Global plastics demand
There are a variety of radicals which can generate polymer radicals including alkyloxy, phenyl, methyl, acyloxy and cumyloxy. In reactive extrusion the peroxides are combined with the base polymer and the reaction occurs in the extruder followed by degassing. Crosslinking improves properties such as impact and stress-crack resistance, temperature and chemical resistance. In the cable industry there is a shift to in-house compounding for medium voltage (MV).
Sustainability is a key issue worldwide. RockTron is using fly ash from waste incineration to produce fillers. The MinTron particles comprise solid glass spheres and the product is developed to customer specifications, for example from 5-9 microns or 8-14 microns. MagTron is a spherical magnetite particle measuring 55 microns CenTron is hollow glass spheres of 140 microns. Surface modified grades are available and these products are being used as fillers.
The foaming process comprises several steps starting with nucleation, then bubble growth and stabilisation. A crosslinking agent can be added after foaming. Polimeri Europa is testing blends of polyethylene and EVA in foams and comparing properties at different percentages. The vinyl acetate content has a big influence on the final foam properties. LDPE and LLDPE are used in blends to improve the performance of both, for example LDPE is easier to extrude and LLDPE is more heat resistant.
A new EU plastics regulation came into effect on 1st May 2011. Keller and Heckman have reviewed the implications for the industry, for example, here are some of the definitions:
Article 3(8). Additive, “a substance which is intentionally added to plastics to achieve a physical or chemical effect during processing of the plastic or in the final material or article; it is intended to be present in the final material or article”.
Article 3(8). Polymer production aid (PPA), “means any substance used to provide a suitable medium for polymer or plastic manufacturing; it may be present but is neither intended to be present in the final materials or articles nor has a physical or chemical effect in the final material or article”.
Article 3(9). Non-intentionally added substances (NIAS) are defined in “means any substance used to provide a suitable medium for polymer or plastic manufacturing; it may be present but is neither intended to be present in the final materials or articles nor has a physical or chemical effect in the final material or article”.
K-Tron has reviewed the issues with material quality and additive dispersion. The company recommends implementing quality control on deliveries and making sure that equipment is functioning to the required standard. It is important to consider the history of the material and factors such as storage conditions, thermal exposure and mechanical treatment, which can cause problems like particle agglomeration. During conveying there can be issues with many aspects including the amount of air coming through and build up in the connecting pipes. The whole system needs to be set up correctly for each new operation.
Dr. Oleg Kulikow of the Universität Der Bundeswehr Munchen has studied polymer processing aids (PPA): these have greater adhesive properties to metal than molten polyolefins and form a lining at the die surface during extrusion. Hydrophobic materials like fluoropolymers are often used as lubricants, however in natural joints the lubricant is hydrophilic. A new PPA is proposed comprising polyethylene glycol and silanol, and relatively cheap to produce.