| PU synthetic leather can be used as a substitute for natural leather. But, organic solvent pollution problem would occur in manufacture of polyurethane leather, because the polyurethane used to produce for synthetic leather is based on organic solvent. Therefore, a kind of environment-friendly polyurethane and cleaner production technology should be developed to solve the inconsistency of people’s physical demands and environmental pollution. Using the WPU as the raw material of synthetic leather can solve the pollution problem for PU synthetic leather development. But it exists big gap between waterborne and solvent-based PU, and there are a lot of problems in the manufacture process of waterborne PU leather. So it needs more research in this field.The aim of this study is to solve the organic pollution problem in synthetic leather industry. This study did much valuable work for solving these problems through materials, craft aspects.First, in this study WPU was modified with hyperbranched macromolecules poly-amido amine (PAMAM), and the influence of different generation PAMAM on WPU were studied. The molecular structure of products was characterized by using FT-IR, XRD, TEM, AFM, laser particle size analysis and so on. The results showed that the WPU can be modified by PAMAM after dispersing. The hyperbranched macromolecules PAMAM can be introduced into the PU molecular chain. Intra-molecular crosslinking will appear in WPU modified by low molecular weight PAMAM, and it can reduce the crystallinity of WPU. And high molecular weight PAMAM cannot enter into the colloidal particles, so the crystallinity of the product improved. PAMAM can influence the particle size of the WPU emulsion. PAMAM with low branching degree had little influence on the particle size. With the branching degree of PAMAM rising, the core-shell structure particle formed firstly, and then agglomeration between particles occurred. Finally, certain associative WPU emulsion formed. The viscosity of WPU-HBP from 302 mPa-s add to 612 mPa-s. With the branching degree adding of PAMAM, more crosslinking structure was formed in WPU molecular chain, which affected the accumulation of soft and hard segment and the formation of crystalline domains was also limited. With the branching degree of PAMAM rising, the AFM image of WPU-HBP film became smoother, and the film showed a smoother surface. The physicochemical properties of the film test results indicated that, under a certain amount, PAMAM(G1～G3) with lower branching degree has little effect on mechanical properties, the tensile strength are 28.12Mpa、29.02 Mpa、29.37 Mpa, colse to 28.03Mpa(WPU-blank). However, modified by PAMAM (G4、G5)with higher branching degree, the tensile strength is reduced to 27.53Mpa(WPU-G4)and 24.84Mpa(WPU-G5). In addition, PAMAM with low branching degree can improve heat-resisting performance of film obviously, and heat-deformation temperatures increased from 173.5℃ to 192.1 ℃. Then, with the branching degree of PAMAM rising, heat-deformation temperatures decreased gradually from the 192.1℃ to 177.5 ℃, indicated that PAMAM with higher branching degree has limited impact on its heat-resisting performance. The text results showed that WPU film modified by PAMAM has good water resistance, and water absorption decreased from 10.47% to 4.64%. Moreover, PAMAM can reduce the surface energy of film, so the WPU-HBP have larger water contact angle than the WPU-blank(76.5°). The largest is 86.6°(WPU-G2) and the sarmller is 79.2°(WPU-G5)Secondly, in order to meet the demands of high solid content of the aqueous polyurethane in WPU synthetic leather processing, a series of sulfonic-carboxylic acid waterborne polyurethane were prepared. Meanwhile, the high solid PU was modified with PAMAM to improve its properties. The effect on the properties of WPU structure of sulfonic acid and carboxylic acid hydrophilic group was studied. The emulsions are characterized by using FT-IR, XRD,TEM, AFM, laser particle size, Zeta potential analysis and so on. The particle size distribution of emulsion became wider with the sulfonic group content addtion. It was conducive to the formation of high solid content polyurethane. The results showed that latex solid content increased significantly by increasing the sulfonic group content., the highest percent of solid content is 50.25%(ZW4) by experimential preparation, it has obviously been raised than ZW1(37.72%). The the degree of soft and hard segments aggregate alone becomes strong with the sulfonic acid group content increasing. The Zeta potential analysis results showed that the pH stability of waterborne polyurethane emulsion containing sulfonic acid groups was improved significantly than waterborne polyurethane containing carboxylic acid type. The pH stability was greater with the sulfonic acid group content increasing, from pH5.5 improve to pH3.8. The Zeta potential of emulsion was gradually increased with the increase of sulfonic group content from -42.5mVimprove to -62.7mV. This showed that the stability of the emulsion was better. The results of physical and mechanical properties showed that the tensile strength of the film gradually reduced and elongation increased with the of sulfonic acid group content increasing, but with the PAMAM modified, the tensile strength of the sample is 18.12Mpa, heat resistance is 169.5℃, water absorption is 9.45%, it was improve than the samples without PAMAM modified.Then, in order to improve the initial adhesion and adhesive fastness of WPU, the water-soluble polyester polyol containing anionic sulfonic group was brought into the molecular chain of WPU, due to the high stability of sulfonic group in different pH circumstances, then the amphoteric ionic polyurethane was obtained. The emulsions are characterized by using FT-IR, XRD, TEM, AFM, laser particle size, Zeta potential analysis and so on. The results showed that the sulfonic acid group was formed by following the expected reaction route. The amphoteric polyurethane can form stable emulsion in either acidic or alkaline circumstances. The latex particles were of nice round shape, unhomogeneous and small. The film presented the special state of film forming. It was easy to form a heterogeneous membrane. It was because the waterborne polyurethane contained both anion groups and cation groups. Due to the phase change, interface makes waterborne polyurethane hydrophilic group distributed changes occur, so that the ionization equilibrium of aqueous polyurethane particles are detroied, thus creating more obvious heterogeneous film state. The potential analysis for emulsion indicated that the amphoteric ionic polyurethane emulsion has high stability in different pH solution, and can exist steadily in pH value between 4.6 ～8.5 ranges. The Zeta potential of the emulsion was 50.4mV under acidic conditions, and it was showed cationic. The Zeta potential of the emulsion was-48.3mV in alkaline conditions, and it was showed anion. It is good to use as adhesive in waterborne PU leather manufacture.Finally, the study key point is to produce the waterborne PU synthitce leather. The study explored the waterborne polyurethane synthetic leather engineering technology program. That used the WPU-G2 as surface layer, the BWPU as adhesive layer, the ZW5 as foam layer. The WPU synthetic leather was prepared through technology improvement innovation and formulation adjustment optimization. The structure and properties of the waterborne PU synthetic leather were analyzed. The results showed that the peel strength is 31.5N, abrasion resistance≥1000, folding fastness≥50000 times, anti-adhesion 4-level, and the permeability is 710mL/cm2·h. These properties have reached the solvent-based leather physical standard. The moisture permeability is 948g/m2·24h, better than solvent PU leather. After the comprehensive comparison, it could find that the preparation technology of waterborne PU synthtice leather is feasible. It is valuable that use the waterborne PU wet process and dry process technology to prepare synthetic leather. |
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