TECHNOLOGY | FUNCTIONAL FILLERS
say. “Under this condition, only small nanoparticle content is required to enhance mechanical and transport properties of polymers.” Processing is not challenging. Romo-Uribe says
the efficient dispersion of POSS into PE was achieved using conventional twin-screw extrusion machinery and films were produced on a standard blown film line. He adds that the very low amount of POSS needed to significantly enhance the mechani- cal and transport properties of the PE keeps cost down and makes POSS a highly competitive additive. The compound is also recyclable. The reduction of oxygen transport opens
Above: Hybrid Plastics has found part- per-million additions of POSS can improve
mechanicals and reduce OTR of PE packaging films
single nanocage unit is the key to the mechanical reinforcement. Transmission electron microscopy is said to have showed that the POSS size was smaller than the empty space in the macromolecular web and so POSS intercalated the macromolecular web and mechanically reinforced without acting as a stress concentrator. “Furthermore, the entanglement intercalation and consequent reduction of empty space in the macromolecular web induced reduction of oxygen transmission (OTR) through the films. That is, POSS acted as a nano-plug filling the empty space (free volume) that macromolecules cannot fill,” they say. This OTR reduction is shown in Figure 5. Hybrid and J&J believe that the dispersion of POSS nanocages at the near single cage unit level lies at the heart of polymer nanocomposite performance, and large concentrations > 3 wt%) are unnecessary. In fact, they point out that at high concentrations the POSS cages can aggregate and even produce gelation, which may degrade the desired rheological and thermo-mechanical effects. “Dispersion at near unit-level takes advantage of the high surface area and volume of POSS,” they
Figure 4: Effect of addition of POSS to PE on modulus
opportunities for a single-layer packaging material, Romo-Uribe believes. “These findings offer a new paradigm in polymer nanocomposites formulation and establish the need to match nanoscopic particle size to polymer network dimensions in order to achieve optimal design of engineering property enhancements,” he says. “Furthermore, the implications of this study are broader as nanosize and dispersion are the key factors for mechanical reinforcement. Therefore, the same principles of properties enhancement apply to POSS mixed with diverse polymer hosts as long as the nanoparticle is dispersed to a size capable to intercalate the macromolecular web.” Hybrid Plastics says it is now working with a number of partners to explore application of the concept. “Packaging is one natural market but the field is wide open to novel applications,” says Romo-Uribe. Hybrid and J&J say that work so far has devel- oped and proved a concept, the dispersion of POSS at nearly single unit in a polymeric matrix. “Essentially, we have demonstrated that using large amounts of nanoparticles to reinforce polymers is a myth,” they say. “This work is at fundamental level
Figure 5: Effect on oxygen transmission rate of addition of POSS to PE. Blue bars show results for just- processed films; orange bars for films aged 18 months at room temperature at 30 to 40 % relative humidity
Source: Hybrid Plastics/J&J
40 COMPOUNDING WORLD | June 2020
Source: Hybrid Plastics/J&J
www.compoundingworld.com
IMAGE: SHUTTERSTOCK
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