Cellulose derived nanocrystals plus PLA equal bioplastic nanocomposites

October 13, 2011

The first nanomaterial from an entirely renewable resource—that advance, nanocrystalline cellulose (NCC), was among many material developments announced during the recent 2011 Biopolymers Symposium , showcasing how R&D dollars are chasing the bioplastic/renewable polymer space, which may be small in size relative to traditional plastics but is growing rapidly in applications.

Joining NCC, which is described as a highly ordered crystalline cellulose that can be used to fortify bioplastics for a 100% biobased nanocomposite, were biobased aliphatic thermoplastic urethanes (TPU), compostable adhesives, stereo polylactic acid (PLA) blends, 100% biobased polyesters, food-contact film grades of polyhydroxyalkanoate (PHA), and more.

Nanocomposites, naturally

Wadood Hamad introduced NCC to the symposium on behalf of CelluForce, noting that while cellulose is abundant in nature, it doesn't exist on its own, and isolating has heretofore been a major hurdle. Research into the nanocrystals goes at least back to 1951, according to Hamad, when the first colloidal suspensions were made, but leaps in technology and production have been made over the last five years.

CelluForce nanocrystals
 Scanning electron microscope images of PLA extruded with nanocrystals.

In 2006, a company called FPInnovations set up a pilot plant, with a daily output of 2 kg. In 2010, CelluForce and Domtar set up a joint venture with FPInnovations, and are working on a facility in Windsor, ON that is planned to have 1 ton/day of production when it starts up in January 2012.

CelluForce's technology involves removing lignin and putting it through a selective acid hydrolysis to liberate highly ordered crystalline cellulose, with a yield of 95% crystals. The NCC's measure 5 to 15 nanometers wide and 100-150 nanometers long. Essentially a charged polymer, the nanocrystals have an active surface that can be modified and can self assemble orienting into pseudo plans in suspension. Also unique is the chiral nematic structure they impart to surfaces, or, as Hamad described it "color without dye." Like a butterfly, the crystals have different colors from different angles.

Hamad called NCC a "high performance reinforcement in polymer composites," comparing the cellulose-derived nanoparticles to carbon nanotubes, carbon fibers, and high-end composite fibers like Kevlar and Aramid. "NCC can be used and basically compete on an equal footing," Hamad said, noting their high strength and low density. In early testing, a 5% loading of NCC in PLA increased stiffness by 10 times, while also improving its barrier.

The technology is reminiscent of one promoted by PolyNew during the February 2009 Society of Plastics Engineers ' Global Plastics Environmental Conference. PolyNew discussed its proprietary technology for the surface functionalization of cellulose fibers, which resulted in hydrophobic cellulosic nanowhiskers . Those cellulosic nanowhiskers were added to PLA to create sheet stock that was suitable for thermoformed frozen food trays.

Next generation biobased TPU

Merquinsa's Dennis Lauzon highlighted his company's work towards an aliphatic TPU: a new low-color technology that would be "water white" versus the slight yellow tint seen in current biobased TPUs, which use a renewable resource for the polyol segment. Beyond the color, Lauzon said the development promises new functionalities and the opportunity for cost parity with petroleum-based

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