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Radiation curing: coatings and composites

Berejka A. J., Montoney D., Cleland M. R., Loiseau L.

Nukleonika

2010

Vol. 55, No. 1

97-106

The initial experiments conducted in the late 1960's at Radiation Dynamics, Inc. (now IBA Industrial, Inc.) showed that by removing the pigment from a radiation curable coating formulation, the same binder system could be used as a matrix system for electron beam (EB) cured fiber reinforced composites. Recently, the binder systems used for EB curable coatings have also been successfully used (without pigments) as the matrices for EB and X-ray cured fiber composites. Insights gained from the development of coatings were translated into desirable properties for matrix materials. For example, understanding the surface wetting characteristics of a coating facilitated the development of a matrix that would wet fibers; the development of coatings that would adhere to rigid substrates as metal while being bent, as for coil coatings, and which would exhibit impact resistance when cured on a metal also imparted impact resistance to cured composite materials. Thermal analyses conducted on the coating binder cured at low energies were consistent with analyses performed on thick cross-sections as used for matrices. The configuration of the final product then dictated the modality of curing, be it low-energy EB for coatings or higher energy EB or X-ray curing for composites. In industrial radiation chemistry, one deals with monomers and oligomers (similar to 102 and similar to 103 to 104 Daltons molecular weight, respectively). Thus, one can approach the development of coating binders or matrix systems as one would approach the synthesis of organic polymers. The desired final material is a fully cured and cross-linked polymer. In contrast, concepts involved in “formulating” are often derived from dealing with high molecular weight polymers (similar to 105 + Daltons) in which intense mechanical mixing is used to bring different ingredients together. When synthesizing a radiation curable coating or matrix system, greater attention is given to microphase compatibility as reflected in the microhomogeneity of the entire material.

Effects of vitrification on the isothermal polymerization of acrylate blends under radiation

Chuda K., Smolinski W., Defoort B., Rudz W., Gawdzik B., Rayss J., Coqueret X.

Polimery

2004

T. 49, nr 7-8

505-513

The radiation-induced polymerization of some acrylate oligomers was investigated by means of FT-IR spectroscopy applied to films of various thickness that were cured under isothermal conditions. Different types of oligomers, one polyethyleneglycol diacrylatc (PEGDA), one polyurethane triacrylate (PURTA), and one epoxy diacrylate derived from bis-phenol A (EPDA) were selected for their contrasting networks properties, with a low, intermediate, and high T(g) of the radiation-cured materials, respectively. In order to gain a deeper insight into the effect of gradual vitrification on the reactivity of the polymerizable systems, the conversion - dose profiles of the epoxy diacrylate were recorded at various temperatures. The dependence of the limiting conversion on the polymerization temperature was examined under various experimental conditions and compared with the conversion - T(g) relation, which was deduced from dynamic thermo-mechanical analysis. The correlation between resulting T(g) measured in the samples at maximal conversion for each curing temperature was shown to be slightly deviating from linearity. A phenomenological model of the reaction kinetics was shown to depict satisfactorily the observed photopolymerization profiles. From the well-determined T(g) - conversion relation, a semi-mechanistic kinetic model taking into account the gradual vitrification of the network can be foreseen.

Metodą FT-IR zbadano przebieg inicjowanej promieniowaniem UV bądź strumieniem elektronów (EB) polimeryzacji diakrylanu glikolu polioksyetylenowego (PEGDA), triakrylanu poliuretanu (PURTA) oraz epoksydiakrylanu pochodnej bisfenolu A (EPDA) [wzory (I)-(III)]. Utwardzone polimery charakteryzowały się, odpowiednio, niską, pośrednią i wysoką wartością temperatury zeszklenia (T(g)). Jako inicjatorów polimeryzacji użyto produktów handlowych o nazwach "Darocur 1173" - wzór (IV) oraz "Irgacure 651" - wzór (V)]. Określono charakter wpływu dawki promieniowania na wydajność (G) polimeryzacji PURTA i EPDA (rys. 4), a także zależność G w polimeryzacji EPDA od temperatury utwardzania, rodzaju inicjatora i czasu (rys. 7, 8, ta-bela 1). Innym analizowanym parametrem była maksymalna wydajność polimeryzacji (G(max)); zbadano wpływ temperatury utwardzania PEGDA i EPDA na G(max) a w przypadku EPDA - dodatkowo wpływ ilości i rodzaju inicjatora oraz grubości próbki (rys. 6,9,10). Temperaturę zeszklenia utwardzonych próbek EPDA oznaczano metodą dynamicznej analizy termomechanicznej (rys. 11). Pozwoliło to na ocenę zależności wartości T(g) od temperatury sieciowania (rys. 12). Zależność ta ma charakter liniowy jedynie do pewnej wartości temperatury polimeryzacji, po przekroczeniu której następuje znaczne odchylenie od liniowości. Stwierdzono, że zaproponowany fenomenologiczny kinetyczny model reakcji izotermicznej polimeryzacji [równanie (6)] dobrze opisuje badany proces. Na podstawie wyznaczonych zależności T(g)-konwersja można przewidzieć semi-mechanistyczny kinetyczny model stopniowego zeszklenia w toku polimeryzacji.