Polyurethane dispersions for paper coatings

[摘要] ENGLISH ABSTRACT:Aqueous polyurethane (PU) dispersions were synthesized for the use in paper coatings.These PUs contained a polyester polyol soft segment (content of 60-70%) and a urethanehard segment (content of 30-40%). This was followed by grafting using four different graftingagents. Triethylamine (TEA) was used as the neutralizing agent. The polyester polyolsegment consisted of neopentyl glycol (NPG), adipic acid, 1,4-cyclohexane dicarboxylic acid(1,4-CHOCA) and 2-phosphonobutane-1 ,2,4- tricarboxylic acid (PSTCA), while the urethanehard segment consisted of hydrogenated 4,4-diphenylmethane diisocyanate,dimethylolproponic acid (OMPA), 3-hydroxypivalic acid (HPA) and hydroxyethylenemethacrylate (HEMA). The grafting agents used were lauryl methacrylate (LMA), n-butylmethacrylate (n-SMA), methyl methacrylate (MMA) and styrene.Two different polyester polyols were synthesized, one containing 10% phosphate and theother none. The polyols were characterized in terms of their acid value, hydroxyl value andmolecular mass. The PUs synthesized from the polyol containing 0% phosphate were graftedwith LMA, while the phosphate-containing PUs were grafted with each of the all four graftingagents.The resulting dispersions were applied to paperboard, and then dried at a maximumtemperature of 100°C. The PU-coated paperboard was characterized using the moisturevapour transmission rate (MVTR), and scanning electron microscopy (SEM) techniques.PU films (not supported by paper, stand alone) were prepared by heating the PU dispersionin Teflon holders up to 130°C for 6 hours. The dried films were then characterized bythermogravimatric analysis (TGA), differential scanning calorimetry (OSC), dynamicmechanical analysis (OMA) and Fourier transform infrared spectroscopy (FTIR).MVTR-analysis showed that the phosphated PU coatings had a minimum MVTR-value at 0%grafting, and that its overall MVTR-values were much lower than that of the non-phosphatedPU coatings. SEM-analysis showed that the phosphated PU coatings had no pinholes at amaximum of 8% grafting, while the non-phosphated PU coatings showed pinholes at alllevels of grafting. OMA-analysis showed that the phosphated PU samples had higher Tg's (Tgonset between O-S°C)than that of the non-phosphated PU samples (Tgonset below -SO°C).

[发布机构] Stellenbosch University