Dissolution And Hydrolysis Recycling Of Waste Polyamide 6 Textiles

With the increase in the number of discarded textiles every year and the improvement of people’s awareness of environmental protection,the recycling technology of textiles has gradually attracted people’s attention.The amount of polyamide 6 in synthetic fibers is second only to polyester,and the annual consumption is large,so it is of great significance to efficiently recycle its waste textiles.At present,the main methods of recycling polyamide 6 include energy recycling,physical recycling,and chemical recycling.Among them,energy recycling will release a large amount of harmful gases while providing thermal energy,which has been phased out;physical recycling is still dominated by melt recycling,but the preparation of the quality of the recycled products varies;the liquid acid catalyst used in the acid hydrolysis method in chemical recycling is difficult to recover,and it is not easy to separate from the product after the hydrolysis.Therefore,more efficient physical and chemical recycling methods have attracted the attention of researchers.Microspheres are high-value products.Thermally induced phase separation can be used to prepare microspheres by physical dissolution.Microspheres are widely used in adsorption,3D printing,coatings and other fields.In chemical recycling,solid heterogeneous catalyst not only has good catalytic effect,but also is easy to separate from the product.Therefore,this subject adopts thermally induced phase separation technology to physically recover polyamide 6,and uses solid acid-catalyzed hydrolysis to chemically recover polyamide 6.The main contents are as follows:The interaction between polyamide 6 with good solvent and poor solvent was explained by Hansen solubility parameter,and it was found that anhydrous formic acid can be used as a good solvent for polyamide 6,and its dispersion force and hydrogen bonding force are the main factors affecting the dissolution of聚酰胺6.Anhydrous formic acid and water were mixed to prepare a mixed solvent with mass ratios of 59/41,58/42,56/44,54/46,and polyamide 6 was dissolved at 90℃.It was found that water would form hydrogen bonds with anhydrous formic acid and reduce the dissolving ability of anhydrous formic acid enables the binary solvent system to dissolve polyamide 6 at high temperature and precipitate polyamide 6 at low temperature,which meets the requirements of thermally induced phase separation method for diluent.To explore the structural transformation of polyamide 6 in the process of dissolving the mixed solvent binary solvent with mass ratio of 56/44 and54/46,the amorphous region of polyamide 6 dissolves first through fiber expansion-chain unwinding,while the crystalline region will dissolve first.It undergoes the process of decrystallization-fiber swelling-chain disentanglement,and finally dissolves completely.In thermally induced phase separation,the polymer solution is pulled into the metastable region in liquid-liquid separation by quenching,which can disperse the polymer-rich phase in the polymer-poor phase and crystallize and solidify into microspheres.Dissolving polyamide 6 in anhydrous formic acid,and after completely dissolving,an anhydrous formic acid/polyamide 6 solution with a mass fraction of 1to 7 wt%is obtained,and add water equivalent to 65～80%of the polymer solution mass after complete dissolution.After dissolving at 90°C for 2 h,low temperature quenching was performed between 10 and 20°C to obtain microspheres.The results show that the mass fraction of 5～7 wt%can form microspheres,the average particle size of the microspheres is in the range of 20～40μm,and the specific surface area can reach 4 times that of the original textile,but the crystallinity tends to decrease with the use of waste polyamide 6 textiles.The original textile is reduced,and it has excellent adsorption performance for acid dyes,and the adsorption model belongs to the Freundlich model.Furthermore,Zr O₂was prepared and composited with SBA-15 molecular sieve with high specific surface area,and then it became a solid acid with super acidic center by impregnation with H₂SO₄and（NH₄）₂S₂O₈.The hydrolysis reaction of polyamide 6 textiles and water was carried out according to the mass ratio of 1:30,and the influence of different types of catalysts on the hydrolysis results was observed.The optimal conditions for solid acid SZ-1-catalyzed hydrolysis of polyamide 6textiles were 0.5 g of SZ-1 catalyst,260℃and 1 h of reaction time,at which time the hydrolysis rate of polyamide 6 and the yield of CPL were 88%and 56%,respectively.the results show that the yield of monomeric caprolactam and polyamide 6 textiles increases with the increase of hydrolysis time and temperature,and the catalytic activity of solid acid was close to that of liquid H₂SO₄,and it has better hydrolysis effect for different types of polyamide 6 textiles.The catalytic mechanism is that it can release H⁺in the process of hydrolysis of polyamide 6 into oligomers to accelerate the formation of oligomers.Further,the oligomer is further hydrolyzed intoε-caprolactam,and the solid acid has a certain catalytic effect after being recycled for four times.