Plasticisers have a reputation. These additives, while crucial to many applications, have been a source of unrest as unsettling reports of the detrimental health effects of some plasticisers emerged. At the same time, it is fair to say that no other type of additive has been studied so intensively as plasticisers have been - mainly because of the ubiquity of their use. They are, in fact, among the most commonly used additives in the industry. Plasticisers are used in applications varying from medical and the automotive industry to fashion, building and construction. They offer flexibility and pliability to thermoplastic resins such as PVC; and serve to enhance processability and mouldability. Depending on the application and resin, they are used at levels that can be significantly higher than other additives - up to as much as 60% by weight. The global market for plasticisers is therefore huge: valued at $14.7 billion in 2020, it is projected to reach $22.0 billion by 2030, growing at a CAGR of 4.1% from 2021 to 2030.
As these additives are not bound to the polymer matrix, plasticisers are known to migrate out of plastics, into the environment, both outdoors as well as inside. For example, studies have found phthalates in indoor dust. As well, phthalates can potentially disrupt the endocrine system and have been linked to certain cancers and metabolic disorders. Their use is very strictly regulated in Europe.
Next to phthalates, other types of plasticisers include cyclohexane dicarboxylic acids, terephthalates, trimellitates, adipates, sebacates and organophosphates. Less is known about their effects of health and environment, and scientists have called for more research on their toxicological profiles and environmental impacts. By their very nature, these plasticisers are also not chemically bonded to their products, and like their more well-known phthlate counterparts, will also leach out from their source material - with potential toxic effects. Reports on some neurotoxic, oestrogenic and hepatotoxic effects have already started to appear.
As the general awareness in respect of safety and sustainability mounts, other alternatives are being explored. Demand for renewably-sourced plasticisers is on the rise, as these are held to have fewer harmful impacts on health and environment. Obviously, however, the fact that a substance is renewably sourced or biobased does not automatically make it a non-toxic, safe alternative, which is why here, too, more research is required.
Currently, the various alternative renewably-sourced plasticisers include are mainly based on vegetable oils and derivatives, castor oil, epoxidised soybean oil and esters. Established renewably-based plasticisers are, for example, isosorbide diesters, marketed as Polysorb ID by Roquette; DuPont-Danisco’s vegetable oil-based, food contact approved Grindsted Soft-N-Safe; Hallstar’s HallGreen collection of ‘environmentally responsible’ renewable esters for use in PLA, PHA, PSM and other bio-polymers; and Citrofol BII (tributyl O-acetylcitrate), which is described by its producer, Jungbunzlauer, as an efficient primary plasticiser for ‘sensitive applications under scrutiny due to no concerns in terms of toxicological, ecotoxicological and environmental reasons’.
Regarding the latter, the European Commission has stated that citrate and blends of citrate and vegetable oil derivatives are suitable plasticisers for sustainable cellulosic plastics, as ‘the risk assessment has provided sufficient evidence to show that toys plasticised by acetyl tributyl citrate can be safely mouthed by children’.
The abovementioned list of products is by no means comprehensive. Other companies, including Cargill, Lanxess, Dow and Avient - to name but a few - have also developed alternative plasticisers with biobased content and this market is also set to grow. A May 2022 report on the bioplasticisers market valued this at $1.3 billion in 2020, and is projected to reach $2.1 billion by 2030, growing at a CAGR of 5.31% from 2021 to 2030. (Bio Plasticizers Market, Global Opportunity Analysis and Industry Forecast, 2020-2030).
And in Japan, Takuhiko Jinno and Ryohei Mori at Green Science Alliance Co., Ltd, have announced they have developed and plan to commercialise what they claim is the first natural biomass, plant-based plasticiser made with lactic acid. According to Mori, the biomass content of new lactic acid plasticiser is about 55 – 60 %; Green Science Alliance will continue its work on the product, in order to increase its biomass content.