ADDITIVES | PVC
According to a recent in-vitro metabolism study
on DOTE, it has been shown with the use of 119
SnNMR spectroscopy that read-across from
DOTC to DOTE is not justifiable, Frenkel said. As a result of the recently completed studies (including both in-vitro metabolism and prenatal develop- ment toxicity studies), it was convincingly demon- strated that DOTE is not a Category 1B reprotoxi- cant; Europe is now the only region where it is classified as such.
Figure 1: Comparison of Mark 17 MOK (High DOTE-containing stabiliser) with Mark 21 MOK-A (High MOTE-containing stabliser). Formulations stabilised with Mark 21 MOK-A exhibit more rapid gelation and higher fusion torque, particularly with PVC resins containing copolymer (rheology adjusted to maintain same process parameters by reducing loadings of HMW process aids and/or increasing the external/internal lubricant ratio). Source: Galata Chemicals
April, Galata’s Vice President of Technology, Dr Peter Frenkel, said prospects for octyltin stabilisers are now gaining momentum in Europe. The use by the European Chemicals Agency
(ECHA) of the “read-across” approach for classify- ing products has, until recently, clouded the horizon for octyltin stabilisers. Read-across is one of a number of procedures that use similarities between chemicals within a chemical category to enable data gap-filling. A chemical category is a group of chemicals whose physicochemical and human health and/or ecotoxicological properties and/or environmental fate properties are consid- ered likely to be similar or to follow a regular pattern. Read-across is used to predict end-point information for one chemical by using data from the same end-point for another chemical consid- ered to be similar in some way. “As a result of limitations in analytical methods historically it was incorrectly determined that organotin thioglycolate substances hydrolyse to corresponding alkyltin chlorides,” Frenkel said. “This determination allowed for read-across [from dialkyltin chlorides] to close data gaps as part of the REACH registration process for the sulphur- containing alkyltin esters such as di-octyltin bis(2-ethylhexyl mercaptoacetate) [DOTE].”
84 COMPOUNDING WORLD | June 2018
Harmonised classification Taking into the consideration the new data in February 2016, the German Competent Authority for REACH (BauA) submitted a proposal for a new harmonised classification of DOTE as a Category 2 reprotoxicant. “This is the first step in reclassifying and getting DOTE removed from the SVHC list in Europe,” Frenkel said. It is expected that the Commit- tee for Risk Assessment will adopt an opinion on the proposed classification in the near future. While this has been going on, Galata has developed Mark 21 MOK-A, a new stabiliser with high MOTE (mono-octyltin tris(2-ethylhexyl mercaptoacetate) content. Mark 21 MOK-A addresses the current regulatory status of DOTE, Frenkel said. “Heat stabilising and rheological performance of Mark 21 MOK-A in the most critical applications matched performance requirements of the conventional Mark 17 MOK, a high DOTE- containing stabiliser,” he said (Figure 1). “Reclassification should remove all the recently imposed restrictions on the use of DOTE, opening up new opportunities for using octyltin mercap- toacetate stabilisers,” Frenkel concluded. “Based on initial results obtained in accordance with the similar re-testing protocol, the global regulatory outlook is positive for not only the octyltins but also for the corresponding methyltin- and butyltin mercaptoacetate stabilisers.” Tin systems are used for almost all-rigid PVC
applications in the US; in Europe the main usage is for rigid, transparent applications. In addition to maintaining high transparency, tin stabilisers provide a very good early colour (no yellowing) and good colour retention. In non-transparent applications, tin stabilisers are particularly suitable where light colours are required, or when process requirements are demanding (thick plate extrusion and furniture films, for example). Tin stabilisers are also said to provide very good processability with high throughput and no plate-out. They are approved for use in food contact applications and potable water applications – and some are ap- proved for use in rigid medical applications.
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