Preparation And Properties Of Wood Plastic Composites By Corn Stalk

As a large agricultural country,China produces a large amount of corn stalks every year.However,the incineration treatment brings great harm to the atmospheric environment,which does not meet the development trend of ecological agriculture in China.It is also not conducive to the realization of the new goal of“Wild China”.The purpose of this study is to solve the problem of recycling of corn stalks.First,the corn stalk was shattered by mechanical method,and the standards sifters were used to sieve the corn stalks fibers(CSF)with 80-100 mesh.In order to enhance mechanical properites of the wood plastic composites(WPC),sisal fiber(SF)was introduced as reinforcer.The PVC composites reinforced by CSF and SF were fabricated by a hot-press molding method.The contradiction between CSF in hydrophobic and non-polar polymers leads to inapposite system due to the lack of moderate compatibility and adhesion between the fiber and matrix.The complex coupling agent and the chemical crosslinking technique was supposed to increase the compatibility between the CSFs and polypropylene(PP)matrix.The research work of this thesis has very important significance for the utilization of CSFs in WPC.There are three parts in our work:(1)The CSF was used as filler instead of wood flour(WF)to prepare polyvinyl chloride(PVC)based WPC.High performance SF was introduced to improve the properties of CSF/SF/PVC composites.The effect of SF length and loading on the mechanical and the water absorption behaviours of WPC were investigated in detail.The results indicated that the application of CSF made a similar improvement in tensile strength compared to WFPC.The introduction of 5 mm in length and 5 Phr at content(CSFSFPC-5)resulted in increasing the mechanical properties and decreasing the moisture absorption property.Compared with CSFPC and WFPC,the flexural strength of CSFSFPC-5 was increased by 56.7%and 50.3%,the flexural modulus of CSFSFPC-5 was increased by 47.4%and 52.9%,respectively.SEM was carried out to observe the fracture surfaces of the samples and the distribution of CSF and SF in PVC were analyzed.Finally,the hybrid enhancement mechanism of SF in PVC matrix was discussed.(2)Maleic anhydride compatibilizer(MAPP)and chitosan(CS)are mixed and used as a complex coupling agent to modify the PP matrix.And 5wt%NaOH and 10wt%NaOH aqueous solution were used to treat CSF,respectively.The effect of complex coupling agent and alkali treatment on the mechanical properties of the CSF polypropylene matrix composites was investigated.Morphological observations of the fracture surfaces were accepted to confirm CSF dispersion and wetting with the help of SEM.The results of the water absorption further demonstrate the binding of the interface between the CSF and the PP matrix.The results showed that CSF treated with 10 wt%NaOH is harmful and damage the mechanical properties of the composite.The wetting of the CSF in the PP is improved with the addition of a complex compatibilizer(5%MAPP+5%CS).The formation of a chemical bond between the fiber and the matrix result in enhancing the interfacial compatibility between the fiber and the matrix.Compared with pure PP(51.56 MPa),the flexural strength of 15-UT-5MAPPCS(63.14 MPa)and 15-UT-5MAPPCS(69.35 MPa)increased by 22.5%and 34.5%,respectively.The complex compatibilizer can replace alkaline treatment process to improve the mechanical properties of the composite.(3)In this study,CSFs were used as a reinforcing phase to improve the mechanical properties of WPC.The primitive CSFs were subjected to a short alkali treatment in a low alkali solution to expose the cellulose fibers.Alkali-treated CSFs(AT-CSFs)were cross-linked modified with chitosan and glutaraldehyde.Then,untreated corn stalk fibers(UT-CSFs)and cross-linked modified corn stalk fibers(CL-CSFs)were added with different contents(10 wt%,20 wt%,30 wt%,40 wt%),respectively.The mechanical,morphology,thermal and the water absorption behaviours of WPC were investigated in detail.The results indicated that crosslinking modification is an efficient method to improve the mechanical properties of WPC.Compared with UT-CSFs,the crystallinity index(CrI)of CL-CSFs was increased from 33.8%to 39.5%.The flexible transparent polymer layer on the surface of CL-CSFs could be observed by SEM.The addition of 40 wt%CL-CSF promoted an increase in flexural strength of 19.2%and an increase in flexural modulus of 8.3%compared to composite reinforced by UT-CSF.The addition of 20 wt%CL-CSF has an impact strength of 12.053 KJ/m~2,and the cross-linking modification promotes the impact strength of the composite to increase by 17.5%.The moisture absorption of the composites reinforced by CL-CSFs was lower than the composites reinforced by UT-CSFs.Compared with sample 40UT-CSF,The water absorption of the sample40CL-CSF decreased from 2.38%to 2.08%at 16 days.