| High density polyethylene(HDPE)breathable membrane materials represented by Tyvek are commonly used as medical packaging consumables due to their excellent breathability,mechanical strength and chemical stability.HDPE has superior mechanical properties but is not degradable and has high recycling costs.In the context of consumer upgrading,the demand for medical packaging consumables in China is on the rise and the resulting packaging waste disposal problem needs to be solved.Polylactic acid(PLA)fiber membrane is a promising biodegradable polymer polyester packaging membrane material,but its mechanical properties are insufficient to limit the expansion and application of PLA fiber membrane in the packaging field,this paper first selects nucleating agent and plasticizer to strengthen and toughen the PLA raw material,and then prepares the PLA fiber membrane with excellent permeability by melt microfraction electrostatic spinning technology,and finally the overall mechanical strength of the fiber membrane is enhanced using a hot pressing process while maintaining a certain degree of permeability.The main research contents of this paper are as follows:(1)The internal structure of melt electrospun PLA membrane is loose,and it is easy to produce surface fiber detachment,slippage and deformation and other defects when subjected to force,which affects the application effect.A three-factor,three-level response surface experiment was designed using Design-Expert 11 software to optimize and validate the hot-pressing process parameters.The unidirectional average tensile strength of the PLA hot-pressing membrane produced under the optimal hot-pressing process parameters was27.613 MPa,which was 149.89% higher than that of the PLA membrane before hot-pressing.The modification methods used in the subsequent experiments are all melt blending physical modifications,which do not change the chemical properties of PLA materials,so the best hot-pressing process parameters of PLA are still used for the hot-pressing post-treatment of PLA/CH-S04 and PLA/CYD-T151 fiber membranes.(2)The mechanical strength of melt electrospun PLA fibers is low,and the mechanical strength can be improved by increasing the crystallinity of PLA,nucleating agent is an efficient modifier to improve the crystallinity of the material,so the organic inorganic composite nucleating agent CH-S04 enhanced modified PLA,this paper studied the non-isothermal crystallization and isothermal crystallization behavior of PLA/CH-S04,and found that the appropriate increase in spinning temperature and voltage can improve the crystallinity of PLA/CH-S04,and the crystallization rate of PLA/CH-S04 reaches the maximum at 110°C.The mechanism of CH-S04 in the multi-stage drafting process is analyzed,and it is found that the multi-stage drafting process is beneficial to improve the crystallinity of PLA/CH-S04,and the effect of CHS04 on the crystallinity of PLA is more obvious under the spinning process conditions of applied voltage and airflow assistance.The mechanical properties of PLA/CH-S04 fiber membrane/hot-pressed membrane were tested,and it was found that the addition of nucleating agent could effectively improve the tensile strength of PLA/CH-S04 fiber membrane/hot-pressed membrane(the maximum values were 12.33 and 34.97 MPa,respectively,which increased by11.58 and 26.64% compared with pure PLA).(3)Melt electrospun PLA fibers are less tough,can reduce the intermolecular chain interaction force by adding plasticizer to improve its toughness,so the choice of dendritic polymer plasticizer CYD-T151 toughening modified PLA,to explore the different CYD-T151 content and spinning conditions on the melt flow rate,fiber morphology and mechanical properties of the effect.The results show that the addition of CYD-T151 can effectively improve the melt flow rate of the blended system;when the content of CYDT151 is 1.25%,the spinning temperature is 240℃,and the spinning voltage is55 k V,the average fiber diameter of the spun fibers reaches 1.360μm,which is49.72% less than that of pure PLA,and the standard deviation of the diameter is 0.694,with uniform fiber diameter distribution;The tensile strength and elongation at break of the fiber membrane were 11.50 MPa and 92.33%,which were 4.07% and 13.99% higher than those of pure PLA,and the tensile strength and elongation at break of the hot-pressed membrane were 29.68 MPa and52.66%,which were 7.49% and 82.91% higher than those of pure PLA.(4)The hot pressing process increases the mechanical strength of the fiber membrane while decreasing its permeability,in order to investigate the effect of post-treatment measures on the permeability of fiber membranes,the permeability of PLA,PLA/CH-S04 and PLA/CYD-T151 fiber membranes/hotpressed membranes before and after hot-pressing were characterized.The results showed that the porosity and air permeability of the fiber membrane/hotpressed membrane decreased gradually with the increase of surface density,and the effect of surface density on the porosity of the hot-pressed membrane was more obvious,and the change of air permeability of the fiber membrane after hot-pressed treatment tended to level off when the surface density exceeded 35g/m2;the air permeability of the reinforced and toughened modified samples was tested and found that the air permeability of PLA/CH-S04 fiber membrane/hot-pressed membrane was higher than that of pure PLA under the same surface density conditions,and the air permeability of PLA/CYD-T151 fiber membrane/hot-pressed membrane was related to the average fiber diameter;the test values of the ventilation resistance of PLA fiber membrane at different surface densities were fitted and found to be positively correlated,and then the relationship between fiber fineness and theoretical ventilation resistance was obtained,and it was found that when the fiber diameter was uniformly distributed,the smaller the average fiber diameter was,the higher the theoretical ventilation resistance was.In summary,this paper prepared modified PLA high-strength breathable fiber membranes by melt microfraction electrostatic spinning technology and hot-pressing post-treatment process,analyzed the strengthening and toughening mechanism of nucleating agent and plasticizer on melt microfraction electrospun fiber membranes,and explored the influence law of spinning process and fiber morphology on mechanical properties and breathability of fiber membranes/hot-pressed membranes.The research content of this paper provides a technical exploration of melt microfraction electrostatic spinning in the field of high-strength breathable membrane preparation,and provides new ideas for the industrial production of PLA high-strength breathable membranes. |
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