Machine Design

New raw material for plastics: plant sugars

A new polylactide (PLA) resin is said to be the first natural-based polymer to compete against traditional packaging materials both in performance and cost. Called NatureWorks PLA, it is made from processed plant sugars by Cargill Dow Polymers LLC., Minnetonka, Minn. The polymer consists of chains of lactic acid, a natural food ingredient produced by converting plant starch into sugars. It is fermented and polymerized to form the PLA resin.

PLA resins are designed for clear applications and are said to have gloss and clarity similar to polystyrene with stiffness, tensile strength, and elastic modulus comparable to polyethylene terephthalate (PET). They also biodegrade like paper under simulated composting conditions.Other PLA polymers under development include an extrusion and thermoforming grade suitable for dairy and food containers, food serviceware, and cold drink cups. A biaxially oriented film is also available and has good twist and deadfold properties, making it a good candidate for candy twistwraps and other packaging applications.






Typical materials properties for PLA polymers

PLA resin

Specific gravity1.21D792
Melt Index, g/10 min (190°C)10 to 30D1238
Tensile yield strength, psi (MPa)7,000 (48)D638
Tensile elongation, %2.5D638
Notched Izod impact, ft-lb/in. (J/m)      0.3 (0.16)D790
Flexural strength (MPa) 12,000 (83)D790
Flexural modulus (MPa)555,000 (3,828) D790
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