Research On Mechanical And Thermal Properties Of Energy-Saving And Environmental Jute Fiber/Polypropylene Composites

Driven by the dual goals of carbon neutrality and carbon peaking and the green development of the vehicle industry,new requirements and challenges have been put forward for vehicle materials.Natural bast fiber composite is a green 、 lightweight material with a series of advantages such as,low density renewable and biodegradable.However,natural bast fibers are hydrophilic and have poor interfacial compatibility with hydrophobic resins,resulting in poor mechanical properties of the composite.Moreover,the application of such composites in delivery vehicles requires heat resistance and thermal dimensional stability.A complete investigation and evaluation of the composites’ mechanical and thermal properties is urgently required to expand the application of such green composites.A novel jute fiber/polypropylene composite(JF/PP)was prepared with jute fiber as the reinforcement and its surface hydrophobic alteration in this work to further broaden the applicability of bast fiber composites in the automotive field.The effects of jute addiction and fiber treatment on the mechanical performance of JF/PP composites,as well as thermal properties such as heat distortion temperature(HDT)、coefficient of linear thermal expansion(CLTE),and the corresponding mechanism of action,are investigated in this work.The compatibility and interfacial bonding strength in between the modified and non-modified fiber and PP matrix were analyzed by contact angle test and SEM images.The main research contents of this article are as follows:(1)A new kind of modified jute fiber reinforced polypropylene composites(modified JF/PP)with fiber content in range of 10-25wt% was fabricated by a hybrid technique of mill mixing and injection molding process,in which the jute fiber was modified with amino silicone oil(ASO)invented by our research group in the present work.This study enriches and expands the broad category of plant fiber-reinforced resin-based composites.(2)The effect of fiber content on the mechanical properties of the modified JF/PP composites was studied and compared with the unmodified JF/PP in this study.The results indicated that the tensile strength and flexural strength of JF/PP composites increased with the increase of fiber content,while the impact strength decreased.The mechanical properties of the modified JF/PP composites were better than those of the unmodified composites with the same fiber content.The compatibility and interfacial bonding strength in between the modified and unmodified fiber and PP were analyzed by contact angle testing and SEM.The results showed that the ASO emulsion modification changed the surface properties of jute fibers from hydrophilic to hydrophobic and enhanced the interfacial bonding between the fibers and the resin,thus significantly improving the mechanical properties of the modified JF/PP materials.It demonstrated that ASO emulsion treatment is an effective method to improve the mechanical properties of jute fiber-reinforced resin matrix composites.(3)The effect and the related mechanism of action of fiber content and ASO emulsion treatment on the heat resistance of JF/PP were investigated.The results showed that HDT of JF/PP increased with the increase of fiber content.The HDT of JF/PP composites before and after modification reached 142.5 °C,which was 53.5% higher than that of pure PP.From the analysis of DSC,it is clear that the addition of jute fibers can promote PP heterogeneous nucleation and limit the motility of molecular chain segments in the amorphous region of PP,thus improving the heat resistance of JF/PP.The modification of ASO emulsion enhanced the interfacial bonding between the fiber and resin,and the fiber had a stronger restriction effect on the movement of molecular chains in the amorphous region of PP,which further improved the heat resistance of the composites.Therefore,the HDT of the modified JF/PP were all higher than those of the unmodified composites with the same fiber content.(4)The effects of fiber content and ASO emulsion treatment on the thermal dimensional stability of JF/PP composites were compared and analyzed.It was found that The CLTE of the JF/PP composites showed a decreasing trend with increasing fiber content,indicating that the thermal dimensional stability of the JF/PP composites improved.Compared to pure PP,the CLTE of the composites at 25wt% content decreased by 73.2% in the flow direction and by 14.4% in the vertical flow direction,showing anisotropy.The ASO emulsion modification improved the interfacial bonding of the composites and further impeded the thermal motion of PP molecular chains,which made the modified JF/PP have higher thermal dimensional stability than the unmodified composites.The results indicate that increasing the fiber content and the modification of ASO emulsion are important ways to improve the thermal dimensional stability of jute fiber composites.This study is expected to provide effective guidance for developing low-carbon,energy-efficient,high-performance fiber-reinforced resin matrix green composites and expanding their applications in the field of delivery vehicles.