| Polylactic acid(PLA)is a biodegradable polyester.Its waste is decomposed in nature to obtain carbon dioxide and water,which will not seriously pollute the environment.It is internationally recognized as an environmentally friendly substance.Polymerized rosin(PR)is a dimer of small molecule rosin with tricyclic diterpene structure,which is a green,renewable and degradable chemical raw material.Although PR is not a polymer material,it has special heating and softening characteristics,and is widely used in chemical processing,electronic engineering,food engineering and other related fields.Applying PR to the processing of PLA can expand the processing methods and application fields of PLA products.However,there are few reports on the blending properties of PR and PLA,and the methods and mechanisms of blending processing.In this paper,the blending process of PLA and PR was simulated by molecular dynamics for the first time,and the compatibility of PLA and PR with different blending ratios in the molten state was investigated.By analyzing the interaction parameters of Flory Huggins,it was found that when the mass fraction of PLA in the blend system was 40%,50% and 70%,the compatibility between PLA and PR was the best.In the process of blending PLA and PR,the value of the radial distribution function between molecules of different substances is greater than that of the same substance,indicating that the two substances have a certain compatibility.The simulation results of mean square end distance show that the higher the temperature is,the greater the degree of molecular chain disentanglement is,and the better the blending effect of the two substances is.With the increase of PR mass fraction in the system,the potential energy of the system first increases and then decreases.When the PR mass fraction is 50%,the potential energy of the system reaches the maximum,which indicates that the PLA molecular chain has the largest tensile degree,the best compatibility,and PR molecules are most evenly distributed between PLA molecular chains.With a small amount of PR,PLA can be induced into fibers,and micro nano scale PLA fibers can be continuously prepared on a small scale in conventional melt spinning equipment.The spinning temperature of the blend system was determined to be 190 ℃ by thermogravimetric analysis,and the rheological properties of the two substances were emphatically studied.The rotational rheological test results proved that the rigid small molecules of PR could penetrate into the PLA molecular chains during the spinning process.With the increase of PR content in the blend system,PR continued to promote and guide the flow of PLA,leading to the enhanced system fluidity.The results of melt spinning pilot study show that the method of PR inducing PLA micro nano fiber has certain industrial feasibility.The crystallinity reached 75.3% when PR content was 50% by differential scanning calorimetry.Melt spinning test and electron microscope test verified that 50% PR and PLA were melt spun to form micro nano fibers with a diameter of up to 400 nm.Solution casting is also a processing method of PLA.By changing the surface morphology of the membrane and attaching low surface energy substances to the surface,super hydrophobic self-cleaning PLA membrane can be obtained.The existing hydrophobic finishing is difficult to achieve the superhydrophobic effect of 150 ° contact angle,and the hydrophobic effect is difficult to last long,and often weakens rapidly after use.In this subject,PLA micro nano porous membrane with high surface roughness was prepared by using renewable biodegradable rosin derivatives as porogen,and then octadecyl trichlorosilane was used for nano coating to obtain PLA hydrophobic membrane with durable hydrophobicity and self-cleaning function.According to the surface element analysis,siloxane can be evenly distributed on the film surface,and the porous film with 60% and 70% PLA in the mixed system can provide good adhesion for siloxane.The study of surface hydrophobicity and self-cleaning performance shows that the water contact angle of PLA membrane is 150.6 ° at the highest,which has self-cleaning function.After five high strength friction cycles,the water contact angle of PLA hydrophobic membrane remained above 120 °,which proved that the durability of self-cleaning effect could be significantly improved by increasing the nano level roughness of PLA porous membrane surface. |
