NU 2015-107

Inventors 

John Torkelson*

Krishnan Iyer

Short Description

A method using natural antioxidant-rich agro-wastes as a low cost green processing and long-term thermal stabilizers for polymers with performance comparable or superior to commercial antioxidants.

Background

Commodity plastics such as polyethylene (PE) and polypropylene (PP) are used in numerous applications ranging from toys, containers, and food packaging to prosthetics. The processing and recycling of such polyolefins involve conventional melt processing operations which can promote oxidative degration. Long-term environmental weathering can further amplify material degradation and deteriorate mechanical performance and optical properties of recycled plastics. Antioxidants are commonly added to polyolefins during processing to improve high-temperature processability, long-term weathering resistance, and recyclability. However, the effectiveness of thermal stabilizers or antioxidants in stabilizing polymers depends on many factors including solubility, dispersion, ability to stabilize different polymer matrices, evaporation or volatilization during processing, conditions of use, and recycling. Unfortuantely, stabilization of polyolefins with synthetic antioxidants has posed potential health issues and environmental challenges. In particular, plastics used for food packaging have come under scrutiny over concern for food contamination and as a source of unknown cytotoxicity.

Abstract

With concern over the use of synthetic antioxidants in plastics and their unknown cytotoxic effects, Northwestern researchers have looked to greener, natural alternatives as a possible source for antioxidant additives. They examined organic waste materials from sustainable agricultural sources (e.g. grape pomace waste, turmeric shavings and waste, coffee grounds, and orange peels) and their respective characteristics with regard to polyolefin processing and long-term thermal stabilizing characteristics. Rich in antioxidants, biocidal phytochemicals and antibacterial agents themselves, these natural fillers have the potential to exhibit similar desired properties in polymers. The researchers found that the incorporation of 0.1-20 wt% natural fillers using any of a number of solid-state processes (e.g., ball milling, pan milling, bath intensive mixing in the solid state, solid-state shear pulverization, etc.) or melt processes (e.g., twin-screw extrusion) achieves sufficiently homogenous filler dispersion. The same result is also achieved with a four-step process using rotational molding: (1) dry-mixing; (2) melt compounding; (3) palletization; and (4) solid-state grinding. Compared to polyolefins with synthetic additives, these natural composites possessed enhanced thermo-oxidative stability as well as antifouling properties and/or antibacterial activity which could have useful applications for antifouling membranes and coatings. Such articles may also be particularly useful in products for the clinical or hospital setting and for baby care products.

Applications

• Antifouling of membranes, filters, coatings

Advantages

• Increase long-term stability of polymers
• Improves antioxidant, antifouling and antibacterial properties of polymers
• Features natural, green and sustainable additive
• Exhibits comparable or superiror performance to synthetic antioxidants

Publications

Iyer K, Zhang L and Torkelson J (2016) Direct Use of Natural Antioxidant-rich Agro-wastes as Thermal Stabilizer for Polymer: Processing and Recycling.  ACS Sustainable Chemistry & Engineering. 4: 881-889.

IP Status

US Issued Patent No. 9,938,397.  A PCT application has been filed.