Preparation and hydrophilic properties of star-shaped PLLA-PEG block copolymer fiber membranes
Polylactic acid(PLA)is an important biodegradable polyester material with good biocompatibility,low toxicity,and good mechanical properties.Its main raw material is starch fermentation in plants,which is renewable and can be degraded by microorganisms(bacteria,fungi,etc.)in nature.As a raw material for plant photosynthesis,PLA enters the natural cycle.There is great potential for application in fields such as green plastics,tissue scaffolds,and biomedicine.However,PLA has poor hydrophilicity and a long degradation cycle,which limits its application in many aspects.So pure PLA materials can no longer meet the growing demand,and modifying them has become a trend.The chemical modification of PLA mainly involves copolymerization with biodegradable substances to form linear or star-shaped copolymers.Research has found that compared to linear copolymers,star-shaped copolymers have smaller fluid mechanical volume and lower viscosity,indicating better thermal and degradation performance.In addition,plasticizer modification can be targeted at the performance modification of polymers to expand their application fields.Generally,it will choose to copolymerize with hydrophilic substances,such as the commonly used polyethylene glycol(PEG),which can be dissolved in interstitial fluid in the human body,and PEG with molecular weight below 4,000 can be quickly eliminated from the body without any toxic and side effects.The addition of PEG can effectively increase the chain mobility of PLA,improve its ductility and stretchability,and thus broaden the potential application range of PLA.To study the preparation process and hydrophilicity of star-shaped PLA multi block polymers,pentaerythritol(PET)was used as the initiator and stannous octanoate(Sn(Oct)2)as the catalyst.Star-shaped hydroxyl terminated poly(L-lactide)(s-PLLA)was prepared through ring opening polymerization(ROP),and condensed with polyethylene glycol(PEG,relative molecular weight is 1,000)to obtain four arm star-shaped poly(L-lactide)acid polyethylene glycol copolymers(s-PLLA-PEG).The s-PLLA-PEG fiber membrane was successfully prepared by electrospinning,and its surface morphology and hydrophilicity were tested and analyzed.A series of characterization methods were used to confirm the effective synthesis of polymers such as s-PLLA and s-PLLA-PEG.There are currently few reports on the research of PLA-modified fiber membranes.The results show that the melt temperature and glass transition temperature of s-PLLA-PEG decrease,and the flexibility is improved;the contact angle between s-PLLA fiber membrane and water is 132.10°,while the contact angle between the s-PLLA-PEG fiber membrane and water is 84.10°.Over time,the contact angle gradually decreases,and ultimately water is completely absorbed by the fiber membrane,exhibiting stronger hydrophilicity.Research has shown that when PEG is successfully grafted onto s-PLLA,the hydrophilicity of s-PLLA-PEG fiber membranes is significantly better than that of s-PLLA fiber membranes.This indicates that the presence of PEG can effectively improve the hydrophilicity and hydrophobicity of the surface of the s-PLLA fiber membrane,transforming it from a hydrophobic substance to a hydrophilic substance.Due to the excellent hydrophilicity of the s-PLLA-PEG fiber membrane,it has shown certain application prospects in medical dressings.
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