废旧聚对苯二甲酸乙二醇酯纤维醇解制备阻燃水性聚氨酯及其应用

Preparation and application of flame retardant waterborne polyurethane by alcoholysis of waste polyethylene terephthalate fiber

为解决废旧聚对苯二甲酸乙二醇酯(PET)纺织品日益增多,造成巨大的能源和资源浪费问题,采用醇解法对PET纤维进行解聚,优化其解聚工艺;并以醇解产物为原料合成磷硅协同阻燃改性水性聚氨酯,探究了异佛尔酮二异氰酸酯中NCO基团与对苯二甲酸双羟乙酯中OH基团的量比(n(NCO)/n(OH))、阻燃剂三羟甲基氧膦(THPO)和二氧化硅(SiO_(2))质量分数对阻燃改性水性聚氨酯形态和稳定性的影响;然后将得到的阻燃改性水性聚氨酯通过后整理的方法改性PET织物,并表征其阻燃性能。结果表明:在乙二醇(EG)为解聚剂,酯酸锌和氯化胆碱为催化剂的条件下,最佳解聚工艺为EG与PET质量比为4∶1、氯化胆碱与酯酸锌量比为1∶1、反应温度为185℃、反应时间为4 h,解聚产物对苯二甲酸双羟乙酯的产率可达87.6%;当THPO质量分数小于24%,SiO_(2)质量分数小于6%,n(NCO)/n(OH)在3~7时,阻燃改性水性聚氨酯呈均匀稳定的乳液形态;当THPO质量分数为24%,SiO_(2)质量分数为4%,n(NCO)/n(OH)为6时,阻燃改性PET织物具有较高的阻燃性能,残炭率可达13.9%(比原PET织物的残炭率提高127%),极限氧指数最高达29.7%,垂直燃烧测试达V-0级。

Objective The increasing amount of waste polyethylene terephthalate(PET) textiles has resulted in a huge waste of energy and resources. Due to the limitation of recycling methods, the reuse of recycled products is also affected. In order to improve the yield of waste PET fabric and to reuse the recycled products, the aim of this research is to optimize the reaction conditions for depolymerization of waste PET fabric, to synthesize, using the depolymerized product as raw material, stable waterborne polyurethane(WPU), and to conduct flame retardant modification of the waterborne polyurethane for flame retardance.Method Under the conditions of choline chloride and zinc acetate as catalysts, glycolysis was used to depolymerize waste PET fabric. The effects of reaction time, catalysts content and other influential factors were investigated on the product yields, and the products were characterized using Fourier transform infrared spectro-meter(FT-IR). Waterborne polyurethane was synthesized by the alcoholysis product ethylene terephtha-late(BHET) and isoflurone diisocyanate(IPDI) and so on, and tris(hydroxymethyl)phosphine(THPO) and SiO_(2)were used to improve its flame retardant property. The conditions were optimized for making stable waterborne polyurethane emulsion, and the effects of initial n(NCO)/n(OH), content of the flame retardants and SiO_(2)on the flame retardant property of WPU were systematically studied, and characterization was carried out using FT-IR and thermal gravity analysis. Flame retardant modified waterborne polyurethane on PET fabrics was studied with the assistance of scanning electron microscope(SEM).Results The best depolymerization process took place when the mass ratio of EG and PET was set to be 4∶1, molar ratio of choline chloride to zinc acetate 1∶1, reaction temperature 185 ℃, and reaction time 4 h. The FT-IR results indicated that the depolymerized product was bis(hydroxyethyl) terephthalate(BHET), whose yield was up to 87.6%. When the THPO content was less than 24%, the SiO_(2)content less than 6%, and the n(NCO)/n(OH) was 3-7, the flame retardant modified waterborne polyurethane formed a uniform and stable emulsion. When the THPO content was 24%, SiO_(2)content was 4%, and n(NCO)/n(OH) was 6, the flame retardant modified PET fabric demonstrated promising flame retardant properties, with the residual carbon rate reaching up to 13.9%, which is 127% higher than original PET fabric, and the LOI value of the modified PET fabric reached up to 29.7%, which meets UL-94 V-0 level. The SEM results suggested that the PET fabric was uniformly coated by the flame retardant modified polyurethane emulsion after treatment, and the voids between the fabric and yarns were filled by the polyurethane, and the emulsion and the fabric were integrated together.Conclusion This research has led to the following achievements: 1) waste PET fibers are depolymerized via alcoholysis;2) the depolymerized product are successfully synthesized into flame retardant modified waterborne polyurethane;3) the flame retardant modified waterborne polyurethane is used to treat PET fabrics which demonstrate promising flame retardant performance. The route can be applied to create general flame retardant fabrics.