Preparation Of PLA-based Degradable Waterborne Polyurethane And Construction Of Waterproof And Breathable Coating For Fabrics

Because the advantages of molecular structure flexibility,good fatigue resistance,flexibility and low VOC emissions,waterborne polyurethane(WPU)has been widely used in many fields such as coatings,adhesives,synthetic leather.However,the traditional WPU is prepared by petroleum products,which is difficult to degrade,leading to environmental problems such as plastic pollution and high CO2 emissions.In the context of "carbon peaking and carbon neutrality",people’s attention is grabbed by biodegradable materials due to its unique life cycle and reduction carbon emissions,which are important solutions to achieve the "carbon peaking and carbon neutrality" target.In this thesis,PLA diol and isophorone diisocyanate(IPDI)was used as main raw materials to prepare biodegradable WPU.And then,biodegradable WPU was modification by the functionalized modification of cellulose nanocrystals(CNC).Based on this biodegradable WPU,a kind of waterproof and breathable coating for fabrics were explored.The specific research content and results are as follows:Polyurethane prepolymer(PUNCO)was prepared from PLA diol,PCL diol and IPDI.The chain was extended by DMPA and BDO,and then after TEA neutralization and rapid emulsification PLA-based waterborne polyurethane(PLA-WPU)and PCL-based waterborne polyurethane(PCL-WPU)was prepared.PCL-WPU enhanced PLA-WPU(PLA-WPU-PCL)was prepared through physical blending PLA-WPU and PCL-WPU.The effect of the content of PCLWPU on the film property of PLA-WPU-PCL was investigated.The film was characterized by FT-IR,particle size analyzer,TGA,DSC,XRD,and composting at room temperature.The experimental results showed that when the mass ratio of PCL-WPU to PLA-WPU is 30:70,the comprehensive film-forming performance of PLA-WPU-PCL is the optimal.Compared with pure PLA-WPU and PCL-WPU,the crystallization property of PLA-WPU-PCL is obviously improved.Tensile strength increased 97%than PLA-WPU;The elongation at break increased by 13%compared with PLA-WPU;The initial thermal decomposition temperature is 290.5℃;The mass loss rate of the compost degraded at room temperature for 14 days is 1.8%.The initial degradation rate is slow,after 10 weeks,PLA-WPU-PCL can be degraded into low molecular weight fragments,and after 3 months,it is basically absorbed and consumed by microorganisms.3-aminopropyl triethoxysilane(APTES)was used to prepare aminated cellulose nanocrystals(N-CNC),and tetramethylpyridine(TEMPO)was employed to prepare carboxylated cellulose nanocrystals(C-CNC).Then,N-CNC and PLA-WPU composites(N-CNC/PLA-WPU)and C-CNC and PLA-WPU composites(C-CNC/PLA-WPU)were prepared by in-situ polymerization with IPDI as hard segment,PLA diol as soft segment and DMPA as hydrophilic chain extender,and the film was formed.The influence of the amount of surface functionalized CNC on the properties of PLA-WPU was explored.The film structure and properties of N-CNC and C-CNC were characterized by FT-IR,XRD,mechanical test,DSC and 14-day normal temperature composting degradation.The experimental results showed that both N-CNC and C-CNC can effectively improve the crystallization and mechanical properties of PLA-WPU,reducing the glass transition temperature of the composites as well as improving the composting degradation performance of the composites.The strengthening effect of C-CNC on PLA-WPU is obvious.When the content of C-CNC is 2%(based on the weight of WPU),the crystallinity of C-CNC/PLA-WPU composites has been obviously improved,the tensile strength is 15.6 MPa,the elongation at break is 516%,the Tg is 14.7℃,and the mass loss rate is 81.7%after composting at room temperature for 14 days,which exhibits good degradation performance.Using polypropylene meltblown fabric as the base and PLA-WPU-PCL30 as the impregnation slurry,a waterproof and breathable coating was constructed on polypropylene meltblown fabric through the combination of impregnation-spray method and wet solidification in the drying process.The effects of the solid content,viscosity and padding times of PLA-WPU-PCL30 on the micro-morphology,waterproof and moisture permeability of the coated fabric were studied.The blood puncture resistance and bacterial barrier property of the prepared waterproof and breathable fabric were tested,and the application of PLA-WPU-PCL30 in the field of medical protective clothing was explored.The experimental results showed that when the solid content of PLA-WPU-PCL30 is 15%,the viscosity is 600 mPa·s,and padding is performed for six times,the comprehensive properties of the coated fabrics is optimal.The 20～40 μm micropores are formed between the coated fabrics,the hydrostatic pressure resistance is 4061 Pa,and the water vapor transmission capacity is 1 751 mg/(10 cm2·24 h).Under these conditions,the blood puncture resistance of the fabrics is improved,and the bacterial barrier property is slightly reduced,which is expected to expand its application in the field of medical protective clothing.