PETpla.net Insider 07+08 / 2020

MATERIALS / RECYCLING PETplanet Insider Vol. 21 No. 07+08/20 www.petpla.net 26 Cyanoacrylate UV blocker promises good processing features and long wavelength coverage A new UV blocker for PET PET as a substrate, made in films or containers, provides great transparency, atmosphere bar- rier and mechanical strength for various applications. An addition of UV blocking is necessary everywhere where UV sensitive ingredients such as vitamins, colourants or fragrances have to be protected from degradation. PET films completely covering 400nm or beyond are allowed more potential usage to protect human eyes from frequent usage of 3C devices. Chitec Tech- nology has filed a patent for its first cyanoacrylate UV blocker and launched Chiguard GA403 at K2019, aiming for good processing possibilities and long wavelength coverage. UV is commonly considered a radiation from the sun, and organic UV absorbers are recognised for prolong- ing polymers service life, retaining colour stability, gloss and mechanical strength and so on. Commercially available UV absorbers developed from various com- pounds such as benzophenones, ben- zotriazoles, hydroxyltriazines, cyanoacr- ylates and others are each having its unique absorption ranges and limita- tions. These chemicals are recognised as being highly efficient at absorbing high energy UV light and dissipating it as heat which is then released. Chitec Technology has been heavily involved in organic UV absorber studies for dec- ades, and pushed for long wavelength absorption especially suitable for PET substrates. When it comes to PET, many UV absorbers are not considered suit- able because they cannot meet the required temperature of 230°C or higher. Amongst the choices available, many benzotriazoles, benzophenones are regarded as being unsuitable because of their low decomposition temperature and often cause yellowing. Amongst the most popular UV absorbers used in PET resins are 2-(2H-Benzotriazol-2-yl)-4,6-bis(1- methyl-1-phenylethyl)phenol (CAS no. 70321-86-7) 2-(4,6-diphenyl-1,3,5-triazin- 2-yl)-5-[(hexyl)oxy]-phenol (CAS no. 147315-50-2) or 2,2 ′ -(1,4-Phenylene) bis[4H-3,1-benzoxazin-4-one] (CAS no. 18600-59-4), all of which are able to sustain processing temperatures above 300°C. Of the organic UV absorbers avail- able, many have peak absorptions around 330~350nm but when bottle producers require a 380nm~400nm cut off, very few UV absorbers can be used. Cyanoacrylate chemistry has been selected as industrially approved safe for food packaging usage with supe- rior long wavelength coverage. This is essential to protect nutrition ingredients or retain colourants stability, which are sensitive to UV. Chitec studies have shown that absorbing blue light ranges up to 410nm is also achievable. This unique performance is all the more interesting as we are surrounded in our daily life by mobile 3C devices with large LCD screens. One of the critical breakthroughs of this new compound is the peak absorption at 363nm as shown in Fig. 1. When long wavelength coverage is considered, especially 380nm or above, peak absorp- tion wavelength plays a decisive role in efficiency. From an organic chemis- try perspective, however, attempts to redshift 5 or 10nm from any existing chemicals are not easily achievable. With some dosage options in 1mm thick- ness PET specimen, Chiguard provides com- plete coverage of the UV spectrum from 400nm and below as shown in Fig. 2. To achieve the same performance with other UV absorbers, a much higher dosage is required, which then has the possible side effects of yellowing or blooming. Chiguard has a 10% weight loss at temperatures above beyond 350°C, which is manageable for PET com- pounding process. Thermal stabil- ity of UV additives is recognised as another important factor. Chitec states that Toray’s study (extracted from US20150183957A1) gives a good understanding of the benefits of using UV absorbers during the polymerisa- tion process compared to commercially available UV masterbatch. At a tempera- ture of 280°C maintained for several hours, there is an inevitable loss of UV absorbers when polymerisation is carried Fig. 1 Fig. 2