Adding stability and durability to polymers

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By adding more polymers to vehicles in order to save weight and increase the green credentials of their vehicles, OEMs are potentially building in a new set of challenges. Polypropylene (PP)-based materials and other plastics need to be stronger, more environmentally sustainable, lighter and more durable than ever before.

One of the leaders in the field of polymer stabiliser developments is Songwon of South Korea, while Sabo is a key player from Italy in the area of light stabilisers.

Thomas Schmutz, Director Global Technical Service at Songwon, and Arnim Helmboldt, Marketing Director from Sabo, explain what they see as the main trends in the automotive industry.

What are the trends on the demand for polymers in the automotive sector?

Schmutz: There are a number of convergent trends that have a direct impact on the demand for polymers. The pressure on OEMs to reduce costs is higher than ever after the 2008 financial crisis. Together with being able to meet the demands of mass production comes the need to reduce development time. OEMs want to unify platforms – which allows for the faster development of new cars – while at the same time having maximum flexibility when it comes to design. The purchase of a car remains an emotional experience.

Environmental pressures keep OEMs focused on weight savings in order to reduce CO2 emissions, and to increase the use of recycled materials. We see more and more recycled resins being used in vehicle manufacturing. Our challenge is to develop products that leave no deposit on the windshield, do not smell, do not degrade throughout the life cycle, and are more cost-effective.

There is a trend to replace the more expensive polymers such as styrenes or engineering polymers with polypropylene (PP), and to substitute PP with polyethylene (PE) because the availability of shale gas is widening the cost gap between these two polymers. There is also a move from the heavier polymers such as PVC or styrenes to lighter weight polymers such as polyolefins.

What are the key trends in the automotive industry where Songwon additives can have an impact?

Schmutz: Some of the key trends in the automotive industry where Songwon additives can have an impact include weight savings. For instance, 100 kg weight reduction yields up to 10 g/km reduction of CO2 emissions. We have solutions to help OEMs reduce weight further by making a solid wall thinner. A reduction in thickness decreases intrinsic stability, and this can be counterbalanced by the use of more (or better) stabilisers.

Factors that need to be taken into account include reaction between the stabiliser and blowing agents, and the absorption of additives by the fillers, which means that the additives are as a result not available in the polymer matrix to protect the polymer. Our additives also ensure that there is no degradation throughout the life-cycle. Thermoplastic polymers such as PP, TPO, PE, PUR, PVC, and styrenes would not be suitable for automotive applications without stabilisers.

Stabilisers allow the OEM to guarantee components under the hood, as well as moulded exterior components for the life-time of the vehicle. The durability of plastics can be significantly improved with the right choice of stabilisers. This allows reduction of CO2 emissions and the use of fossil resources because fewer articles are manufactured.

When it comes to recyclability, downcycling can be delayed or avoided with early top-up stabilisation. Typically, stabiliser levels present in the polymer are not sufficient for the recycling process, and “top-up” stabilisation is needed.

New standards require new solutions. The industry standards on VOC, FOG and total carbon emission are changing drastically. State-of-the-art stabilisation systems are not able to meet these new standards.

Can engineering polymers be replaced with PP for under-the-hood applications?

Schmutz: Songwon’s Global Application Centre development facility in South Korea is in the process of developing a new stabilisation system. This concept targets to almost double the lifetime of PP at ageing testing temperatures of 150°C.

PP is very sensitive to thermo-oxidative degradation. There is severe degradation during melt conversion in the absence of stabilisers. Classical state-of-the art stabiliser systems reach only a certain performance level, because additives exceed solubility level in PP, and a further addition has only a marginal effect on the long-term thermal stability of PP. Our new concept will be able to overcome these limitations.

What is the right strategy to reduce volatiles and odours for car interior applications?

Schmutz: Classic stabilisation systems typically meet most of the long-term thermal stability criteria of the automotive industry. However, they have a number of limitations related to extraction resistance, interaction with filler materials, interaction with carbon black, resistance to external chemicals (eg. chlorine) , compatibility with selected UV additives, and indirect food contact (specific migration limits, SML).

To reduce volatiles and odours for car interior applications, Songwon is offering three strategies to overcome the performance limitations of the classic systems.

1. SONGXTEND 2121 stabiliser is able to meet the long-term thermal stability level of classic additive systems, while reducing the sulphur content by 60%.

2. SONGXTEND 2122 stabiliser equals the long-term thermal stability level of classic additive systems. The reduction of the sulphur content is 30%, and the system offers better cost performance.

3. SONGXTEND 2123 stabiliser is a completely sulphur-free system, which means it is odourless. The system cannot meet the long-term thermal stability performance level of the classic sulphurbased system, but is better than the next-best alternative.

How can an additive supplier make a car bumper formulation more cost efficient?

Helmboldt: Light stabilisation formulations for car bumper systems based on TPO were established many years back. However, the requirements for increased light stability combined with ancillary properties, such as no blooming of the additives and excellent paint adhesion, persist.

Sabo offers SABOSTAB UV 70 and SABOSTAB UV 91 50PP light stabilisers, two of the products largely used in automotive applications.

Sabo entered into a distribution partnership with Songwon for its light stabilisers last year. The product ranges of Sabo and Songwon complement each other perfectly. Our partnership extends to joining resources in R&D. The outcome of the joint development resulted in new solutions for automotive applications.

The products represent synergistic blends with SABOSTAB UV 228 50PP dedicated for interior applications and SABOSTAB UV 210 outperforming standard UV stabilisers in automotive exterior applications like TPO bumpers, when criteria like surface and colour protection and gloss are key quality requirements.

What is the right light stabiliser solution for an automotive interior application meeting the more stringent requirements of the automotive industry on VOC/FOG and total carbon emission?

Schmutz: The automotive industry recently changed the requirements of FOG. One of the reasons for this change is that nowadays new cars are stored outdoor for a couple of months, in case the market slows down, and the off-take of the car dealers is reduced. Volatiles coming from additives in the polymer settle as a deposit (FOG) on the interior windscreen. This needs to be removed manually before the car gets sold, which adds to the costs. The other reason for reducing volatiles in the car interior is the reduction of odour. Again, in most cases low molecular weight components of the polymer or additives are the major contributors.

Helmboldt: The Songwon/SABO partnership understands the needs of the automotive industry very well and in addition to SABOSTAB UV 228 50PP light stabiliser further solutions for interior applications are under development. Our light stabilisers and new solutions offer excellent light stability for applications such as dashboard, door panels, rear shelf and others. They are also able to meet the new requirements of the automotive industry in terms of low VOG, FOG and total carbon emission.

(IMA)

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