PP transparent – how does it work?
A number of mechanisms occur when polypropylene (PP) transitions from the melt phase to a solid state. As such, it is interesting to examine these mechanisms carefully under the microscope and to analyse them in more detail. The graphic shows how a solid polypropylene production part is deconstructed to its smallest constituent parts, lamellae, representing a jump from a visible size in centimetres to a size in the range of several angstroms [0.0000000001 metres]. This provides a good example of the scale of magnitude we deal with when processing polymer materials – and of what effects even the smallest of changes can have. With all this said, how do so-called nucleating agents and additives work to raise the degree of transparency? And most importantly of all, what is actually modified – and how?
What is the mechanism at work?
What’s essentially happening is the formation of so-called “nucleation seeds” during the solidification of the polymer. These are usually either defects along the polymer chain or foreign particles in the melt. Spherulites are formed around the nucleation seeds during the cooling phase, with the effect that PP consists of both crystalline and amorphous regions in a percentage ratio of around 60:40 following complete solidification. There is a critical state during the cooling phase that occurs between 148°C und 106°C depending on the type of polypropylene. In this state, additives effect a change in the crystallisation process as well as an agglomeration of polymer chains in the solid state. They raise the crystallisation temperature and the degree of crystallinity whilst simultaneously bringing about a reduction in the size of the spherulites.
How are these additives used?
It’s important, in the first instance, to differentiate between nucleation and an increase in the degree of transparency. When classic – generally inorganic – nucleating agents are added, PP spherulites are formed around these inorganic defects. This increases the rate of crystal growth, which in turn reduces the time required for complete solidification and enables earlier demoulding. The overall effect is that cycle times are sped up. Organic molecules are usually the additive of choice for effecting improvements in transparency. They work by fusing with the polymer. The better the distribution of these molecules and the more homogeneous the melt, the greater the reduction in spherulite size and the higher the degree of transparency. This is because small spherulites allow more light to pass through the polymer, which in turn reduces the “haze value”.
What are the results?
Alongside the above-mentioned reduction in cycle times, the effects of these additives include an improvement in rigidity and – depending on how the additives are used – a partial improvement in scratch resistance. Combined with the high cost-benefit ratio offered by our masterbatch approach, these improved structure-property relationships play a pivotal role in guaranteeing the efficient production of injection moulding parts, packaging and functional parts.
Interested in this product?
We offer the possibility for various active ingredients to be combined in a formula that’s tailored directly to your intended application and produced as a masterbatch. This allows you to benefit from optimal levels of homogeneity and the best possible properties. You determine the application and save costs as a result of being able to rely on standard polymers. This option is perfect for applications where high levels of rigidity and scratch resistance are required. Resulting products are approved for applications in contact with food and conform to the relevant statutory regulations. Get in touch for more information!