ABSTRACT
Polyurethanes (PU), which are available in two packs (2K) and one pack (1K), are extensively used in protective coatings due to its excellent properties like scratch resistance, impact hardness and weather resistance. Polyurethane coatings however, suffer from disadvantages such as, inferior thermal stability and abrasion resistance which can be overcome by using inorganic additives in the form of nanomaterials [1-6]. Corcione et al. [7] have studied the rheological properties of PU adhesive system containing of nanoclay improved the rheological and mechanical properties by intercalation and exfoliation mechanism. Somani et al. [8] have prepared the high solid PU coatings using castor oil based polyester polyol resin. Generally, the technique of simultaneous addition of the inorganic particles during the polymerization is not used [9] as it has been observed that the nano-size inorganic particles have a strong tendency for agglomeration because of their high surface energy [10]. The reduction in surface energy can be achieved by surface modification of inorganic particle with an organic molecule. Some studies demonstrated the use of surface modified nano-CaCO3[11], nanoclays [6, 7], and nanosilica for improvement in micro hardness, tensile strength, and abrasion resistance of the final film due to fine dispersion of surface modified inorganic nanoparticles in the polymer matrix. It is also reported that the use of nanosilica shows improved scratch resistance [11] in acrylic polyurethane and nano-ZnO imparts UV resistance to the matrix. Furthermore, it was also found that the use of small quantity of (2-5%) nano-CaCO3 shows improvement in hiding power and limits the use of TiO2 in the polymer coatings [12]. The aliphatic 2K PU finishes are used for exterior purpose due to superior UV stability. Plastic components like acrylonitrile butadiene styrene (ABS), poly propylene (PP), poly vinyl chloride (PVC), polyethylene (PE), fiber reinforced plastic (FRP) which are coated with 2K PU (top coat) have been commonly used in the automobile industry. Due to nucleation and isothermal crystallization mechanism, nanoparticles aredispersed in to the composite material which enhances performance of nanocomposite coatings. In the present study, synthesis of saturated polyester polyol was carried out. Phthalic anhydride, adipic acids were used along with neopentyl glycol (NPG) and trimethylol propane (TMP) as the saturated acid and alcohol respectively. Functionalized nanocalcium carbonate and nanobentonite clay particles were incorporated (1-5 wt. %) separately as well as in combination (4 wt. %) in to polyester polyol nanocomposite by in situ polymerization technique and subsequently 2K PU coating was prepared. The mechanical and barrier properties of 2K PU nanocomposite films on ABS substrate were evaluated as per ASTM standards.
