Reinforcement And Toughness Of Bamboo-Fibers/Unsaturated Polyester Composites

To improve the interfacial adhesion between bamboo fibers(BFs)and unsaturated polyester(UPE)resins,BFs were treated with a copolymer of acrylated epoxidized soybean oil(AESO)and 1,6-diisocyanatohexane(DIH),i.e.AESO-DIH,and 1,2-epoxy-4-vinylcyclohexane(EVC),respectively.The UPE resins were incorporated with acetoacetoxyethyl methacrylate(AAEM)to improve the toughness of the resins.The surface chemistry of BFs was investigated using FT-IR,XPS and NMR analyses.The BF reinforced UPE composites were prepared by compression molding.The dynamic and static mechanical properties,and water absorption of the BF/UPE composites were evaluated.Scanning electron microscope(SEM0 was used to further reveal the fracture morphology and thus the interfacial adhesion of the composites.The conclusions were drawn as follows:(1)The tensile strength(TS),flexural strength(FS),and flexural modulus(FM)of the BF/UPE composites were significantly improved after the treatment of BFs with AESO-DIH.When the usage of DIH was 5 wt%of the dried-weight of BFs,the increments of 38.88%,29.06%and 47.50%were obtained in the FS,FM and TS of the modified-bamboo fibers composites when compared to the control,respectively.(2)The TS,FS and FM of the BF/UPE composites were significantly improved by the treatment of BFs with EVC,but the impact strength(IS)of the composites decreased when the fibers were treated by EVC with a usage of more than 5 wt%based on the weight of bamboo fibers.When the usage of EVC was 3 wt%,the composites obtained the optimal mechanical properties;the TS,FS and FM of the modified-fibers reinforced composites were 23.76%,12.14%,and 18.95%higher than those of the untreated-fibers composites,respectively.(3)The incorporation of AAEM significantly increased the toughness of UPE resins and the IS of the resultant BF/UPE composites.When the AAEM usage was 10 wt%of the UPE reins,the AAEM-treated composites had 15.53%higher IS than the composites without the addition of AAEM.However,the incorporation of AAEM did not significantly change the TS,FS and FM of the composites.(4)The FT-IR spectra of the untreated and AESO-DIH-treated BFs showed that the isocyanate groups(-NCO)of DIH react with the hydroxyl groups(-OH)of both BFs and AESO,generating a carbamate structure,i.e.,the AESO-DIH was successfully grafted onto the surface of BFs.(5)XPS analysis indicated that the spectra of AESO-DIH-treated BFs had a nitrogen signal and two new peaks(C5 and C6 bonds)which correspond to the carbons from C-N and O-C=N bonds,respectively.In addition,the treatment of BFs with AESO-DIH resulted in the increase of C=O/O-C=O and O-C=O contents,demonstrating that AESO-DIH was grafted onto the surface of BFs.The relative contents of Cl(C-C,C-H)and O2(C-O-H/C-O-C)significantly increased after the modification of BFs with EVC,which was ascribed to the linkage formed by the reaction between EVC and-OH groups of BFs.(6)The NMR spectra of BFs showed two new characteristic signals of the treated-fibers,which correspond to the carbons from N-C=O and C-N bonds of the urethane linkages among DIH,AESO and BFs.Meanwhile,the characteristic signals of AESO molecules also appeared in the spectra of the treated BFs.These results indicated that AESO-DIH was covalently bonded onto the BFs surface.(7)DMA analysis showed that the modification of BFs significantly improved the storage modulus of the BF/UPE composites,and that the incorporation of AESO might increase the molecular mobility and cause energy dissipation at the interface of the composites due to the soft molecular chains of AESO,thus increasing the damping parameter of the composites.The EVC treatment of BFs obviously improved the glass transition temperature(Tg)and storage modulus whilst reducing the damping parameter of the resultant composites.With the incorporation of AAEM,the damping parameter of the composites significantly increased,indicating that the stifness and thermal stability of the composites decreased.(8)It was found that both AESO-DIH and EVC treatments significantly decreased the water uptake rate and diffusion coefficients of the BF/UPE composites.(9)SEM analysis revealed that the interface adhesion of the BF/UPE was improved after the treatment of BFs with AESO-DIH and EVC,respectively.The incorporation of AAEM into UPE resins also improved the interface bonding of the composites.