Surface preparation polyurethanes

Polymer Surface Preparation and Characterization. Three polyurethane ureas were prepared as previously described (12). 

Both, aniline and anilium hydrochloride were polymerized in direct and in inverse miniemulsion, respectively [140]. The polymerization of anilium hydrochloride, which was initiated by hydrogen peroxide, yielded a highly crystaUine emeraldine polyaniline. In direct miniemulsions, additional stabilizers (e.g., poly(vinyl pyrroU-done) or PVA) were employed to preserve colloidal stability. The polymerization of aniline in direct miniemulsion has also been reported [141] in this case, following polymerization the polymer was first treated with stannous chloride and then doped with p-toluenesulfonic acid. A dramatic increase in conductivity after treatment with stannous chloride was considered due to pernigraniline moiety in the emeraldine base structure having been reduced. Such oxidative polymerization of aniline may be used to add an additional conductive shell to preformed latexes. For example, Li et al. polymerized aniline in the presence of dodecylbenzesulfonic acid on the surface of polyurethane and polyurethane/poly(methyl methacrylate) nanoparticles prepared in miniemulsion [142]. 

In Volume 1, we have provided general information about adhesives and sealants with the chapters Technical Characteristics of Adhesives and Sealants , Surface Preparation before Bonding and Polyurethane Adhesives and Sealants . 

Nano-anulsions constitute an attractive alternative for preparing polyurethane nanoparticles because of their small droplet size and, consequently, very large surface area and high kinetic stabiUty. - Nano-emulsions are a class of emulsions with a uniform and extremely small droplet size, usually ranging between 20 and 200 nm. They can be classified as oil-in-water (OAV) or water-in-oil (W/O) nano-emulsions if the internal phase is constituted by oil or aqueous droplets dispersed in aqueous or oily external phase, respectively. Therefore both hydrophobic and hydrophilic... 

The poly(MPC) brush gave a quite wettable surface. The contact angle of the water droplet (2.0 pL) on poly(MPC) brush surface was very low (below 5°). The contact angles of methylene iodide and hexadecane were 45° and <5°, respectively. Using the Owens-Wendt equation [49], the surface free energy of the poly(MPC) brush surface was estimated to be 73 mJ/m, which is quite similar to that of water. Therefore, water plays the role of a good solvent, resulting in low friction of the poly(MPC) brush. Ho et al. [50] prepared a low-friction surface on polyurethane... 

The heparin Immobilized polyurethane surfaces (prepared by plasma grafting of 1 acryloyl benzotrlazole and subsequent hydrolysis/amlnatlon) are effective In suppressing thrombus formation. The adhesion of peripheral blood mononuclear cells was also lower on such modified surfaces [72]. Heparin immobilized on vinyl pyridine grafted styrene butadiene-styrene block copolymers also shows good biocompatiblllty. The adsorption of albumin and fibrinogen are reduced with the increasing graft levels and heparin content [41]. 

Abstract This chapter constitutes one of the very few reviews in the existing literature on shoe bonding, and it gives an updated overview of the upper to sole bonding by means of adhesives. The surface preparation of rubber soles and both the formulations of polyurethane and polychloroprene adhesives are described in more detail. The preparation of adhesive joints and adhesion tests are also revised. Finally, the most recent development and technology in shoe bonding is described. 

Depending on fashion, each year different materials have been and are currently used in the manufacturing of shoes, ranging from rubber soles (vulcanized styrene-butadiene rubber (SBR), thermoplastic rubber, EPDM) to different polymers (leather, polyurethanes, ethylene-vinyl acetate (EVA) copolymers, polyvinyl chloride (PVC), polyethylene, Phylon). To produce adequate adhesive joints, surface preparation of those materials is required (see part B Surface treatments). Surface preparation procedures for these materials must be quickly developed and the validity of these treatments is generally too short. Several procedures have been established to optimize the upper to sole bonding, most of them are based in the use of organic solvents. Due to environmental and health issues, solvents should be removed from the surface preparation procedure and several environmental friendly procedures for the surface preparation of several materials have been proposed. 

Most of the upper and sole materials used in shoe industry cannot be directly joined by using the current adhesives (polyurethane and polychloroprene adhesives) due to their intrinsic low surface energy, the presence of contaminants, and antiadherend moieties on the surface. Therefore, the surface preparation of upper and sole must remove contaminants and weak boundary layers, and roughness and chemical functionalities able to produce adequate bond strength should be created. 

Styrene-butadiene-styrene (SBS) block copolymers are adequate raw materials to produce thermoplastic rubber (TR) soles. SBS contains butadiene domains — soft and elastic and styrene domains - hard and tough. Because the styrene domains act as cross-linking agents in the SBS structure, vulcanization is not necessary to provide dimensional stability. TR rubber soles generally contain polystyrene (to impart hardness), plasticizers, fillers, and antioxidants processing oils can also be added. TR rubber soles have a low surface energy, so to reach proper adhesion to polyurethane adhesive a surface modification is needed. Special adhesives have been developed to avoid surface preparation but they have poor creep resistance. 

The application of surface treatments to SBR rubber soles should produce improved wettability, creation of polar moieties able to react with the polyurethane adhesive, cracks, and heterogeneities should be formed to facilitate the mechanical interlocking with the adhesive, and an efficient removal of antiadherend moieties (zinc stearate, paraffin wax, processing oils) have to be reached. Several types of surface preparation involving solvent wiping, mechanical and chemical treatments, and primers have been proposed to improve the adhesion of vulcanized SBR rubber soles. Chlorination with solutions of trichloroisocyanuric acid (TCI) in different solvents is by far the most common surface preparation for SBR rubbers. 

In the past, polychloroprene adhesives were more extensively used in upper to sole bonding, but nowadays polyurethane adhesives are preferred. Polychloroprene adhesives have better tack and improved wettability than polyurethane adhesives, but the polychloroprene adhesives are not compatible with surface chlorinated rubber soles and cannot be used to joint PVC soles. Therefore, polyurethane adhesives show better versatility on higher number of substrates and also have lower oxidative degradation in time. However, they require always the surface preparation of the materials to be bonded. 

---