Facile synthesis and characterization of novel multi-functional bio-based acrylate prepolymers derived from tung oil and its application in UV-curable coatings

With the growing depletion of fossil energy and the unceasing joint efforts to maintain sustainable development, bio-based materials are appealing for academic and industrial researchers because they possess the merits of environmental friendliness and renewability. In this study, a tung-oil-based derivative, tung-maleic anhydride (TMA), which was prepared from methyl eleostearate and maleic anhydride, reacted with epichlorohydrin to synthesize epoxidized tung-maleic anhydride (ETMA) after the hydrolysis of anhydride. Furthermore, ETMA was chemically modified by pentaerythritol triacrylate to obtain hexa-functional epoxidized tung-maleic anhydride acrylate prepolymers (PETMA). The chemical structure of the resultant prepolymers was confirmed by FT-IR and ¹H NMR, while the rheological behavior of prepolymers was investigated by using a rheometer. Also, the curing efficiency of different photoinitiators on PETMA prepolymers was investigated, and the result revealed that the tung oil-based prepolymers could be rapidly cured with 3.0 wt% photoinitiator PI-819 under a UV lamp with 5 kW light intensity within 45 s. Furthermore, various reactive diluents were used to be cured with PETMA prepolymers, and the thermomechanical properties, mechanical properties, volume shrinkage, swelling property, and general performances of the resultant UV-cured films were investigated. DMA results revealed that, among the films cured by the reactive diluents with same functionality, reactive diluents with a higher T_g resulted in a higher T_g toward the resultant cured films. The crosslinking density (ν_e) of the films cured with various reactive diluents was determined by the double bond density, leading to the fact that the films cured with bi-functional reactive diluents exhibited a higher crosslinking density than the ones cured with mono-functional reactive diluents. TGA results showed that high crosslinking density facilitated improving the thermal stability of the cured films, while the steric structure in film matrix exerted adverse effect on thermal stability. Besides, tensile test indicated that high crosslinking density and steric structure facilitated the enhancement of mechanical properties toward the resultant films. More strikingly, all UV-cured films possessed excellent hardness, high glossiness and remarkable water resistance, and these high-performance bio-based UV-curable films are promising for widespread applications.