Preparation And Property Study Of PLA/ENR TPV Based On Reversible Bonds

Due to the threat of environmental pollution from petrochemical materials and the accelerated pressure of the earth's petroleum and fossil resources,the research and development of bio-based renewable materials has become a hot topic for the scholars around the world.The modification and reinforcement of bio-based renewable materials which represented by polylactic acid(PLA)and natural rubber(NR)have become the main content of bio-based renewable materials research.How to make the performance and processing of bio-based renewable materials adapting to the application conditions of modern industry and technology has always been a major problem that researchers have to face.Self-healing modification is a sustainable and resource-friendly modification method.Self-healing property gives the material the ability to repair wounds and defects,so it can greatly improve the service life and stability of the material.Combining bio-based renewable materials with self-healing properties to prepare a more sustainable renewable material is bound to alleviate the problem of environmental pollution and the pressure of resource shortage.In this thesis,epoxidized natural rubber(ENR)and carboxylated carbon nanotubes(SCNTs)were mixed,assisted by 2,2'-Dithiodibenzoic acid(DTSA)for vulcanization,and the ENR was processed by dynamic reversible bonds such as disulfide bonds,?-hydroxyester bonds,and hydrogen bonds.The research results show that S-CNTs were well dispersed in ENR.The carboxyl groups on S-CNTs could effectively react with the epoxy groups on ENR to form the?-hydroxy ester bonds.The degree of vulcanization of ENR increased with the increasing of SCNTs content.The addition of S-CNTs and DTSA enhanced the mechanical properties of ENR,for example,the tensile strength of the pure ENR was about 0.52 MPa,and the tensile strength of the sample with 15 phr S-CNTs and 0.5phr DTSA was increased to about 2.28 MPa,which was 4 times of pure ENR.At the same time,the ENR/S-CNTs composite rubber has excellent self-healing property.The self-healing efficiency of the sample with 5phr S-CNTs and 0.5phr DTSA reached 99.7% after healing at 80? for 8h.This is because there are a large number of dynamic reversible bonds inside the rubber,which can quickly repair breakages and wounds.According to the results of self-healing ENR,we further expanded the ENR/S-CNTs system to the thermoplastic vulcanizate(TPV)field,and obtained PLA/ENR/S-CNTs bio-based self-healing TPV.Through the dynamic vulcanization,we successfully mixed PLA with selfhealing ENR.Through scanning electron microscopy and transmission electron microscopy tests,we found that S-CNTs were mainly distributed in the ENR phase and interface between PLA/ENR,which effectively improves the compatibility of PLA and ENR.Through mechanical tests,we found that the mechanical strength of TPV increased significantly with the increasing of S-CNTs content.For example,the tensile strength of the P3E7S0.5 sample without S-CNTs was about 3.08 MPa,and the tensile strength of sample with 10 phr S-CNTs reached about 7.17 MPa,which was an increase of about 130%.In addition,PLA/ENR/S-CNTs TPV has a good self-healing ability.The addition of PLA does not greatly affect the self-healing performance of TPV.For example,the self-heal efficiency of sample with 1phr S-CNTs and0.5phr DTSA can also reach 99.7%.PLA/ENR/S-CNTs TPV also has a good shape memory function due to its co-continuous structure and the good compatibility between PLA and ENR enhanced by S-CNTs.In the twophase structure of TPV,the rubber phase can provide the resilience of the material to restore the shape,and the plastic can provide the fixing force of the material to fix the shape.The stress transfer between these two phases plays an important role in maintaining the shape of the material.Due to the high content of rubber in PLA/ENR/S-CNTs TPV,the shape recovery rate of all samples reached 100%,and the shape fixation rate gradually decreased with the increasing of S-CNTs content.This is because of the PLA content in TPV was low,it provided the shape fixing force was low,too.And the stronger the cross-linked network was,the more difficult the shape to be fixed.At the same time,TPV also had considerable shape reshaping ability.Under the high temperature,the shape of the samples could be changed,and the topological rearrangement of the internal cross-linked network could permanently maintain the shape of the TPV.