Technical Papers Plastics
New PLA features higher HDT and impact, drying solutions for processing PLA resin

New PLA features higher HDT and impact, drying solutions for processing PLA resin

Improved impact strength and heat deflection temperatures in polylactic acid (PLA) could result in the material becoming a candidate for injection-molded, semi-durable and durable applications. The bioplastic is also now better suited for high-end disposable food service items such as cutlery, coffee lids and containers for microwavable products. The base polymers for Terraloy BP-34001 products are Ingeo resins supplied by Nature Works. Since these compounds dramatically improve the heat and impact resistance of PLA while largely retaining the environmental benefit of this polymer as a bio-plastic, they promise to expand the applicability of PLA, making possible new uses in higher-heat food service items as well as consumer goods. Teknor Apex has overcome an inverse relationship between heat distortion temperature (HDT) and Izod impact strength in PLA, creating a new series of compounds, Terraloy BP-34001, that provide up to 2 times the HDT and up to 6 times the impact strength of standard PLA resins. Other benefits to the newly developed PLA compound include:
In comparison with previous enhanced-performance PLA resins, the new Terraloy compounds process faster - cycle times are 28-30% shorter.
The compounds incorporate a larger percentage of renewably resourced content, about 10-30% more. Nearly all of the new Terraloy compounds are said to comply with FDA requirements for food-contact applications.
In property tests, a typical grade in the new series, Terraloy BP-34001D, exhibits a heat distortion temperature of 112° C and Izod impact strength of 135 J/m. By comparison, approximate values for standard PLA are 65°C and 33 J/m. The new compound complies with FDA 21 CFR requirements and has a renewable content of 78%.

Una-Dyn have resolved issues associated with the pre-drying of PLA (Polyactic Acid) resin prior to processing PLA extruded sheets used for thermoformed packaging and PLA injection moulded preforms as used for PLA bottles. PLA resin is being increasingly used in packaging applications and is derived entirely from renewable resources such as corn. Virgin PLA resin is crystallized and dried to 400-ppm moisture level prior to leaving the production plant. The drying process of the PLA resin is the most critical stage of the raw material preparation, as 250 PPM or less water content is necessary to ensure product quality. This can only be accomplished with the tight control of temperature, with the corresponding exposure time and air quality. The equipment required to dry PLA consists of a Dehumidified Hopper Dryer with high temperature process options. There are four principle factors involved.
• Adequate airflow is necessary to carry thermal energy to the resin, and provide sufficient air exchange to carry away all of the moisture.
• The dryness or dew point of the air entering the hopper must be -40°F dew point. The reason for the low dew point is to enable any water content of the resin to move immediately to vapour and be carried away on the process airflow.
• The selection of a proper drying temperature is critical to ensure the resin does not fuse in the vessel, while still ensuring that it removes all water. The normal temperature is 160�F for four hours.
• The drying hopper used is the most important element. If the vessel is too small, the resin will not dry properly, alternatively if oversized, it could melt the resin. The hopper must also provide equal treatment of each pellet that enters the vessel. The best quality dry air is only useful if it is distributed to each pellet being dried, and the air diffusers must move the air equally to all parts of the vessel.
 
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