Authors:C. Ruiz, L. Machado, J. Vanin, and J. Volponi
Radiation-curable coatings have acquired importance, because they are environmentally-friendly (no solvent emission)and require
low energy for curing, when compared to other conventional heat-curable products. UV-curable coatings performance depends
on the cure quality. Suitable methods were evaluated to estimate the degree of cure applying quantitative techniques, such
as differential scanning calorimetry (DSC) and differential photocalorimetry (DPC), in order to determine the residual heat
of curing in UV-cured films. The results of the DPC technique showed better sensibility than DSC technique, although the use
of suitable pans for the case of clear coats must be considered.
In the photomicrocalorimetric module designed by Johansson and Wadsö for a commercial Thermometric TAM heat conduction batch
microcalorimeter, the incident light from an external xenon lamp was divided by a beam splitter and directed to the two vessels
of the differential system by light guides ideally to give zero heat flow. In practice this proved difficult and so to improve
the balance between the vessels in terms of the incident light heat output as well as potentially to give more versatility
regarding the choice of wavelengths, the xenon lamp-based system was replaced in the first stage by a pair of cold white LEDs
embedded directly in the test and reference vessels. The LEDs had independent electrical circuits to achieve the balance by
manual adjustment. As a second stage, the test vessel was equipped with PTFE tubing for changing the liquid phase in it while
it was in the middle thermal equilibrium position. This improved the reproducibility of the results.
Authors:Y.-M. Kim, L. Kostanski, J. MacGregor, and A. Hamielec
Both epoxides and vinyl ethers can be polymerized cationically albeit through different intermediates. However, in the case
of epoxide-vinyl ether mixtures the exact mechanism of cationically initiated polymerization is unclear. Thus, although vinyl
ethers can be used as reactive diluents for epoxides it is uncertain how they would affect their reactivity. Cationic photocuring
of diepoxides has many industrial applications. Better understanding of the photopolymerization of epoxy-vinyl ether mixtures
can lead to new applications of cationically photocured systems. In this work, photo-DSC and real-time Fourier Transform Infrared
Spectroscopy (RT-FTIR) were used to study cationic photopolymerization of diepoxides and vinyl ethers. In the case of mixtures
of aromatic epoxides with tri(ethylene glycol) divinyl ether, TEGDVE, photo-DSC measurements revealed a greatly reduced reactivity
in comparison to the homopolymerizations and suggested the lack of copolymerization between aromatic epoxides and TEGDVE.
On the other hand, for mixtures of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, ECH, with TEGDVE the results
indicated high reactivity of the blends. The polymerization mechanism might include copolymerization. To examine this mechanism,
mixtures of the ECH with a tri(ethylene glycol) mono-vinyl ether, TEGMVE, were studied by both photo-DSC and RT-FTIR. Principal
component analysis (PCA) proved to be an efficient tool in analyzing a large matrix of the spectral data from the polymerization
system. PCA was able to provide insight into the reasons for the differences among replicated experiments with the same composition
ratio and supported the hypothesis of copolymerization in the ECH/TEGMVE system. Thus, blends of cycloaliphatic epoxides and
vinyl ethers seem to have a great potential for applications in high-productivity industrial photopolymerization processes.
Authors:G. D. Ye, H. Zhou, J. W. Yang, Z. H. Zeng, and Y. L. Chen
Photoinitiating behaviors of oligo(α-aminoketones) (OAK) macrophotoinitiator
containing aminoalkylphenone group on free-radical photopolymerization had
been investigated by differential photo-calorimetry (DPC). The macrophotoinitiator
showed comparative performance with those commercial photoinitiators with
lower molecular mass. The effect of photoinitiator concentrations and UV intensity
on the polymerization rate was investigated, and the value of exponential
factor was found to be 0.5 at the beginning of polymerization, suggesting
that the photopolymerization initiated by OAK followed biradical termination
mechanism. Photosensitizer isopropyl thioxanthone (ITX) and oxygen severely
restricted the polymerization in these systems. Photoinitiators with lower
molecular mass showed higher reactivity than those with higher molecular mass.
Authors:C. Bentivoglio Ruiz, L. Machado, J. Volponi, and E. Segura Pino
Radiation curing is an environmentally-friendly technology. Furthermore, radiation curing is a faster, energy saving and more
efficient industrial process than the heat-curable process. One of the most important requirements for the widespread application
of UV curable coatings in the coating industry is that they are stable vs. atmospheric degradation. Today's state of the art
in oxidative drying and thermosetting coatings is the use of light stabilizers to protect polymers vs. the damage of outdoor
exposure. Oxygen has a detrimental effect on the cure response of free radical systems, especially in thin-film coatings.
Differential photocalorimetry (photo-DSC) was used to investigate the oxygen effect and the use of light stabilizers on UV
curing of photocurable formulations based on acrylate materials. Coating thickness influence was also considered.