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Impact Case Study

Plastics combine forces to create super-polymer

Glass fibre reinforcement helps bring together two household plastics to form a tough new composite material.

22 September 2018

Two of our most common and versatile plastics could find an even broader range of applications by blending them into a single material, research from KACST suggests. By combining the polymer used to make plastic drinking bottles, with the polymer used to make flexible tubing and cling film, the researchers have produced a super polymer that offers some of the best properties of both materials. 

The plastic bottles filled with water or juice, that you might pick from a supermarket shelf are typically made from a polymer called polyethylene terephthalate (PET). It is strong, stiff and has good oxygen barrier properties that help to preserve the flavour and nutrition of the drink inside. At the checkout, the plastic bag you might place the bottle in is often made from linear low density polyethylene (LLDPE), which is tough, flexible and puncture-resistant. 

Attempting to mix PET and LLDPE to create a hybrid polymer has proven very difficult, however. Trying to blend a molten mixture of the two plastics is like trying to mix oil and water; the two polymers are highly immiscible. Chemical ‘compatibilizers’ can be added to the mixture to help them blend, but these additives tend to drastically reduce the stiffness of the resulting polymer. 

A new method for blending PET and LLDPE without compromising the resulting polymer’s stiffness has now been developed by Fares Alsewailem from the National Center for Petrochemical Technology at KACST and his colleagues. The team used glass fibres—a material often used in reinforced composite materials—and were able to produce thermally stable polymer blends with good mechanical properties. 

The researchers systematically investigated the glass fibres’ impact on the composite material’s properties by creating 17 different polymer blends incorporating different proportions of PET, LLDPE and glass fibre. By studying the resulting blends using scanning electron microscopy, the team showed that increasing the glass fibre content resulted in improved bonding between the fibres and the polymer matrix. 

The good microstructure of these glass fibre-enriched blends seemed to translate into enhanced mechanical properties, Alsewailem and his team went on to show. An 85:15 blend of PET:LLDPE, reinforced by a 15 percent or 30 percent addition of glass fibre, had a comparable tensile strength and better impact strength than pure glass fibre-reinforced PET, for example. 

Glass fibre reinforcement could become a good method for making high performance blended polymer composites, the research suggests.

References

  1. Alqaflah, A. M., Alotaibi, M. L., Alghamdi, M. S., Aldossery, J. N., Alsewailem, F. D. Preparation and characterization of glass fiber–reinforced polyethylene terephthalate/linear low density polyethylene (GF‐PET/LLDPE) composites. Polymers Advanced Technologies 29, 52­–60 (2018). | article