Technical Papers Plastics
Applications of PLA to grow with new additive developments

Applications of PLA to grow with new additive developments

Ingeo is made from dextrose (sugar) that is derived from field corn already grown for many industrial & functional end-uses. In North America, corn has been used first because it is the most economically feasible source of plant starches. NatureWorks® is a revolutionary biopolymer made from plants instead of oil and is used in the manufacturing of Ingeo ingredient branded fiber, packaging and consumer goods applications. The cradle-to-factory-gate production process of NatureWorks® biopolymer currently uses 62-68% less fossil fuel resources than the traditional plastic materials such as PET, PS, PP and PE. NatureWorks® biopolymer also further significantly reduces greenhouse gases. Compared with the traditional plastic materials such as PET, PS, PP and PE, NatureWorks® biopolymer reduces greenhouse gas emissions by 80-90%, does not contain persistent, bio-accumulative and toxic chemicals. The second conference on biopolymers was hosted by NatureWorks LLC. Among the highlights were sessions on Successful integration of Ingeo into existing manufacturing facilities, new product developments, blending and additive approaches to tailoring performance. Few of the highlights to Blending and Additive approaches discussed at the conference:
Ningbo, China based Tianan Biologics Co. Ltd. currently has PHBV production capacity of about 2000 tpa. PHBV is a biodegradable, 100% renewable biopolymer made directly by the fermentation of glucose in Ralstonia eutropha bacteria. Compared to PLA, PHBV exhibits excellent heat resistance and low water vapor transmission rates (WVTR), but poor thermal melt stability. Two PHBV/PLA (30/70) and PHBV/ BASF EcoFlex formulations were described showing improved property profiles over the individual biopolymers.
Limitations in impact strength, heat resistance and tensile strength preclude PLA from many high performance engineered durable applications. Maki of RTP Company described a number of compounded biopolymer formulations (32-80% biocontent) as offsets to HIPS, PC/ABS, 30% glass fiber reinforced polypropylene or polyamide composites using PLA alloys or reinforced PLA to achieve notched Izod impact strength ranging from 2-16 ft lb/notch, up to 320°F HDT and 1.6 MM psi flexural modulus. RTP is currently working on several other specialized applications requiring antistatic, custom color, flame retardant, wear resistant, or electrically conductive end-use performance.
Teknor Apex Company�s Anderson described thermoplastic starch (TPS) technology for the modification of PLA biopolymers. TPS can be made by compounding a variety of granulated starches, water and glycerol. TPS/PLA blends can be compounded via patented Teknor Apex technology for improved impact strength, melt strength and metal (mold) release behavior without detriment to biocontent or compostability. Plasticizer level is an effective means of modifying performance with maximum elongation and notched Izod impact strength found at about 36% glycerol, e.g., 200% and 4 ft lbs/in notch, respectively. MB 90000 (non-starch based) series provides improved melt strength or impact strength while maintaining excellent clarity. M20000 (starch based) series provides two levels of further strength improvement, but result in opaque products.
NatureWorks LLC�s Randall described in great detail the formulation and processing conditions for two heat resistant, Ingeo formulations (HHIM and Ingeo 3801X) which were recently developed for injection molded semi-durable applications. Both formulations contain a combination of ca.10% talc, 10% plasticizer/crystallizing accelerant (dioctyl adipate) and 1.0% Takemoto aromatic sulfonate nucleating agent relative to the Ingeo polymer. Heat resistance is gained by the in-situ crystallization of the PLA component. The Ingeo 3801X formulation also contains about 10% Arkema Biostrength 150 proprietary impact modifier. Injection molding processing conditions are critical to achieving a balance of both heat resistance and impact toughness. (Notched Izod impact strength was found to be inversely proportional to mold temperature.) Neither of these two products is compostable nor approved for food contact. To support the durability of Ingeo products, the effect of ageing on molecular weight stability for several different Ingeo products under elevated temperature and humidity were presented along with molecular weight data recently obtained for retained samples stored for 8 to 17 years under ambient office conditions. Estimated useful product life for unmodified grades were >10 years for amorphous high % D Ingeo polymers and >20 years for crystallized low % D Ingeo fibers. Recommendations for DSC and accelerated aging test protocols were also presented.
PolyONE�s Avakian presented information on the new reSound Biopolymer line which contains a minimum 30 wt% Ingeo, PHB, PHBV, etc. for applications requiring improved sustainability and higher engineered performance. PolyONE was able to improve key HDT to 120°C and notched Izod impact strength up to 14 ft lbs/in notch without requiring any special PLA grade. Performance was shown to be independent of D-lactic acid content as evidenced by equivalent performance for blends made with Ingeo resin grades, e.g., 4032D, 4042D, 4060D. The reSound™1100 series is targeted at polypropylene and ABS resins, while the reSound1200 series emulates PC/ABS blends having higher performance characteristics. Target markets for reSound biopolymers include automotive interiors, electronic enclosures and high heat packaging. Comprehensive additional data was presented supporting the durability of these formulations under conditions of high humidity and elevated temperature while not supporting fungal growth and QUV and Xenon accelerated UV exposure.
Wolf from Enercon Industries Corp focused on strategies used to increase adhesion of UV Flexo inks to PLA surfaces. UV Flexo inks are considered a more sustainable printing technology with 100% solids ink systems containing monomers, oligomers and photo-initiators for high graphic brilliance. Optimization of UV flexo ink anchoring to PLA surface requires surface modification by corona, flame or atmospheric plasma for roughening and functionalizing effects. Corona treatment of PLA surfaces was found to provide the best adhesion for the polyester acrylate biologomer and fatty acid modified polyester formulations studied.
Dr. Sokolowski from BASF focused on the applications of Joncryl-ADR family of multifunctional chain extenders. The primary reactive functionality present in these oligomeric chain extenders is the epoxy groups, which react preferentially with carboxylic acid end-groups of PLA to generate esters of increased weight-average molecular weight and viscosity. Several grades of Joncryl-ADR are available with different glass transition temperature, molecular weight, and epoxy concentration. The melt strength of PLA can be increased to that of polystyrene upon adding <1 wt% Joncryl-ADR, while low Joncryl-ADR loadings have also been found to provide regular shape and steady and continuous blown PLA film at increased line speeds, while maintaining film clarity. A further application of Joncryl-ADR is in the compatibilization of immiscible and compostable polymer blends, such as polyhydroxyalkanoates and BASF Ecoflex®. The low loadings of Joncryl-ADR required to bring about improved rheological and mechanical properties of PLA does not negatively impact the compostability of PLA per ASTM D6400. Sokolowski recommended zinc stearate as a catalyst for PLA + Joncryl-ADR reactions, and noted that ageing of PLA pellets was better after reacting with their epoxy.
Hiei from Takemoto Oil & Fat Co., Ltd, Japan focused on efforts within Takemoto targeted to the identification of nucleants that can increase the semi-durables market penetration of PLA. The technical objective for Takemoto was to reduce cycle time in injection molding process, and thus a nucleant was sought where the onset of crystallization occurred at the highest possible temperature. Several aromatic sulfonate nucleants, of unspecified structure, were screened using different Ingeo resins. At 1 wt% loading in Ingeo 3251D resin, Takemoto�s LAK-301 nucleant was found to reduce injection molding cycle time to <30 seconds at a peak crystallization temperature of 115.2°C. Hiei noted that a patent pending for LAK-301 nucleant in Japan, USA, Europe, Asia and Australia.
Arkema�s Dr. Cygan focused on the applications of Arkema Biostrength® acrylic additives for improving the impact strength, melt strength, and compatibilization of PLA. Biostrength 280 (introduced at ITR 2010) impact modifier at 4 wt% loading provides high impact and low haze, while Biostrength 150 was developed to provide high impact for opaque applications, durables and blends. Biostrength 700 is a transparent melt strength additive for PLA that improves processability, while meeting FDA standards for food contact certification. It has also been found in improve PLA compatbilization with polyolefins. Biostrength 900 additive was developed to improve PLA metal release without impacting clarity. Dr. Cygan noted as a commercial example, the PLEXIGLAS® RNew family, which are PLA/PMMA blends.
Sukano Products Ltd�s Mr. Ganz provided a thorough review of commercially available Sukano additives and masterbatches for film extrusion applications made from PLA. New BIOLOY biobased polymer alloys are ready to use compounded alloys made from an array of compostable biopolymers, and designed for injection molding applications. These products contain impact modifiers and processing aids to make them suitable for easy processing and contain fillers to obtain the desired mechanical properties.
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