| Polyamide/cotton fabrics have excellent wearability, exceptional friction-resistance and good dimensional stability, so that they are widely used as work clothes, casual clothes, uniforms, underwear and outdoor products, et al. As a consequence, environmental pollution and resource wasting are introduced by used and wasted polyamide/cotton fabrics. It is an important manner to maximize the recycling and reuse of waste textile products for a cyclic economic development.As a result of the great difference between the performance and recycling methods of polyamide and cotton fibers, the key technology for recycling of waste polyamide/cotton fabrics is to sufficiently and efficiently separate the polyamide and cotton fibers before the recycling process of each component. Two imidazole ionic liquids, 1-allyl-3-methylimidazolium chloride([AMIM]Cl) and 1-butyl-3-methylimidazolium chloride([BMIM]Cl) were used to effectively separate the polyamide component and the cotton component in waste polyamide/cotton fabrics by the selective dissolution mechanism. The freeze-drying method was used to prepare regenerated cellulose porous composite materials. The added chitosan powders improved the anti-microbial property and mechanical performance of the porous composite. In addition, melt blending and in-situ polymerization were used for the preparation of polyamide self-reinforcing composite materials, which provided technical routes for the sufficient and effective reuse of polyamide and cotton fibers after their separation.Cotton fibers were dissovled by [AMIM]Cl and [BMIM]Cl. The dissolution process of cotton fibers in both liquids were studied, including the solubility in different conditions, as well as characterization of structures and the properties of regenerated cellulose films. At 120 °C, the solubility of cotton cellulose in [AMIM]Cl and [BMIM]Cl were 14.6% and 10.2%, which showed both are good solvents. The solubility of cotton fabrics raised with the temperature. The dissolving time increased with increasing fabric content and decreased with raising temperature. Type I cellulose crystal transformed into type II cellolose crystal after regeneration of the cotton cellulose in the ionic liquids. As the dissolution temperature increased from 80 °C to 110 °C, the degrees of polymerization regenreated from [AMIM]Cl and [BMIM]Cl dropped by 9.9% and 7.3%, respectively. As the dissolving time increased from 1 h to 3 h, the degree of polymerization regenreated from [AMIM]Cl and [BMIM]Cl dropped by 27.6% and 33.8%, respectively, with decreased crystallinity and thermal stability of the regenerated cellulose films. When the cotton fiber content was 4 wt% the strength and elongation at break reached their maximum values at 38.8 MPa and 6.8%, which showed good mechanical properties of regenerated cellulose films by the ionic liquid dissolution method.Base on the study of dissolution properties of cotton fibers by the ionic liquid method, waste polyamide/cotton fabrics were separated by [AMIM]Cl and [BMIM]Cl solutions. At same isolation conditions, morphological evolutions of cotton fibers and polyamide fibers were observed in the ionic liquid. The influence of dissolution temperature, dissolving time, and solid/liquid ratio on separation ratios were studied. The surface morphological features, chemical structures, thermal stability and crystallization property of polyamide/cotton fabrics were compared before and after the separation. The isolation mechanism of polyamide/cotton fabrics were analyzed by the ionic liquid solution method. 3 wt% waste fabric were dissolved in [AMIM]Cl at 110 °C under continuous mechanical stiring for 80 mins, and the recycling ratios of regenerated cellulose and polyamide fibers were 54.5% and 42.5%, respectively; 3 w% waste fabric were dissolved in [BMIM]Cl at 110 °C under continuous mechanical stiring for 120 mins, and the recycling ratios of regenerated cellulose and polyamide fibers were 54.6% and 41.5%, respectively. After [AMIM]Cl dissolution isolation, traces of residual cellulose films were found on the surface of polyamide fibers without noticeable change on the surface microstructure of polyamide fibers. During the dissolution and separation process, the cotton cellulose macromolecular segments were broken and directly dissolved in the ionic liquid without derivative reaction. However, the thermal stability and crystallization property decreased. Meanwhile, since the polyamide fibers were insoluble in [AMIM]Cl, good morphology maintained and the chemical structure, the thermal stability and the crystallization property unchanged. The selective dissolution method is effective in the separation of polyamide/cotton fabrics.Base on the study of dissolution separation of waste polyamide/cotton fabrics, further characterizations were carried out on the preprations and properties of Chitosan/cellulose porous composite materials. Chitosan microparticles were added as the reinforcing agent to enhance the composite’s antimicrobial and mechanical properties. Influences of chitosan microparticles content on the microstructure, anti-microbial property and swelling kinetic of the regenerated cellulose composite were investigated. Changes in crystallization property and thermal stability of the cellulose porous composites before and after chitosan incorporation were analyzed. The surface of the chitosan/cellulose porous composites is smooth and in a purely white color. It is in a flannel shape with great hand feeling. The porous composites show three-dimensional interconnected micro pores with a size distribution between 100-150 μm. When the foaming agent content was 300 wt%, cellulose content was 3 wt% and chitosan content was 1 wt%, the pore ratio of regenerated composite sponge was 72.7%, and MVTR after 24 h was 87.8 g/m2 h. The moisture absorption ratio and the relative water retention were 28.03 g/g and 17.36 g/g, then the strength and elongation at break were 0.32 MPa and 25.39%, respectively, and the sizes of inhibition zones against S. aureus and E. coli were 8.5 mm and 6 mm, with inhibition ratios of 95.68% and 98.89%, respectively. The hydrogen bonding was formed between the carboxylic groups of chitosan and the functional groups of cellulose molecules, and the hydrogen bonding between the-NH- group of chitosan and the hydroxyl group of cellulose was formed. Thus, the intermlecular forces existed between chitosan and cellulose molecules. Intermolecular hydrogen bonding between the cellulose molecules were partially broken by the addition of chitosan powder, so that the crystallization properties of regenerated cellulose porous composites were changed, meanwhile the thermal stabilities were also enhanced.Polyamide composites with recycled polyamide 6 fabrics were prepared through both melt blending and in-situ polymerization. The surface features, chemical structures, crystallization properties, thermal stabilities and tensile properties of polyamide self-reinforcing composites from the two recycling and reuse methods were characterized. The mechanism of tensile fracture was analyzed by observing the morpholoy of the fracture surface. After melt blending, a homogeneous material was obtained from waste fabrics with unchanged chemical structure of polyamide. The complex viscosity decreased with an increasing shear rate, which demonstrated the non-Newtonian shear thinning effect and pseudo-plastic rheological characteristics. Both the storage modulus and loss modulus were higher than that of the materials from pure polyamide 6 fabrics, which could be resulted from the inclusion of spandex residuals. The melting point and crystallization point were 225 °C and 187° C, respectively. A notable small absorption peak below the melting point was attributed to the solid-solid transition between different polyamide crystalline structures. Compared to the material obtained from waste polyamide 6/ spandex fabrics, the breaking strength and elongation were 46.6 MPa and 0.04 mm/mm, which indicated the spandex component harmed the recycling and reuse of waste polyamide fabrics. The breaking elongation of polyamide self-reinforcing composites from 60 wt% waste polyamide fabrics and 40 wt% virgin polyamide pellets was significantly increased to 2.0 mm/mm.No distinctive interfacial separation was observed at the fracture section of the polyamide self-reinforcing composite via in-situ polymerization, which indicated good adhesion between the fiber and the matrix. The fracture mechanism was fiber fracture. The absorption peak at 3400 cm-1 resulted from the-OH stretching vibration of hydrogen bonding formed between the polyamide 6 matrix and polyamide 6 fibers, which was an indication of good compatibility at the fiber/matrix interface of the self-reinforcing material. In the small angle X-ray diffraction spectrum, the diffraction intensity for the composite was lower than pure polyamide 6. Meanwhile, lower degree of orientation was displayed. These originated from the formation of a continuous fiber/matrix interfacial structure at 170 °C, due to partial melting of the polyamide 6 fiber surface. The peak at 212 °C corresponded to the melting temperature of α-crystal, while the crystallization temperature was 169 °C. Both the melting and crystallization processes did not show peak splitting, which demonstrated complete compatibility between PA6 fibers and the in-situ polymerized PA6 matrix. The conversion rates of caprolactam in pure polyamide 6 and self-reinforcing polyamide 6 composite were 94% and 80%, respectively. Water residue on the polyamide 6 fiber surface acted as the inhibition of the anionic polymerization of caprolactam. When the polyamide fiber content was 20 wt%, comparing with neat polyamide the impact strength, fracture strength and elongation of polyamide composites were increased by 117%,150% and 10.5%, respectively, which indicated that polyamide 6 fibers had a good reinforced effect for the polyamide 6 matrix. |
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