Preparation Of Polylactide/sisal Fibers Biocomposites Via In-situ Reaction Processing And Investigation On Its Structure And Properties

Due to environment and sustainability issues,this century has witnessed remarkable achievements in green technology in the field of materials science through the development of biocomposites.The development of high-performance materials made from natural resources is increasing worldwide both in academic research and industrial application,for their low cost,light weight,ability to recycle,good structural properties,and green degradable.The interfacial adhesion of polymer composites is of vital importance to the mechanical properties of composites.The natural fibers,as a kind of biologic material,possess much hydroxyl in the surface,which result in the interfacial compatibility between natural fibers and matrix in natural fiber reinforced polymer(NFRP)is generally poor due to the hydrophilic nature of natural fiber and the hydrophobic nature of polymer matrix.In this study,polylactide(PLA)and sisal fibers(SF)are used to fabricate bio-based natural fiber-reinforced polymer composites via in-situ reaction processing.Base on the reactivity of PLA molecular chain end group and hydroxyl on sisal fiber surface,the reaction materials system and processing conditions are designed to realize the in-situ interfacial reaction compatibilization of composites during melt-processing.By this method,the PLA molecular chain can be bonded on the fiber surface,therefor the interfacial tension can be decreased and the interfacial interaction of fibers and matrix can be improved.In addition,the chemical reactive third-phase components are introduced into PLA/SF composites,to combine the in-situ reaction compatibilization of composites and the reaction toughening of PLA matrix.Therefore,it can simultaneously realize improving interfacial adhesion between sisal fibers and matrix,and toughening of composites,by which good mechanical composites can be obtained with balanced stiffness-toughness properties.In this study,four reaction materials system are designed,that are TGIC composites system,EGMA composites system,ADR composites system and PBAT-ADR composites system,basing on three reaction components,which are organic reactive micro-molecule compounds,organic reactive macromolecule and reactive functionalized oligomer,respectively.The interfacial reaction,micro-phase structure,crystallization behavior,rheological behavior,glass transition,thermal degradation behavior and mechanical properties of composites are characterized and analyzed,by which the interfacial properties and the structure-property relationship of composites can be evaluated.The effects of improved interfacial interaction on the crystallization,dynamic rheological behavior,glass transition and thermal degradation behavior of PLA/SF composites were investigated.In turn,the change of structure and behaviors of composites can also reflect the mobility situation or ability of molecular chain and segment,thus reflect the change of interfacial interaction of composites.This is the idea of how to analyze the structure and properties of composites.Basing on the knowledge of the mobility of polymer chain and segments,the structure-property relationship of composites are demonstrated from the respect of molecular movement.At the same time,in three-phase structure composites,the combination of the in-situ reaction compatibilization of composites and the reaction toughening of PLA matrix result in complicated phase structure of composites,which is also one of the key-point of this study.By means of reaction materials system design,optimize of processing conditions,characterize of structure and properties of composites,the following main results and conclusions are obtained:1)The chemical bonding of PLA matrix with sisal fibers is realized via in-situ interfacial reaction processing.Therefore,the interfacial adhesion or interfacial interaction between fibers and matrix is significantly improved.2)Via investigation of crystallization behavior and rheological behavior of composites,it is found that the improved interfacial interaction of reaction-processed composites restricted the mobility of PLA molecular chain and segments.The sisal fibers act as physical-crosslinking point in composites melt,which improve the viscoelastic response and restricted molecular/segments mobility.These results were further demonstrated by the activation energies of glass transition relaxation(?E_a)of composites,which were calculated via dynamic mechanical analysis.3)The mechanical properties of reaction-processed composites are improved because of enhanced interfacial bonding strength.It is found that the stiffness of composites is notably enhanced,reflecting improved fiber reinforced effect.For the reaction toughening three-phase structure composites,composites with a good mechanical stiffness-toughness balanced property to obtain,improving the toughness of PLA/SF composites without much decline of tensile strength.Meanwhile,it is found that part of“soft”toughening phase tend to weld on the fiber surface,which was called self-weld fiber structure.The formation of this structure contributes to obtain stiffness-toughness balanced composites materials.4)By analyze of the thermal degradation behavior of composites,it is found that the heat resistance of reaction-processed composites is improved via enhanced interfacial adhesion.5)At the same time,there have much difference among the designed four reaction-processing composites system in micro-structure,behaviors and properties of materials.By the investigation of this study,the results show that using reaction processing technology,combine with materials design can realize in-situ reaction interfacial compatibilize of natural fiber reinforced polymer composites,and can regulate the structure and properties of composites.