Companies are on the march toward goals such as reducing carbon footprint and waste, and bio-based, renewably sourced materials—including modifiers, reinforcements, and fillers used in either conventional or bio-based polymer formulations—can help companies achieve these targets.

Replacing conventional additives and property modifiers with bio-based additives imparts a “green” image for companies that are increasingly interested in promoting their use of bio-based materials. And in carbon footprint calculations, every little bit helps. “What do you have in the ‘bio’ range?” is becoming a more common question from customers, says JP Wiese at Asahi Kasei Plastics.

Availability and use of bio-based materials is partly driven by “[t]he increased scientific ability to harness complex structures produced by natural synthesis (in renewable-based feedstocks); regulatory changes like REACH; and higher end-consumer acceptance of bio-based products,” says Harald Klein, global business director, Green Polymer Additives, at Emery Oleochemicals.

In addition, finding new and more valuable uses for what was previously considered waste is an ongoing movement. “Waste streams” are better called “co-streams,” explains David Grewell, professor at Iowa State University and director of the Center for Bioplastics and Biocomposites, which focuses on developing high-value bio-based products from agricultural and forestry feedstocks.

In plastics, a multitude of materials have been investigated as fillers and reinforcements over the years, and some have overcome challenges and found commercial success. 

Bio-Based Additives

One application for bio-based additives is improving properties such as impact, melt strength, and heat deflection temperature for either conventional or bio-based polymers. In PVC, for example, the percentage of plasticizers and other additives is significant, so replacing non-renewably sourced materials with bio-based ones makes a difference in a product’s carbon footprint. 

Plasticizers, lubricants, antistatics, and dispersing agents from plant sources have been available for some time. Glycerol esters and glycerol monostearate, for example, are widely available from plant sources, such as soybean or sunflower oil, for use as antistats, mold releases, internal lubricants, and dispersants. Bio-based plasticizers include epoxidized soybean oils (ESO) from multiple sources, including Arkema’s Vikoflex ESO.

Paul Keeney, Arkema’s business director for Epoxides, says that the company is developing new bio-plasticizers and notes: “We have been seeing an emerging requirement for newer, safer plasticizers that can replace currently used phthalates while having the acid scavenging properties of ESO. Even in the absence of legislation, we are seeing many companies simply wanting to differentiate themselves from their competitors by increasing the bio-renewable content in their products and being able to promote this in their branding.”

Other available bio-plasticizer types include Segetis bioplasticizers, Dow’s Ecolibrium, DuPont’s Grindsted Soft-n-Safe, and Oxea’s Oxblue DOSX (dioctyl succinate) and Oxblue ATBC (acetyl tributyl citrate).

There’s a move to use more sustainable additives, particularly in Europe, where some changes are being driven by regulations such as REACH. In both Europe and the USA, consumers are showing a desire to have more natural ingredients in their products. 

“Applications like food packaging have traditionally used food-contact-approved additives, but in some cases are moving one step further to using bio-based additives that are also used as ingredients by food manufacturers,” comments Lisa Swain, business development manager at Corbion, which produces bio-based food ingredients, bio-based chemicals (e.g., lactic acid), and food-grade polymer additives.

For example, Corbion sees interest in using its lactates and lactylates (lactic acid derivatives) as catalyst neutralizers in place of metallic stearates or synthetic calcites. Neutralizers based on lactic acid chemistry give less color development in the polymer and improve processing. Corbion’s glycerol ester solutions are used for antistatic, mold release, antifogging, lubrication, dispersion, release, and polymer processing additives.

Non-Food Biomass-Based Additives

Another trend is to produce bio-based additives and materials using biomass rather than food sources, such as sugar. “In 2014, we demonstrated the feasibility of fermentation for the production of lactic acid, lactide, and PLA using second-generation feedstock (plant-based biomass such as bagasse, corn stover, wheat straw, and wood chips),” says Corbion’s Swain. “This next-generation organic acid technology will create a technology platform with the potential to become an integrated part of a biorefinery.”

Corbion has also developed a scalable process for the production of organic acids that recycles almost all auxiliary chemicals, thus requiring fewer input materials and preventing the formation of gypsum, a byproduct in the conventional process. The carbon footprint of lactic acid produced using this new technology is reduced by 20% compared to the conventional process, says Swain. 

Palsgaard, which is also a food ingredient manufacturer, offers plant-based and food-contact approved antifogs and antistats that find use primarily in food-contact applications. The company recently introduced Einar PolyDispers 101, a new plant-based dispersion agent offering better pigment and filler dispersion in color masterbatches than waxes. The dispersing agent is a “non-ionic, surface active component, free from contaminants and low-molecular-weight oils that can adversely affect color critical applications,” says the company. 

The growth of bio-based “drop-in” PET (e.g., for rigid packaging), as well as bio-based polymers like PLA and PHA, can be expected to drive the development of food-grade additives, suggests Emery Oleochemicals’ Klein. Advances in bio-technology have already led to products than provide similar, if not better, performance than their counterparts, he notes. The cost-competitiveness of bio-based additives is improving, and for some, the value of “responsible manufacturing” outweighs the cost, he adds. 

Bio-Based Fillers 

A multitude of bio-based fillers have been investigated. At Ford Motor Co., success stories include the commercial use of cellulose, wheat straw, rice hulls, kenaf, and coconut. Faurecia’s hemp-fiber-filled polybutylene succinate (PBS) compound, NafiLean, was commercialized for parts in a Peugeot model year 2013 car, which was one of the finalists in the Environmental category of the 2015 SPE Automotive Innovation Awards.

A 65% bio-version of the company’s BioMat PBS composite (see the October 2015 Plastics Engineering, p. 13) was commercialized in 2015 through APM (Automotive Performance Materials), a joint venture between Faurecia and a major agricultural cooperative. A 100% bio-version, fully sourced from vegetal residues, is being developed and may be commercial by 2018, says the company.

Cellulose fibers have also found success, with materials such as Weyerhaeuser’s Thrive compound (see last March’s Plastics Engineering) and others. Advantages include dimensional stability and reduced sink marks in thick ribbed parts. 

“There is room for many different types of bio-based fillers, depending on the specific application requirements,” says Asahi Kasei’s Wiese. For example, some bio-based materials have low odor characteristics and can be used in an automotive interior cabin application, but others do not and might be used elsewhere.

A challenge with natural fibers is cost. Another is that the interfaces of many bio-based fillers are not suited for plastics; thus, much research has gone into coupling agents or surface modification to improve mechanical adhesion, although this adds cost, notes Grewell. 

Researchers at Iowa State’s Center for Bioplastics and Biocomposites have investigated many materials, with a recent focus on lignin, which is a large stream of particulate material left from biomass conversion. “No one knows what to do with lignin and make a profit, so we are seeing if we can make it a cost-effective filler,” says Grewell.

“In nature, lignin works as an adhesive binder, and we hope to be able to keep these binding properties. There are some indications that lignin might enhance performance.” Lignin is dark-colored and must be processed at low temperatures. Another problem is that lignin varies depending on its source (e.g., switchgrass or hard or soft wood), and obtaining greater consistency adds cost.

Jute-filled PP compounds are being used commercially already, and have the potential for high growth, says Babu Padmanabhan, founder and managing director at Steer, a compounding extruder manufacturer based in India.

India is one of the largest jute producers in the world, and the government hopes to popularize the fiber’s broader use beyond traditional packaging materials (e.g., burlap), according to Steer’s November 2015 press release. The company’s twin-screw extruders with patented fractional-lobe elements can produce PP compounds with up to 50% jute, paving the way for application development.

The enormous effort going into developing bio-based additives and composites will eventually pay off, predicts Grewell, and commercial use will increase.