The chronic limitations of biopolymers include their susceptibility to degradation and loss of properties during processing and reprocessing. Also, bio-based polymers and blends have less flexibility in polymer design, such as copolymers. In many applications, biopolymers require additives that do not inhibit compostability. To enhance the physical properties and aesthetics of PLA, thus imparting enhanced functionality and the potential for PLA to be considered for a much broader range of applications, additive manufacturers have been working to develop solutions.
Few of the developments include: Biopolymers are often used as a blend of two immiscible polymers, e.g. a stiff, brittle biopolymer (PLA) with an elastic component. These blends need compatibilization to produce a stable polymer blend.
BASF’s Joncryl® ADR Chain Extender makes it possible to manufacture PLA with higher molecular weight, broader molecular weight distribution and higher degree of branching than regular PLA. Such chain-extended PLA has higher melt strength and therefore can be processed with greater stability. They can enable branching PLA which results in higher molecular weight and lower density foams with closed cell structures. The usage of Joncryl® Functional Additives typically requires good compounding and feeding techniques to ensure that the additive is evenly dispersed into the polymer matrix and performs its function, be it chain extension or flow enhancement, effectively. These additives are designed to solve demanding engineering problems and to provide materials enhancements. Therefore, the proper selection of additive for the right applications is as important as their handling and processing.
DuPont has expanded its Biomax® packaging offerings to include renewably sourced Biomax® Thermal 300 heat-stabilizing modifier that allows polylactic acid (PLA) thermoformed packaging to withstand elevated temperatures during transport, storage and use. Its introduction extends the use of PLA to applications beyond chilled foods and beverages. This is the second modifier for PLA to be introduced by DuPont. Biomax® Strong toughening modifier, launched in 2007, improves PLA by enhancing its processibility, durability, impact strength and flexibility. It is petrochemically based. Biomax® Thermal contains 50% renewably sourced content by weight.
Arkema is also targeting PLA as it requires several modifications to become more useful. It’s Biostrength® 280 clear impact modifier is targeted at PLA food-contact applications, adding toughness, ductility and durability to extruded and thermoformed packaging. Biostrength® 900 metal release additive reportedly makes PLA processing more consistent, enhances its flow properties, and widens its processing window.
Masterbatches from Teknor Apex Co. address all of PLA’s main problems: poor impact strength, metal release, and melt strength. A clear impact modifier masterbatch for use with polylactic acid (PLA) bioplastics provides substantial increases in impact strength while sustaining the excellent clarity of the base resin- Terraloy™ 9000-series : masterbatches that use PLA carrier resins to optimize their ease of use. Testing reported by the company showed that at loadings up to 10% in PLA, different 9000-series masterbatches improved Gardner impact strength by ten times or more, increased film pull-force over a range of draw-down ratios, and functioned well as a mold release or provided film/sheet release in extrusion. The pelletized masterbatches disperse more effectively and uniformly in PLA than additives that come in powder form, work well in a wide range of processing equipment, and do not affect the clarity of neat PLA polymer. FDA-accepted for loadings up to 20%, this masterbatch can be used for flexible and thermoformed packaging, extrusion coating, and food service disposables.
Purac has developed a PLA compound with heat stability and impact strength comparable to ABS. This material utilizes stereo-complex technology which is based on it’s unique L-Lactide and D-Lactide monomers for the second generation PLA. The new PLA compound performs at a comparable level to ABS in injection moulding applications. This will enhance the application of PLA in semi-durables and consumer goods. This additive has been developed to better control the polymerization of the material, with the end effect being that processors are said to see smoother processing of the material on their equipment. Under the new process, AkzoNobel’s organic peroxides selectively switch off polymerization catalysts, improving the quality and stability of the PLA polymer. The resulting PLA is more stable in melt processing, has consistent flow properties, and still maintains a positive environmental profile, say the two development partners. The additives are available from Purac.
PolyOne Corp. offers a clear impact modifier for PLA, designated OnCap™ BIO Impact T. The modifier retains PLA’s transparency, it also increases tear resistance, enabling higher production throughput and reducing scrap, without limiting the PLA compound’s food-contact use or biodegradability, when used at prescribed loadings. Its use increases STET impact resistance of PLA while maintaining its transparency. The increased toughness improves tear resistance. This makes the sheet easier to cut during fabrication and simplifies handling and safety by reducing rough edges and uneven cuts. This also makes the sheet fit for final end use, helping improve consumer acceptance. Improved ductility also allows for holes to be punched in trays without tearing or shattering the tray itself.
This results in increased production with less product failure as well as increased food safety. Reduced brittleness decreases the shattering of cups and trays during handling and packing, which lowers scrap rates and increases safety. Attractive, clear parts stand out on the shelf, helping improve consumer acceptance thereby increasing sales revenues and profits.
The increase in use of biodegradable resins offers a new generation of materials, with new properties compared with traditional plastics. The main advantage of these materials is that they can be organically recycled through composting. These new additives enhance the physical properties and aesthetics of PLA, impart enhanced functionality and increase the potential for PLA to be considered for a much broader range of applications.
Source: plastemart.com, 2011-06-14.