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Study offers guidelines to improve the quality of post-consumer recyclate

January 1, 2006

7 Min Read
Study offers guidelines to improve the quality of post-consumer  recyclate

A new study by the California Integrated Waste Management Board (CIWMB) shows that with proper quality guidelines, post-consumer plastics recyclate (PCR) can be processed to meet the specifications for trash bags and rigid containers.

The research, done by the CIWMB in conjunction with Professor Joe Green of California State Univ.-Chico, evaluated the post-consumer plastic processors in California and their respective quality assurance programs. A model quality assurance program for post-consumer plastics was then proposed.

According to Mike Leaon of the CIWMB, two California laws prompted the study: a rigid plastic packaging law and a trash bag law. Both have provisions for using PCR, says Leaon. "One issue with both of these laws is how to use post-consumer plastics and maintain quality," he adds. "This study was in response to that problem."

The best quality procedures from companies in the United States and Europe were used to develop PCR quality control guidelines and testing protocols to ensure high-quality materials. The quality control system is applicable to oft-recycled plastics such as LLDPE, LDPE, MDPE, HDPE, PP, PS, and PET. The emphasis of the study was on the use of PCR in rigid plastic packaging containers (RPPC) and trash bags packaging is exempt from the recycled content mandate but most of the PCR collected originally was food packaging.

The quality of the post-consumer material is a concern, given contamination of the items. Many agricultural films, for example, are covered with dirt and pesticides. Cleaning the PCR is a primary issue.

The CIWMB asked Professor Green, director of the plastics program at CSU-Chico, to develop quality assurance (QA) guidelines for processors. This information can then be provided to processors to improve their QA programs, with the intent to get better quality material. "We''ve not done much in the way of promoting this study so we''d like to increase manufacturers'' awareness that we''ve done it," says Leaon. "It''s a tool they can use for their suppliers (of PCR) to help them get better material."

Edgar Rojas, also with the CIWMB, notes that the main objective was to develop plastic post-consumer guidelines that reprocessors (those firms that make PCR suitable for plastics processing) can use as a model to implement successful QA programs. The study included the QA guidelines and testing protocols, Rojas explains. "We started with some quality control processes, inspections, testing of the received material, testing during processing, evaluation of the most common tests and alternatives, as well as the cost of them," he explains. "We present three case studies about companies with quality problems and what we were able to do to improve the quality of the processed materials. We took samples of the material and tested them on several occasions, then showed the progress these companies made when the testing protocol and the guidelines were implemented."

Leaon adds that the challenge will be to get the reprocessors to see the value of implementing the QA guidelines and do the testing. "We see there''s a definite opportunity for using post-consumer plastics in a higher-value product, if we can assist them in implementing these QA guidelines and help them make a better quality product," he comments.

The study comes at a time when the high cost of virgin plastics is on the minds of every processor. "It seems to me [this study] will have real value," Leaon adds.

To be successful in meeting the recycled content mandate, there is a need to increase collection of materials, and improve their quality, so they can be used in a variety of applications. Currently, the PCR quality guidelines are useful for trash bags, rigid packaging, and plastic lumber; they can be used as a basis for film processors and PCR producers to establish exacting specifications for a particular product. Once these quality specifications have been established between the PCR supplier and the processor, trash bag manufacturers may use PCR with a quality level of 1 (the best grade of PCR). Thicker film and sheet may use PCR with quality grades of 2 or 3, depending on the plastic processors'' specifications. Trash bag manufacturers can use PCR with quality levels of 1, 2 or 3. Rigid packaging manufacturers can use PCE with quality levels of 4 or 5, with level 5 being the lowest quality, notes the study.

Plastic lumber manufacturers can use materials from grades 4 and 5. The PCR quality guidelines encompass all five grades of PCR materials, though different grades will have different testing standards, material specifications, and process control. "The quality assurance program can help PCR manufacturers improve the quality of PCR and provide them with a more consistent product that will ultimately lead to higher profitability and increased PCR usage in California," the report states.

"We see this as the first step-to get the word out that this study has been done," says Leaon. "The harder work is working with processors to get them to see the value in [following these quality guidelines and testing protocols] to help them get higher quality products." - Clare Goldsberry

Case study: Joe''s Plastics Co.

In order to develop guidelines for quality control for post-consumer resins (PCR), the California Integrated Waste Management Board (CIWMB) conducted three case studies. One of those was conducted with Joe''s Plastics Company in City of Industry, CA. The facility has seven extruders with 6.5-inch-diameter extrusion screws that produce approximately 700 lb/hr of PRC per machine.

Input materials consisted of post-consumer and post-industrial plastics, blended in recipes to meet customers'' requirements. The resulting pellets are used for bags, sheet, pipe, or packaging applications, and include LLDPE, HDPE, LDPE, PP, PS, ABS, PC, PC/ABS, PVC, nylon 6/6, nylon 6, EVA, and TPU. The incoming material was sorted, chopped, and densified in an operation separate from the extrusion line, then stored until needed for processing.

The PCR pellets are tested for density, melt index, impact strength, and contamination. Joes Plastic''s existing quality control program included good documentation for production PCR, a contamination notification sheet for incoming materials, and tests for melt index and impact strength. The company has a QA plan that includes testing of the PCR product produced from PP automotive bumpers and PS coat hangers. The PCR material produced for the study was made from approximately 10% post-consumer resin and 90% post-industrial PS and PP.

The main researcher of the project, Dr. Joe Green, noted that contaminants in the incoming materials included white paper labels (less than 1%), rope (less than 1%), metal pieces (less than 1%), broken wood (less than 1%), and plastic tape (less than 1%), which were removed by the operator. Joe''s Plastics then grinds the materials in a grinder that is cleaned between each material change. Each gaylord of chopped plastic is then tested for melt index and density, and checked for contaminants. The gaylord is then moved to the extruder and mixed with other plastics that have similar melt index and density in a recipe at the extruder. This technique, notes the CIWMB report, can be especially helpful for trash bag manufacturers who can blend low-melt-index LLDPE PCR with higher-melt-index LLDPE to produce a PCR with an acceptable melt index. The plastic is added to the extruder in a batch, rather than continuous, process.

Each extruder runs only one type of material: PP on one extruder, PS on another, PE on a third, and so on. The quality of the recycled plastic was moderate, and appeared acceptable for use in the right packaging applications with a PCR quality rating of 5. The CIWMB case study noted that the primary cause of PCR quality problems is the lack of suppliers that can provide recycled plastic of high quality. The other causes of PCR quality problems at Joe''s Plastics could be solved by improved quality control procedures, to include more inspection sheets and less reliance on visual inspection methods.

The contaminants can also be removed, according to the study, by requiring the recycled plastic suppliers to meet specific quality standards. Also, the remaining causes of PCR problems can be reduced or eliminated by improving the quality control procedures and increasing worker training. The researcher of the study determined that Joe''s Plastics would benefit from combining the PCR guidelines with its own quality control system. -Clare Goldsberry

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