Purging materials: protecting the environment and saving energy
Huge volumes of plastic resins are wasted every day due to product contamination and ineffective changes to resin and/or colour. This large amount of plastic scrap has a significant effect on the environment. As a result, THE PROBLEM OF PLASTICS is a recurring topic in newspapers, television and other media.
FIG 1: The first shots of processed pieces with so-called stripes
POLYMERS AND THEIR “LONG LIFE“All polymers are generated from hydrocarbons or their derivatives, which originate from crude oil or biological sources such as cellulose, fatty acids or other sources. The chemical bond carbon-carbon and the other chemical bonds (C-N, C-H, C-O etc.) on which a polymer is based, remain very strong and stable over time. As a result of this feature, polymers have a long life, and are also weather resistant and extremely strong. This is why we can find them almost everywhere in our daily life in the form of various objects. But unfortunately, in addition to these positive features that make them suited for use in industry, they have a very low degree of biodegradability and consequently a significant environmental impact. Due to this fact, it is very important that they are not thrown away, but recycled and re-used. We also think that it is important that as few virgin polymers as possible are turned into waste material before they have fulfilled the function for which they are processed.
A polymer cannot be recycled indefinitelyWhen a polymer is heated for processing, the heat stress causes the molecular chain of the polymer to break and oxidize, resulting in a weaker molecular structure and therefore weaker chemical-physical features. During the first processing this heat stress is not so important, because almost all polymers already contain stabilizing additives. But if production becomes waste before entering the end-users market, these polymers must be properly recycled.
Production costsWhen changing from a dark colour to a clear colour, the first shots of processed pieces have so-called stripes, or other kinds of contamination stemming from previous production. These shots cannot be reused for other clear colours and are typically reground in order to produce black or very dark coloured pieces (figure 1). As not all companies produce large quantities of dark pieces, it is often necessary to recycle them. If we consider that a certain first choice virgin material has a price X, requires a certain quantity of electric energy E for its production, requires machine and operator time T, as well as regranulation time Tr and a quantity of energy for regranulation Er, in order to obtain a final product, which is decreased by the value Xr as compared to the initial product price, we observe a time and capital loss Ls (loss due to scraps) which can be quantified as follows :
-reduce the waste production -increase the production duration -improve the regeneration process for scraps In our opinion, point 1 is the best way to reduce the production costs, as it is not always possible to influence points 2 or 3. Modern purging compounds make it possible to produce between 2 and 200 times less waste during colour and/or material changes. Therefore we can now add a variable for the purging compound to our equation, considering the cost for the purging compound Xpu, the energy Epu and the time Tpu
including hot runners With the following benefits -Less wear on process equipment -More productive use of labour and materials -Fewer product defects - less scrap reprocessing -Up to 90% less downtime -Improved performance -Ammonia, silicon and wax free -No need to dismantle equipment