Optimal Preparation And Properties Of Cottonseed Protein/Sisal Fibers Composites

In order to protect the environment and use resources more reasonably,researchers use waste cottonseed protein to transform it into an eco-friendly green material.The plastics made of pure cottonseed protein have the problems of low mechanical strength,poor water resistance and poor thermal stability.Aiming at improving these problems,we use oriented long natural sisal fiber as reinforcing phase and dialdehyde starch?DAS?as cross-linking agent.The effects of different contents of DAS on the mechanical properties and thermal stability of cottonseed protein/sisal fiber were investigated in this paper.We also explore the interfacial binding mechanism between DAS,cottonseed protein and sisal fiber.Our main results are as follows:?1?Based on the raw material cottonseed protein?50%protein content,abbreviated as CP?,we got CP/SF green composite plastics with different DAS contents by CP urea denaturation,DAS cross-linking,glycerol plasticization which also needed hot-pressed with unidirectional and uniformly arranged sisal fiber?SF?obtained by prepreg.The mechanical properties test showed that the introduction of 5wt%SF increased the mechanical strength of cottonseed protein matrix?fracture stress increased from 0.35MPa to 1.28MPa?.With the addition of DAS,the toughness of CP/SF composite plastics is improved.Among them,20wt%DAS crosslinked CP/SF composite plastics show better mechanical strength?fracture stress is7.55MPa?,higher thermal stability and glass transition temperature,which is due to the stable network cross-linking structure between DAS and CP/SF and the hydrogen bonding interaction between CP and SF.In addition,the results of SEM and FT-IR show that 20wt%DAS has better compatibility with CP and SF.Moreover,the formation of imine bond(1652cm^-1)indicates that there was a good cross-linking effect between DAS and CP/SF.The fiber control tests show that the fiber composite processing method of oriented arrangement and pre-impregnation is the key to improve the mechanical strength of cottonseed protein plastics.?2?In order to reduce the effect of impurities such as ash on cottonseed protein matrix and further explore the interface binding mechanism between DAS,cottonseed protein and fiber,the CP was purified to obtain purified cottonseed protein?PCP?with protein content of74.2%.Using PCP as raw material,a series of DAS crosslinked PCP/SF films with different contents were obtained by casting and prepreg SF?maintaining fiber orientation?.The results of FT-IR and ¹³C NMR show that DAS forms the interaction mechanism of protein-protein cross-linking and protein-fiber chemical interface adhesion by forming imine bond with PCP and ester bond with SF.Thus,the stability between DAS,PCP and SF is maintained,and the PCP-based film is improved.The test results of properties show that the 20wt%DAS crosslinked PCP/SF films has higher mechanical strength,better water resistance and higher thermal stability.Moreover,the films'fracture stress,water absorption and thermal degradation residual rate?600??reach 21.0MPa,38.41%and 27.56%,respectively.In this study,a series of DAS crosslinked cottonseed protein/sisal fiber composites were obtained.This kind of composite material is expected to be used in food packaging and other fields.