WPC, and theimpact toughness of WPC was40.2J/m when adding4%sodium ionomer. The impact toughnessshowed approximate linear enhancement with ionomer increasing.(3) The effect of ionomer on the coefficient of thermal expanding of WPC: in the lowtemperature range（-20℃-30℃）, the LCTE of WPC adding4%sodium ionomer was64.11×10-6/℃, which was reduced61.89%than pure HDPE, both in the low temperature range（-20℃-30℃））and middle temperature range（0℃-60℃）, the LCTE of WPC showed firstlydecreases and then inceases trend with sodium ionomer increasing.(4) The DMA analysis indicated:The storage modulus of WPC adding2%sodium ionomerand4%sodium ionomer were higher than which adding0%sodium ionomer and6%ionomerwhen below60℃, but E’ showed dicline trend as sodium ionomer increased when above60℃. Itis different for loss modulus which showed decline trend at all temperature range. Comparedwith MAPE, the values of E’ for three WPCs was as follows before glass transition point(Tg):4%MAPE>4%sodium ionomer>0%aditives，but over Tg, the E’ of WPC adding sodium ionomer was a little lower than which adding MAPE and0%aditives. The loss modulus of WPCadding0%aditives was much higher than it adding4%MAPE and4%sodium ionomer.(5) The FTIR analysis showed that: it could be found that the carboxyl group was brought inWPC adding4%sodium ionomer, which indicated ionomer and fiber involved chemical reactionand improved the interfacial compatibility of wood floor and polymer matrix.Then the cellulose nanofibers(CNF) were prepared via acid and alkali treatment combinedwith mechanical treatment with poplar floor and cotton as raw material. The CNF was dispersedinto HDPE matrix by vacuum filtration and then all the materials were extruded by a HAKKEminilab, and the effect of WPC reinforced by CNF was as follows:（1）The apparent viscosity of WPC melt showed increased trend with poplar CNFincreasing, which indicated the viscosity of melt was increased by poplar CNF.（2）The MOR and MOE of WPC adding poplar and cotton CNF showed visble increasedtrend as CNF levels increased, and the MOR of WPC without CNF was28.6Mpa，but the MORof WPC adding20%poplar CNF and20%cotton CNF were41.2Mpa and37.1Mpa separately.（3）The LCTE of WPC adding poplar CNF and cotton CNF were both showed declinetrend with CNF content increasing, the only diffrence was the LCTE of WPC adding cotton CNFwas litter higher than which adding poplar CNF.（4）The DMA analysis showed the storage modulus and loss modulus were both increasingas CNF increased, which indicated the adding of CNF enhanced the stiffness and viscosity ofWPC.（5）The SEM photographes showed there was well dispersed net-like fibers on the fracturesection of WPC adding10%and20%poplar CNF using vacuum filtration, and part of silk wasnanoscale. Compared with WPC adding poplar CNF, which adding cotton CNF also had silk onthe fracture section, but the fibers were not clear very much and the dispertion effect was notvery perfect.Finally the CNF/HDPE composite was extruded with poplar CNF as reinfored material, andtwo dispersing mathod was used to make CNF dispersed into HDPE uniformly, one is to usePEO as dispersing agent, and the other is vacuum filtration, and the conclusions were as follows:(1) rheological properties showed that: the shear stress and apparent viscosity both showedapproximatly linear increasing trend with CNF increasing, and the stress and apparent viscosityof WPC using dispersing agent method was much lower than which using vacuum filtrationmethod when the content of CNF was below50%.(2) The MOR and MOE of WPC using two dispersing methods both showed increasingtrend as CNF increased, but which using vacuum filtrition method were little lower than usingdispersing agent method.(3)The LCTE showed adding a little CNF could decreased the LCTE of HDPE, but thelower rate was not evident any more as CNF increasing. The LCTE of composite usingdispersing agent method declined much more than which using vacuum filtrition method.(4) The DMA analysis showed the storage modulus and loss modulus both showedincreasing trend using two dispersing methods as CNF increasd. The maximum storage modulus was7793Mpa using dispersing agent method when CNF content was50%, but the maximumstorage modulus was7582Mpa using vacuum filtration method, but the loss modulus usingvacuum filtration was much higher than using dispersing agent method, which indicated thecomposite prepared using vacuum filtrition method would consume much energy and damperwas much higher, and the dispersing agent method was much better.(5) The SEM photographs showed there exsited well-dispersed silks on the fracture sectionof CNF/HDPE compostes prepared with two dispersing methods, and part of silks werenanoscale, which indicated CNF were well dispersed into HDPE matrix using two methods, butthe silks on the fracture section of composite using dispersing agent method was mcuh uniformand dense, and the part of naked HDPE was lesser.