Part 1 of this article focused on DSM's innovation strategy for composites and its work in the areas of renewable raw materials, life cycle assessment, and the elimination of hazardous substances. Part 2 covers cobalt-free curing, alternatives to styrene and GMP.
Cobalt-free curing systems
Anticipating increasing environmental pressure on cobalt, DSM has been working on the development of cobalt-free resin curing systems for many years. The company successfully scaled up the technology and filed a broad range of patents covering many types of accelerator systems and materials.
Cobalt octoate is the main component used today in accelerators for curing unsaturated polyester and vinyl ester resin, either incorporated in the resin (so-called pre-accelerated resin) or added separately to a non-accelerated resin.
In August 2012, cobalt octoate was reclassified as CMR2 by the Cobalt REACH Consortium. Other cobalt salts (including cobalt chloride and cobalt diacetate) were already reclassified as CMR 1B in 2011.
DSM introduced three new cobalt-free pre-accelerated resins to the market in 2012, with many more to come in 2013. These resins include Atlac® 580 A10, Atlac 580 A20 (both vinyl ester resins), and Synolite™ 7877-P-1 (an unsaturated polyester resin).
In 2012, DSM and AkzoNobel announced the introduction of the BluCure™ brand. The BluCure brand and Seal stand for 100% cobalt-free and true sustainability. BluCure products are either cobalt-free accelerators or cobalt-free pre-accelerated resins and meet the following strict criteria:
- 100% cobalt-free;
- easy-to-use in composite manufacturing processes; and
- not labelled as mutagenic, carcinogenic or toxic to human beings.
In terms of overall mechanical, thermal, and chemical resistance properties, cobalt-free laminates based on BluCure technology have similar performance characteristics to their cobalt-containing equivalent. For some accelerators and resins it has been found that the new systems can even give a better cure than the cobalt-containing reference resulting in a faster buildup of Barcol and reduction of residual styrene. In some applications this may eliminate the need for post-cure.
(For more information about cobalt-free curing see the feature Cobalt-free curing takes off.)
BluCure is the first cobalt-free curing technology in the world for ambient temperature cure. Through sub-licensing it is immediately and easily accessible to all composite component and resin manufacturers around the world.
Alternatives to styrene
In unsaturated polyester and vinyl ester resin systems the reactive diluent predominantly used is styrene. In June 2011, the US Department of Health listed styrene as a “reasonably anticipated human carcinogenic,” based on an assessment of publicly availability toxicity data. So far this has not (yet) resulted in a change to worker’s exposure limits. (See ACMA opposes listing of styrene as 'reasonably anticipated’ carcinogen.)
In Europe, discussions on carcinogenicity concluded in 2007 that styrene is not classified for human carcinogenicity. It has been demonstrated that workers can safely work with styrene under specific conditions. This involves using the correct protective equipment and not exceeding guideline exposure times. Meanwhile, in December 2012, the European Committee for Risk Assessment (RAC) adopted 15 opinions for harmonised classification and labelling (CLH), including one for styrene monomer. The RAC agreed to classify styrene as “causing damage to the hearing organs through prolonged or repeated exposure via inhalation,” and as “a substance suspected of damaging the unborn child (Reprotox 2).” The final decision for proposals for harmonised classification and labelling, and other proposals, will be taken by the European Commission through a committee procedure.
The composites industry has been minimising styrene emissions by using resins with additives that reduce styrene evaporation, using low styrene resins, and taking care of air quality in the working environment (e.g. by using air ventilation systems). Resins with a reduced content of styrene can provide a temporary relief, and they will help reduce styrene emissions to some extent. Meanwhile, it is fair to say that the listing in the US is still a very important milestone towards creating an environment where hazardous substances will be less tolerated, and where more efforts will need to be undertaken to develop cleaner, more sustainable materials.
In the pipe relining sector styrene-free has been on the radar for a number of years. There has also been a lot of interest in applications in the marine, automotive, food and construction industries. Here, closed mould systems have been developed to protect workers’ health and safety (e.g. vacuum infusion techniques, and hot cure SMC/BMC processes). Meanwhile, for traditional processing techniques like hand lay-up and spray-up we see that customers are looking for solutions to minimise and preferably eliminate styrene emissions. DSM is actively working on the development of such resin systems.
(See DSM launches range of styrene-free resins.)
In the styrene-free resins systems currently offered by DSM alternative reactive diluents are used, typically based on methacrylates. Apart from the lower (or in some cases close-to-zero) emissions, these can help create unique system performance, while being safe to use and not suspect in terms of human toxicity. A key challenge is to maintain the advantages associated with the robustness in processing offered by styrene-containing resin systems, and to find a solution that can come close in terms of cost.
Styrene-free resins will have slightly different characteristics than styrenated resins, simply because the chemical composition is different. In some cases performance is better (e.g. the chemical resistance of DSM’s Atlac Premium 600 resin against organic solvents when compared with Atlac 430 resin), and sometimes it is slightly worse.
Styrene-free resins will have slightly different characteristics than styrenated resins, simply because the chemical composition is different. In some cases performance is better, ... and sometimes it is slightly worse. |
Selecting the right methacrylates in combination with optimisation of the resin backbone chemistry has shown to be the key for achieving the right system performance. It is clear that material systems used to repair industrial storage tanks will require a different technical solution than a system to repair drinking water pipelines. Also, that in some markets and application, avoiding liabilities and reducing product risk can outweigh the higher initial cost of styrene-free resin systems.
The discussion about the hazardous properties of styrene has been ongoing for decades and still has to reach a conclusion. So we need to be realistic about the pace of change. However, once a viable styrene-free technology becomes available, the likelihood that customers will want to implement such a sustainable solution will definitely increase. It is fair to say that the US NTP listing and the new proposed CMR2 reclassification are very important milestones towards creating an environment where more efforts will need to be undertaken to develop cleaner, more sustainable materials.
Introduction of GMP
Pipes, vessels and storage tanks operating in direct contact with food or drinking water require compliance with specific European standards and regulations. While enabling food processing and drinking water operations to run more smoothly as a result of the durability and resistance to chemicals of vinyl ester and unsaturated polyester resins, DSM is supporting the industry in creating products that are safer to use. Since 2011, DSM has introduced many resins that are made according to GMP and European Framework Regulation 1935/2004, and that are compliant with the ‘positive list’ (list of allowed materials) of the European Food Contact Directive 2002/72/EC and European Commission regulation 1895/2005.
(See Resin meets European food contact regulations.)
GMP is the internationally accepted quality control system used in the nutritional, food and pharmaceutical industries that sets standards and guidelines for the safe production, testing and use of a product. GMP ensures that materials and parts are made consistently at a high quality level, and that all the right precautions are taken for avoiding cross-contamination.
For composite components in contact with foodstuff there is a clear legislative requirement to have GMP in place. |
For composite components in contact with foodstuff there is a clear legislative requirement to have GMP in place. Consequently per the recommendations of Plastics Europe, production of food contact ‘materials’ (i.e. base materials as well as finished components) shall be done according to GMP, particularly if both food contact materials and non-food contact materials are produced in a factory and there is a risk that cross contamination can harm the quality of the food contact materials.
For components in contact with drinking water the requirements are less defined: many local regulations in individual EU countries require testing and certification of components. By using resins that have been made in line with GMP, manufacturers of components for drinking water contact will obtain faster certification of their parts and can better control their production process, as the resin system simply does not contain hazardous components that may leach out.
DSM can help customers by auditing their plants and proposing process improvements (manufacturing procedures, dedicated equipment, cleaning and traceability). Certifying that the ingredients of GMP resins are compliant with the ‘positive list’ simplifies the approval process for DSM’s customers. Thanks to these resins, getting the approval for the final components which are manufactured from these resins is easier, quicker and can be achieved with reduced testing.
Conclusion
DSM believes that its continued success will be driven by its ability to create shared value for all stakeholders, now and in the future. DSM creates sustainable shared value by innovating in ways that allow its customers and other stakeholders downstream in the value chain to provide better People, Planet and Profit solutions − solutions to the challenges facing society, the environment and end-users. ♦
- Read Part 1 of this article here.
Further information
Thomas Wegman, Marketing Manager, DSM Composite Resins; e-mail: thomas.wegman@dsm.com
Robert Puyenbroek, Gobal R&D Director, DSM Composite Resins; e-mail: robert.puyenbroek@dsm.com
This article was published in the January/February 2013 issue of Reinforced Plastics magazine.
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