05/11/2016 The first challenge encountered by processors of bio-resorbables is material handling, which is the single largest area for error. Today we will be discussing micro molding in bio-resorbable PLA and PGA materials. There are many different compounds of PLA/PGA. Most common is the 82/18 version (82% lactide, 18% glycolide). A very high concentration of glycolide creates material handling and feeding difficulties due to the “gooey” nature of the glycolide. An abundance of information can be found using several of the bio-resorbable polymer suppliers (Purac, Boehringer Ingelheim, Lakeshore, DSM to name a few). When it comes to micro molding, however little information is available on the market due to proprietary processing techniques and lack of industry-specific testing for custom compounds.
PLA/PGA materials are highly susceptible to moisture and heat. They must be stored properly (usually in a freezer) at a specified temperature in nitrogen-sealed foil pouches. They must then be used according to the processing run quantities needed and material drying cycle. The material usage must be matched with the injection screw and shot size in an injection molding machine so that the material is not sitting in an improperly sized machine where over-drying and over-heating can occur due to the prolonged temperature and drying exposure. This makes micro molding machines another key component to processing bio-resorbable polymers. Because they are highly shear and heat sensitive, proper fit of the shot size for a micro molded part to the screw and barrel is critical. The residence time (time the polymer sits in the barrel) can affect the IV (Intrinsic Viscosity) of the material. Small shot sized machines are typical in the design of micro molding machines. Some machines use reciprocating screws and some use screw over plunger technology. Some other machines are being developed by processors of bio-resorbable materials because even the smallest shot sizes available on the market are too large to properly process small amounts of bio-resorbable polymers. These machines are typically proprietary and primarily usesdinternally or through licensing agreements.
Many challenges exist in micro molding but there are ways to minimize these challenges and corresponding risk of failure to component manufacturers. In future blogs we will discuss other challenges in micro molding.