Preparation And Properties Of The Ramie Fiber Reinforced Poly(Lactic Acid)Composites

Due to the severe environmental issues brought in the manufacturing and recycling process of the polymers and the fiber reinforced plastics,the bio-materials have been expected for wide application in engineering fields.Compared with the synthetic fiber composites,the bio-based composites reinforced with plant fiber have been concerned in the engineering fields,such as aerospace,automotive,construction,packaging,sports and medical due to their renewability,biodegradability,low cost,light weight,high specific strength and specific modulus.However,there are a lot of hydroxyl groups on the fibers surface which show strong hydrophilicity.Meanwhile,the bio-based polymer chains contain a large number of hydrophobic groups.The great difference of polarity results in weak interfacial adhesion between the fibers and polymer matrix which deteriorates the mechanical properties.In addition,the high flammability of the plant fiber composites greatly constrains the further application in engineering fields.Based on the above problems,in order to improve the comprehensive properties and broaden the engineering application of plant fiber composites.The ramie fiber reinforced poly(lactic)acid(PLA)composites were prepared in this study,and their mechanical properties,interfacial strength and halogen-free flame retardancy were investigated.Firstly,this study investigated the influence of the fiber loading on performance of the PLA/ramie fiber composites,including the heat deformation temperature,interfacial strength,crystallization behavior,rheological behavior and mechanical properties.The results indicated that the heat resistance of the composites was improved with the increasing fibers.Especially,the heat deformation temperature of the composites improves from 51.6? to 57? when blending the fiber of 40 wt%.However,there were numerous fibers pull-out and holes in the fractured surface due to the poor interfacial adhesion between the fibers and PLA.There were fiber agglomerations because of the poor wettability between the fibers and PLA when introducing the high fibers loading(40 wt%).Differential scanning calorimetry showed that the fibers restricted the movement of PLA molecular chain and promoted the formation of the perfect crystal due to physical joint effect.At the same time,the storage modulus,loss modulus and composite viscosity of the composites were improved with the increasing fibers loading.The tensile and flexural strengths of the composites were improved with the increasing fiber loading.Compared with PLA,the tensile strength and bending strength of PLA/40RF composite enhanced by 22.9%and 21.9%,respectively.Secondly,the ramie fiber composites were manufactured by adding the riglycidyl isocyanurate(TGIC)and treating fiber with silane,NaOH,and NaOH+silane treatment.The results indicated that there were numerous impurities on the unmodified ramie fiber,which were removed after surface treatment.PLA molecular chain was bonded on the fibers surface when blending the treated fibers and TGIC,which enhanced the interaction ability between the fibers and PLA.Therefore,there were numerous fibers were pulled out from PLA matrix,and the cracks at the interface and voids were formed.Especially for TGIC,the storage modulus,loss modulus and complex viscosity of PLA/RF/TGIC composite were significantly improved.In addition,the tensile and flexural strengths were greatly enhanced by the treated fibers and TGIC.Especially compared to pure PLA,the addition of untreated fibers and TGIC in PLA increased the tensile and flexural strengths by 49.8%and 46.5%respectively,and the impact strength was almost the same as PLA.Finally,the effects of halogen-free flame retardant systems(AlPi,MCA and SiO2)on comprehensive performance of ramie fiber reinforced poly(lactic acid)composites were investigated,including the flame retardancy,thermal behavior,mechanical properties and combustion behavior.The addition of MCA contributed to improve the tensile strength.Especially for flame retarded composites with individual or two flame retardants,the tensile strength was enhanced with increasing MCA.The tensile strength of PPR/3M composite raised by 88.37%compared to RRP/3A composite.The incorporation of flame retardants was not almost effect on the tensile modulus.Moreover,the UL-94 rating and limiting oxygen index(LOI)were improved by blending flame retardants.Especially,the RRP/AM,RRP/A2MS and RRP/AMS composites reached UL-94 V-0 rating,and the corresponding LOI fulfilled 34.4%,31.6%and 30.1%,respectively.Meanwhile,the flame retardants also increased the peak of heat release rate(p HRR)and total heat release(THR).Compared with RRP composite,the p HRR and THR of RRP/AMS composite lowered by 22.5%and 15.0%,respectively.The excellent flame retardancy resulted from the formation of high-quality char layers,the chain reation of free radicals and the dilut effect of inert gases during combustion.