A Renderable Solution for Polyethylene Bags

By Annel K. Greene, PhD, Professor and Center Director
Clemson University Animal Co-Products Research and Education Center


Members of the Fats and Proteins Research Foundation (FPRF) challenged Clemson University’s Animal Co-Products Research and Education Center (ACREC) researchers to find a solution for a plastic contamination problem and Dr. R. Andrew Hurley fulfilled that challenge. Several types of polymers are accidental contaminants that can end up in raw materials. Polyethylene film is particularly difficult to process as it can wrap around augers and, if sufficient film is present to bind the system, can cause damage to gearboxes. Upon thermal processing, polyethylene melts and remains with the fat where it creates problems with pumps and general downgrading of the value of the fat. Plastic particles of polyethylene and other polymers are detrimental in finished protein meals, especially for pet food-grade materials. Often brightly colored, these plastics are a source of concern to rendered product customers.

Hurley, assistant professor in the Department of Food, Nutrition, and Packaging Sciences and a member of the ACREC research team, investigated over 100 commercially available plastic polymers as a replacement for polyethylene. In the early stages of the project simply using a frying pan, gas grill, and lard, Hurley screened polymers and determined their fate during a high temperature cooking process similar to rendering. From his early trials, he was able to narrow the choices and eventually select a commercially available polymer for preliminary liner formation and testing. The biodegradable thermoplastic polymer is made from corn and can be melt-processed for a variety of uses.

Hurley tested the liners using a modified ASTM International Standard D4169 distribution test in which a 0.88 millimeter (mil) liner was placed into a 44 gallon Rubbermaid Brute waste bin. The liners passed both an incline impact and random vibration test when filled with water and secured with a lid. Hurley also conducted a full field test at a commercial rendering company batch processing facility in which over 900 three gallon liners (0.88 mil thick) made from the biodegradable polymer were mixed with raw materials. After processing, the products were tested and results were negative for polychlorinated biphenyls and pesticides. Measurement of the polyethylene content of the fat produced during the test was not different from the control. After the crax were processed through a hammermill and the resultant meal inspected, no plastic liner remnants were detectable even under microscope analysis.

After the initial test, Hurley had 24,000 liners of the biodegradable polymer made in two thicknesses – 0.88 and 1.5 mils. These liners were distributed to store clients of four continuous rendering facilities in four different geographic locations in the United States. In all, more than 100 store locations used the liners. The route drivers were instructed to collect both the liners and contents. The study was conducted over four weeks. The materials were rendered and samples of finished fat were collected at all four rendering plants and tested for polyethylene content at a commercial laboratory. Employees of the four rendering plants visually inspected samples of meals and no bag residue could be found.

A survey of route drivers, client store managers, and rendering plant managers was conducted related to the integrity and stability of the liners during the test. Ten route drivers responded to the survey. All reported the biodegradable bags to perform better than polyethylene bags.

Ninety-nine client store managers participated in the survey. Of those, 42 stores used the 0.88 mil liners and 57 stores used the 1.5 mil liners. The majority of responses were positive indicating improved performance of the biodegradable bag over conventional polyethylene bags. Survey questions asked store managers about cleanliness of barrels after using bags, bag structural integrity, and preference. The vast majority of store clients preferred the biodegradable bags. In addition, stores reported less water usage and less labor time spent on cleaning barrels by use of the improved biodegradable and renderable bags. Several stores reported reduced odor from the new liners as well.

Rendering plant managers reported no processing problems associated with use of the liners as determined by examination of raw material conveyors, raw material conveyor pumps, material grinders, production fat screens or filters, production fat centrifuges, fat work or finish storage tanks, production fat pipes or valves, or Rotex screens. Additionally, the survey asked whether there was any visual evidence of the biodegradable polymer in crax or meal and asked the managers to report any negative or positive observations. Not a single rendering plant manager reported any issues or problems related to processing the 0.88 and 1.5 mil liners. The “poly count” test for polyethylene conducted at an independent testing laboratory revealed that purposely adding 6,000 of the biodegradable, corn-based liners to the rendering cooker did not increase poly count. In fact, one processing plant even reported a greater than 50 percent reduction in poly count.

Through this project, Hurley has found a biodegradable, renderable, safe polymer that can be used as a liner that does not clog, plug, increase poly count, or contaminate meal. The new liners are overwhelmingly preferred by drivers, client store managers, and rendering plant managers. The biodegradable liners reduce water and labor usage and perhaps even odor.

In addition to funding from FPRF, two rendering companies supported this project through technical assistance and the purchase of liners.

Hurley is currently working on a second project to develop gloves from the biodegradable polymer for use in meat and poultry processing plants and is looking for processing companies willing to participate in the project using the gloves. Gloves frequently become incorporated in raw materials and use of the biodegradable material that can be rendered will improve animal by-product quality. The biodegradable material is already approved by the Food and Drug Administration for food contact. Hurley is working with a glove manufacturer to develop different styles of gloves from the biodegradable material.

Reduction of polyethylene in the raw material stream will greatly improve finished animal by-products. Use of a corn-based polymer that is fully degradable to a starch product will be of great benefit to the industry. Hurley has successfully met the challenge posed to him by the rendering industry.


October 2013 RENDER | back