Compounding bioplastics | technical paper
Steve Maki, vice president technology at RTP, explores how melt compounding can increase the performance of biopolymers, allowing them to be used in more demanding semi- durable engineered applications
High performance biopolymers via compounding
Biopolymers should not be considered new and novel polymers. One of the earliest polymers used to replace ivory in billiard ball applications was the bio-based celluloid which was fi rst invented and produced from a mixture of cellulose nitrate and camphor by John Wesley Hyatt back in 1870[1]. The turn of the century, however,
ushered in the invention of synthetic polymers from petroleum feedstock, including Bakelite in 1907, and the trend has been to predominantly use petroleum sourced polymers ever since.
Over the past decade, our global society has become ever more concerned with the depletion of earth’s limited natural resources and the result has been the recent development of many new and novel polymers derived from bio-based, rapidly renewable resources. These include such polymers as polylactic acid (PLA), polyhydroxyalkanaote (PHA), poly-3-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and polyhydroxyhex- anoate PHH.
Of these new biopolymers, PLA – a bio-based
polyester – has gained the most commercial attention. Companies, such as NatureWorks, have developed and invested in the infrastructure and resources to provide numerous commercially available grades of PLA polymer – NatureWorks sells its PLA grades under the Ingeo trademark. The commercial opportunities for
Table 1. Typical properties of neat PLA Property
Notched Izod Impact HDT @ 455 kPa Tensile Strength
www.compoundingworld.com Value
15 J/m 55°C
60 MPa
RTP has developed a 2000 Series 30% glass-reinforced PLA grade for a scissor
handle application, replacing 30% glass reinforced PP. The grade has 68% renewable
content and is nucleated for improved cycle times. It
offers superior strength and stiffness compared to the reinforced PP
PLA, however, have been largely limited to the com- modity applications of clamshell packaging, disposable utensils, grocery bags, and disposable water bottles due to the inherent low physical properties of the neat polymer as shown in Table 1. For biopolymers such as PLA to take the next step
into commercial semi-durable applications, these properties must be improved to put them on par with the petroleum-based polymers including HIPS, ABS, PP, PC, nylons, and PBT. Compounders, such as RTP Company, have the technology to upgrade these biopolymers to engineering level performance by using the process of melt compounding. In order to determine if the physical performance of
PLA can be upgraded to a level that would allow it to compete with traditional petroleum based polymers used in many semi-durable applications, RTP set up a series of melt compounding trials that would address each of the polymer’s weaknesses.
March 2014 | COMPOUNDING WORLD 45
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