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Lignin-reinforced PLA Imparts Antioxidant Effect with Controlled Biodegradability

KraussMaffei Extrusion has tied up with a Polish partner to develop a bio-based injection molding compound with enhanced mechanical properties


At a Glance

·       Focus on valorization of hydrolysis lignin, which is a byproduct of bioethanol production

·       Lignin waste product is converted into a value-added filler that can potentially be employed in packaging and agricultural mulch film

·       KraussMaffei compounding technology spearheads ability to integrate up to 30% lignin content into the PLA matrix

 

KraussMaffei Extrusion has tied up with Synergy Horizon Poland Sp. z o.o. to develop a process for producing a 100% bio-based reinforced thermoplastic: lignin-reinforced polylactic acid (PLA). "With our compounding expertise and our project partner's unique knowledge of lignin preparation, we have succeeded in incorporating up to 30% lignin into the PLA matrix and producing a compound with natural antioxidant capacity/activity, enhanced mechanical properties, and controlled biodegradability," says Lars Darnedde from process engineering development and project manager at KraussMaffei Extrusion.

With a focus on hydrolysis lignin valorization, the Synergy Horizon group of companies transforms lignin, a biopolymer that is often discarded as a by-product of bioethanol production, into valuable products for various applications. The company’s competencies entail lignin purification, its chemical modification and functionalization. They offer lignin-derived products for various applications, such as oil and gas extraction, battery production, water treatment, and animal feed.

 

From waste product to functional filler

Synergy Horizon Poland has also been developing a process at its Polish site in Poznan for the production of free-flowing lignin powder that can be metered into the extruder as a filler. Lignin is a 100% natural substance that is second only to cellulose as the most abundant organic material on Earth. Lignin can be extracted from lignocellulosic biomass by various methods. One of these methods is the hydrolysis of biomass for bioethanol production, which generates hydrolysis lignin as a byproduct. Hydrolysis lignins have unique properties that make them stand out from other types of lignin.

Around 50 million tonnes of lignin, including hydrolysis lignin, are produced annually worldwide as a waste product from wood processing by the paper and bioethanol industries, 98% of which is incinerated. Various research projects have already focused on the valuable renewable bioresource, but its use as a filler in a biopolymer matrix is so far unique. "However, processing hydrolysis lignin is not an easy task," notes Alexander Gonchar, head of research and development at Synergy Horizon. “Our intensive development work [has enabled us to] now successfully operate a commercial production line for manufacturing lignin powder.”


Image Courtesy of KraussMaffei Extrusion

 

Up to 30% lignin content

KraussMaffei has demonstrated the incorporation of the natural raw material into the PLA matrix at its newly established technical center in Laatzen, Germany. Both the laboratory extruder, a ZE Blue Power 28, and the small ZE Blue Power 42 production compounder succeeded in incorporating up to 30% lignin. "We have specially adapted the screw configuration to the lignin with heavy-sensitive mixing elements, operate at a low temperature of 160°C maximum, and use both a 6 D-long filling zone and side degassing," notes Lars Darnedde with regards to the process configuration. The ZE BluePower generation with its optimum Da/di of 1.65 offers all these possibilities "out of the box" and is thus perfectly suited for processing these shear- and temperature-sensitive polymers.

Compared to pure PLA, lignin reinforcement enables flexural and tensile modulus to be increased by around 30%. Potential applications include packaging applications where the material needs to be stiff enough to hold its shape under load.

Another advantage is that lignin adds sufficient antioxidant capacity that can help particularly in food packaging application to prevent oxidation of the food and maintain its quality and safety by inhibiting the radical oxidation and preventing the formation of off-flavors, odors, or toxic compounds. Moreover, the lignin biocompound is odorless unlike other type of lignin, which makes it more suitable for food packaging

A novel bio-compound that exhibits antioxidant properties could also be applied to biodegradable plastics for agricultural purposes, such as mulch films, to protect them from oxidative degradation. Unlike pure PLA, which has limited biodegradability due to its dependence on specific enzymes and industrial conditions, PLA bio-compounds containing lignin exhibit enhanced biodegradation properties with biodegradation rate more than 90% in 99 days.

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