Thermoplastic polymers mean serious business: in 2008, the global market for Polypropylene had a volume of 45.1 million tonnes, which led to a turnover of about $65 billion.
DMDBS, or dimethyl dibenzylidene sorbitol, is a butterfly-shaped molecule that is used as a nucleating agent in the manufacture of Polypropylene (PP).
PP is a commercial engineering plastic that is tough and flexible and is used in numerous products from packaging to textiles to banknotes. It can be tailored to specific applications during manufacture making it very versatile. Despite being commonly used, the relationship between how the material is synthesised and processed, and its physical properties is unclear. As a result, scientists are continuing to study this popular material.
Guruswamy Kumaraswamy, and a group of scientists from the National Chemical Laboratory (NCL), India, have used a Linkam TST350 Stage to look at the influence of this molecule on the mechanical characteristics of the plastic film. DMDBS precipitates out of a hot melt of PP and forms crystalline nanofibres which form a mesh. At cooler temperatures, PP crystals nucleate on the surface of these nanofibres.
PP pellets were coated with DMDBS using a DMDBS solution in acetone. These pellets, with 0.2%, 0.4%, or 0.8% (by weight) DMDBS were used to create a film of a constant thickness of 0.45mm. These films were tested using the Linkam TST350 stage.
It was observed that at TDIE=200°C voids form within the 0.8% DMDBS film during extrusion. This, the scientists hypothesized, was the reason why the 0.8% film exhibited a decrease in yield stress and modulus values compared to neat PP film and the 0.2% and 0.4% film. The 0.2% and 0.4% DMDBS PP film exhibit a ≈50% increase in modulus and yield strength compared to neat PP.
So in summation, a low concentration of DMDBS (0.2, or 0.4% DMDBS) created a stronger film, but higher concentrations (0.8%) had a negative impact on the film strength.
By Caroline Feltham