DuPont Entira EP is a new series of compatibilizers which have been designed to aid the recycling of difficult-to-separate mixtures of inherently incompatible polymers. The first grades which have now become available in the market are ethylene-copolymers, optimized for mixed waste streams of polypropylene (PP) and polyethylene (PE). DuPont says it is currently developing further formulations of compatibilizers for other mixed materials, including PE and polyamide (PA) or PE and ethylenvinyl alcohol (EVOH), which are typically used as barrier resins in polyolefin based packaging films, bottles or rigid containers, and therefore available in high quantities worldwide. Additional interest is also being shown, claims the group, in PE-PET mixtures with PE as the dominant matrix – a mixture that emerges in the beverage industry.
Compounding of reground mixed polymers together with Entira EP in a twin-screw extruder (or in a single screw extruder with good mixing performance) is said to generate recyclate in pellet form with excellent mechanical and processing properties, even where high degrees of contamination are present.
The compounding process itself may also be made more economical, because using Entira EP reduces the need for melt filter cleaning.
Depending on the selected compatibilizer formulation, the compounded material can reach almost the same level of low temperature toughness as the major blend fraction, claims DuPont. The granulate produced is suitable for injection moulding, extrusion or blow moulding. Typical applications include use as blending partners in new materials or as core layers. DuPont says that under certain conditions they can even be processed directly.
“As plastic processors increasingly recycle plastic waste in-house, the amount of single-component and therefore easy-to-process material available to the recycling industry is going down”, comments Michel Decodts, Market Segment Leader at DuPont. “At the same time, incompatible plastic mixtures have become more readily available. These have to be segregated at relatively high cost and therefore make it more difficult to achieve specified recycling rates. Entira EP compatibilizers now offer manufacturers of re-compounds cost-efficient new opportunities, as they significantly boost the range of ready-to-use raw materials for high-performance applications.
Typical sources for mixed PP-PE waste streams include packaging applications, such as screw-caps made of PP and fitted with sealing inserts made of foamed PE. Products resulting from mixing and jointly processing such incompatible plastics in an extruder consist of a continuous phase (the matrix), created by the higher fraction material, and inclusions of the other component dispersed in this matrix. Adhesion between the matrix and the inclusions is poor, cracks may easily propagate along their interfaces, and mechanical properties are therefore on a very low level.
The new PE-PP-specific Entira EP formulations are ethylene-copolymers, exhibiting high compatibility – and hence adhesion – to either one or to both polyolefins. Even at low concentrations of around 4%, these new compatibilizers act highly efficient, promoting a firm bond between matrix and dispersed material. Best results will derive from an advanced formulation which provides good compatibility to PE and at the same time to PP. Here cracks will propagate through both the PE and the PP rather than along their interfaces, increasing strength, elongation at break, and in particular low temperature impact strength of the re-compounded materials to a level which even meets most stringent requirements.
Loic Rolland, Technical Development Leader at DuPont Packaging & Industrial Polymers, said: “Entira EP compatibilizers provide new opportunities for generating added value by recycling used plastics, and help reducing the need for landfilling or incineration. They support the production of re-compounds with excellent processing and in-use performance even from highly contaminated feedstock. Our tests have shown mechanical properties to reach levels, which can normally be achieved only after applying costly separation technologies to provide extra low contamination grades. Therefore, re-granulates compounded with Entira EP are even suitable to mould high-performance, thin-walled components.”