Influence of Molecular weight of PEG on the mechanical properties of Polyurethane Dispersion

Polyurethane dispersions (PUDs) have considerably become the focus of searching attention among all waterborne resins thanks. In this study, a series of polyurethane dispersions (PUDs) based on castor oil and polyethylene glycol (PEG) with different molecular weight (Mw), 1000, 2000, and 3350 were synthesized. Also, Isophorone diisocyanate (IPDI) and dimethylol propanoic acid (DMPA) were used as hard segment to the synthesis of PUDs by methyl ethyl ketone (MEK) process. The appearance evaluation has shown that PUD becomes more transparent as the molecular weight of PEG increases. The sample PUD-1000 with PEG Mw of 1000 is yellowish. Furthermore, mechanical tests like gloss, hardness, drying time, MEK resistance, and water resistance have been conducted as shown in Table 1. With rising in Mw of PEG, the gloss and hardness decline. Drying time has reached from 6 to 22 minutes as the Mw of PEG goes up. Besides, PEG is a biodegradable material thanks to its hydrophilicity and soft segment content increases compared to hard segment content by raising the Mw of polyol; Therefore, hydrogen bonding density decreases which results in decrease water-resistance of the system as can be seen in Table 1. Also, as the Mw of PEG goes up from 1000 to 3350, the chain length increases by larger Mw of polyol which leads to higher solubility in MEK. As illustrated in Table 1. PUD-1000 has the most suitable mechanical properties in comparison to samples with larger Mw of PEG. Moreover, the DSC results are depicted in Fig. 1 in which PUD-3350 with the largest Mw showed lower glass transition temperature (Tg) due to the less hydrogen bonding density. It is expected this study can be helpful to manufacture PUDs with high quality and properties in the wood industry, coating industry, leather industry, and so on.