Materials Additives & Blends Take PLA Upscale

The second conference on biopolymers hosted by NatureWorks LLC, Minnetonka, Minn., this April in Dallas, testified to the burgeoning interest in this new field of plastics. Attendance was up more than 50% from the first conference in 2008. Over 350 attended from 30 countries, plus 35 co-exhibitors, twice as many as before. Among the highlights were sessions on new product developments based on the company’s Ingeo polylactic acid (PLA), as well as on additives and blending approaches to tailoring and enhancing PLA processing and performance, elevating it from mainly disposable uses into the semi-durable realm.

 

NEW ADDITIVES ENHANCE PLA

Additive manufacturers have been working feverishly to develop solutions to some chronic limitations of PLA and other biopolymers. These 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.

BASF Corp., Florham Park, N.J. presented the latest information on its Joncryl ADR oligomeric chain extenders, which act as processing aids and property enhancers for biopolymers in blown film, sheet, and blends. These chain extenders comprise three classes of solid or liquid monomers—styrenics, methacrylates, and glycidyl acrylates (an epoxy-functional acrylate). Joncryl ADR rebuilds the molecular weight of PLA lost to hydrolytic degradation during melt compounding. According to business development manager Alex Sololowski, Joncryl ADR additives maximize chain extension without crosslinking or gel formation. The new series also includes grades with FDA approval for PLA foam and sheet.

They can be used at low loadings (0.4% to 0.5%) to increase PLA’s molecular weight by 25% to 200%. Benefits reportedly include improved melt strength and foamability, better processability at elevated regrind/recycle levels, and higher throughput. In addition, the increase in molecular weight has been shown to boost mechanical properties, even under poor predrying conditions, and to lead to a more robust product that is less susceptible to process variation. Specific grades have been shown to be particularly effective in certain applications:

• Joncryl ADR 4368 and 4370 maximize melt viscosity through branching where high melt strength is needed for steady parisons, non-sagging profiles, and closed-cell, low-density foams.
• Joncryl ADR 4300 and 4385 increase melt viscosity through moderate branching for higher elasticity in deep-draw thermoforming and orientation processes.
• ADR 4380 raises melt viscosity through linear extension for resistance to shear-rate variations in injection molding.
   

Arkema Inc., Philadelphia (arkema-inc.com), highlighted a new addition to the company’s Biostrength high-molecular-weight acrylic additives for PLA. Biostrength B280 transparent impact modifier is said to be particularly well suited to toughening sheet for reduced scrap and increased line speeds. In experiments with 15-mil sheet, B280 was shown to impart less haze with the same level of toughening as two competitive modifiers.

Meanwhile, the company’s Biostrength 700 transparent melt-strength enhancer has been shown to also improve compatibilization of PLA with polyolefins, as in a 50/50 LDPE blend.

Sukano Polymers Corp., Duncan, S.C., presented some of its latest additive masterbatches for PLA. According to business development manager Daniel Ganz, the biggest area of improvement has been in rectifying the low heat and impact resistance of PLA and other biopolymers. Work is also under way to improve barrier properties and reduce yellowness/haze and cost.

• Sukano’s PLA dc S511, a transparent slip/antiblock masterbatch for PLA reduces the coefficient of friction of film and sheet. Deep-draw thermoformed parts demold and denest much easier and films have much less tendency to stick during unwinding.
• PLA mr S533 is a heat-stable mold-release and processing-aid masterbatch that is said to improve injection mold filling and demolding of parts. It provides clear, neutrally-colored parts, good printability, compostability, and food-contact compliance.
• PLA na S516 and PLA na S516-IceClear are transparent nucleator masterbatches that control crystallization during processing for faster cycles and improved mechanical and optical properties. It also reportedly enhances heat resistance of PLA.
• PLA uv S547 UV masterbatch is said to protect light-sensitive goods in clear PLA packages.
• PLA a S546 transparent antistatic masterbatch helps keep dust off film, sheet, and molded parts.
• PLA im S550 and im S555 are transparent impact modifiers. Even thermoformed cups or trays with sharp edges reportedly gain excellent impact resistance.

 

Takemoto Oil & Fat Co., Ltd. of Japan  discussed a new nucleator that can advance the use of PLA in semi-durable applications with high-temperature requirements. According to technical sales manager Michyia Hiei, three of these novel aromatic/sulfonate nucleating agents—LAK-101, 201, and 301—surpass talc or clay in shortening cycle times for Ingeo 3001D injection-grade PLA at loadings of 1% to 2%.

Greg Anderson, technical manager for bioplastics at Teknor Apex Co., Pawtucket, R.I.  reported on the company’s new line of Terraloy masterbatches or compounds based on thermoplastic starch (TPS), which can be custom blended with PLA to achieve a wide array of properties. For example, addition of 4% to 8% of Terraloy MB-90001A, a water-clear melt-strength additive, has been shown to increase PLA’s pull force in extrusion by three to five times. Addition of 10% to 20% of Terraloy MB-20015A, an opaque TPS/PLA blend, can increase the pull force by four to six times. And addition of 10% to 20% Terraloy MB-29013A opaque PLA alloy can increase the pull force by seven to nine times.

For toughening PLA, Teknor offers Terraloy MB-90000A clear masterbatch; MB-28008A opaque TPS masterbatch with higher toughening; and MB-29014A opaque masterbatch with maximum toughening. The latter can boost Gardner impact by 10 to 15 times at 125-mil thickness. All these reportedly provide ductile failure.

To foster development of biopolymers in injection molding, NatureWorks has borrowed a page from the computer industry and is now providing “open-source” access to full details of formulation and compounding procedure for its high-impact Ingeo 3801X and high-heat Ingeo HHIM670-82-01 compounds.

 

BLENDS TAILOR PLA PERFORMANCE

Arkema discussed its transparent PMMA/PLA blends, marketed as Plexiglas RNew. They contain 20% carbon from renewable resources and reportedly have optics, mechanical strength, scratch resistance, and UV stability similar to PMMA.

Sukano unveiled its new Bioloy PLA compounds and blends for injection molding. They are said to provide stiffness, impact, and gloss similar to general-purpose polymers. They reportedly offer easy processing, better impact strength than neat PLA, and shrinkage and cycle time similar to PP and nylon. They can provide glossy surfaces and are offered in precolored opaque grades.

• Bioloy 002 is a compostable, semi-crystalline alloy containing 35% biobased carbon. It boasts excellent mechanical properties and improved HDT of 65 C/149 F. It is targeted for caps and closures, E/E housings, and sporting goods.
• Bioloy 003 is a compostable, semi-crystalline alloy with 50% biobased carbon. It reportedly withstands short-term exposure above 100 C/212 F.
• Bioloy 004 is a compostable amorphous blend containing 97% biobased carbon. This clear, cost-effective formulation is said to provide excellent mechanical properties at up to 60 C/140 F. It is aimed at consumer products and durable goods.
• Bioloy 005 is a compostable amorphous alloy containing 70% biobased carbon. It is said to provide impact and stiffness similar to g-p ABS. It is aimed at cosmetics and personal-care packaging, housewares, toys, and decorative goods.

 

RTP Co., Winona, Minn., discussed its new engineered compounds based on Ingeo PLA. These include high-impact PLA/ABS (RTP 2099 X 121216 G) with 80% bio-content and notched Izod impact of 2.5 ft-lb/in., competitive with HIPS. A high-impact PLA/PC alloy (RTP 2099 X 121235 D) has 32% bio-content and notched Izod of 16.5 ft lb/in., competitive with PC/ABS. And 30% glass-filled, nucleated PLA (RTP 2099 X 124752B) with 70% bio-content reportedly bridges the gap between a glass-filled PP and glass-filled nylon 6. It boasts a flex modulus of 1.6 million psi, tensile strength of 15,700 psi, and HDT @ 66 psi of 320 F. It also has excellent long-term heat and humidity resistance.

Blends of a bio-polyester copolymer, PHBV (polyhydroxy butyrate valerate), produced by microorganisms from natural sugars, can broaden the applicability of other biopolymers such as PLA, according to James Lunt, v.p. of sales and marketing for Tianan Biologic Co., Ltd., Wayzata, Minn. Based in China, Tianan is the world’s largest producer of PHBV, marketed under the Enmat trade name. Recent work shows that PHBV/PLA blends offer better heat resistance than PLA alone; wider processing window than PHBV; and a broader spectrum of properties than either one can provide. These blends show promise to move PLA into durables with high renewable content.