Preparation And Properties Of Fiber Reinforced Polylactide Composites

To improve the environmental pollution and greenhouse gas emissions caused by traditional petroleum-based composites,it is an inevitable trend to actively develop renewable and biodegradable polymer materials under the background of building a new"double cycle"development pattern in China.Polylactic acid（PLA）,as a kind of biodegradable material,has excellent biocompatibility,biodegradability,and thermoplastic processability.However,the brittleness of PLA limits its application,making its application in related fields far behind traditional polymer materials such as polystyrene（PS）,polypropylene（PP）,and PET.For improving these shortcomings,high strength and high modulus PVA fibers and PLA fibers were used to prepare PLA based fiber reinforced composites through different processing methods.The structure,performance,and relationship between them were analyzed and studied to improve the mechanical properties of the composite and expand its application range.The main research contents and conclusions of this paper are as follows:（1）The PLA composites（PVAF₄-FRPs）reinforced by PVA fibers（PVAF₄）with high-strength and high-modulus were prepared by melt extrusion and hot pressing method.There is good interfacial bonding between PVAF₄ and PLA matrix,but an obvious agglomeration of PVAF₄ will appear if the content is higher than 20%.Meanwhile,with the increase in PVAF₄content,the tensile modulus and flexural modulus of PVAF₄-FRPs increased by 43.5%and38.6%respectively compared with pure PLA materials.The tensile strength and bending strength of PVAF4 FRP materials were improved by 5.2%and 13.9%respectively compared with pure PLA materials.（2）The PLA composites(PVAF₅₁-FRPs)reinforced by PVA fibers(PVAF₅₁)with high-strength and high-modulus were prepared by fiber carding,needle punching,and hot pressing.The PLA/PVAF₅₁ needle punched nonwovens prepared by the needle punching process have high consistency in appearance,and the internal fibers are arranged disorderly and mixed uniformly.Meanwhile,there is little difference between longitudinal and transverse tensile strength.It can be used as a prefabricated for preparing PVAF₅₁-FRPs.Under the hot pressing pressure of 5 MPa,when the hot pressing time is 5 min and the hot pressing temperature is190℃,the comprehensive tensile mechanical properties of PVAF₅₁-FRPs are optimal.With the addition of PVAF₅₁,the longitudinal and transverse tensile properties and flexural properties of pure PLA materials are greatly improved.When PVAF₅₁ content was 50%,the longitudinal and transverse tensile properties of PVAF₅₁-FRPs were 154 MPa and 152 MPa,respectively,which were 3.2 and 3.1 times higher than those of pure PLA materials.When the content of PVAF₅₁ is 60%,the bending strength is 134 MPa,which is 2.3 times of pure PLA material;The bending modulus reaches 6.9 GPa,3.4 times that of pure PLA material.（3）For further preparing fully biodegradable composites,PLA self-reinforced composites（L-SRCs）with different fiber content were prepared in two ways.One is that fiber carding,needle punching,and hot pressing.Another is that film and needle punched nonwoven laminating and hot pressing.They are PLA self-reinforced composites（SL-SRCs）with fixed fiber content,high fiber content PLA self-reinforced composites（HL-SRCs）and low fiber content PLA self-reinforced composites（LL-SRCs）.A comprehensive comparison shows that SL-SRCs made from bicomponent core-sheath PLA fiber by carding,needle punching,and hot pressing have the best mechanical properties.When the hot pressing temperature is 130℃,the tensile strength and bending strength reach the maximum,which are 62 MPa and 158 MPa respectively.The average peel strength of SL-SRCs（recorded as un-SL-SRCs）prepared by direct hot pressing with needle punched molding is significantly higher than that of SL-SRCs prepared by hot pressing after lamination.When the hot pressing temperature is 130℃,the average peel strength of un-SL-SRCs is the largest,1.3 k N/m,2.2 times that of SL-SRCs under the same conditions.The bicomponent core-sheath PLA fiber was added with the same reinforcement fiber as the core fiber.HL-SRCs were prepared by the method of fiber carding,needle punching,and hot pressing.When the content of reinforcement fiber was up to 80%,the tensile strength was still 49 MPa,the elongation at break was up to 29%,and there was little difference in longitudinal and transverse mechanical properties.The breaking elongation of LL-SRCs prepared by lamination hot pressing of film and needle punched nonwovens was significantly higher than that of pure PLA90 materials.When the content of reinforced fiber is60%,it reaches the maximum,34%,which is 9.7 times higher than that of pure PLA90 material.