I. INTRODUCTION

Manual Objectives and How to Use the Guide

This summary of Best Practices documents HDPE recycling industry methodology and recommendations for the efficient techniques and improved safety for each of the major recycling processing steps. It is intended to be a guideline for operators of recycling processes on various topics without infringing on any organization’s proprietary process technology or techniques.

Each section highlights the “Issue” associated with the specific process step and the related “Best Practices” that improve efficiency, reduce cost, improve quality or enhance safety of the particular operation.

Any other interested parties who would like to or need to know more about the recycling process for HDPE may also find this guide of value in understanding the process and the controls required to enhance the production of a quality product in an economical manner.

HDPE Plastic Overview

One of the most familiar types of plastic packaging found in American households is made from a plastic called high-density polyethylene or “HDPE” for short. HDPE is one of the most versatile plastic resins used in the packaging industry, and is used in bottle, film and injection-molded packaging applications. HDPE plastics offer a wide range of desirable properties and characteristics for packaging applications such as toughness, low cost and good barrier properties (See Appendix A for more details).

LEGAL DISCLAIMER

The HDPE Best Practices Guide has been prepared to provide some helpful ideas for facilities interested in recycling HDPE from discarded bottles. Facilities developing the recycling process and all entities involved in the chain of collection, processing, distribution and sale of recycled products have an independent obligation to ascertain that their actions and practices meet all relevant laws and represent sound practices for their particular operations. This guidance manual is mostly general in nature, and sometimes specific with examples or specific details, but leaves dealing with product and site-specific circumstances to the individual entities developing the recycling operations. Facilities may vary their approach with respect to particular operations, products or locations based on specific factual circumstances, the practicality and effectiveness of particular actions and economic and technological feasibility.

This guidance manual is not designed or intended to define or create legal rights or obligations. Recycling facilities are, of course, expected to comply with federal, state, and local laws and regulations, and should consult with legal counsel concerning such matters.

This guidance document briefly summarizes some of safety issues and guidelines for consideration when operating an HDPE recycling facility. It is not intended to define or create legal rights or obligations related to these safety issues and guidelines, or to provide specific legal or technical advice. The person that uses this document has an independent obligation to ascertain that their actions and practices represent sound safety practices.

The contributors, developers and publishers of this guidance manual do not make any warranty or representation, either express or implied, with respect to the accuracy or completeness of the information contained in this manual; nor do the contributors, developers or publishers of this manual assume any liability of any kind whatsoever resulting from the use of or reliance upon any information, procedures, conclusion, or opinion contained herein.

HDPE Bottle Applications

HDPE is especially desirable in blow-molded bottle applications where it provides excellent physical and chemical strength properties, ease of processing and forming, resistance to breakage, and favorable costs. These properties make HDPE one of the two major resin types used for the production of plastic bottles. The other major resin for plastic bottles is PET. Each of these materials is used to produce approximately 47% of the plastic bottles sold in the United States.

HDPE bottles are used to package a range of consumer products including milk, juice, spring water, vinegar, dish and laundry detergent household chemicals such as floor cleaners, ammonia, bleach, drain cleaners, motor oil and other automotive products; and, health and personal care products such as rubbing alcohol, peroxide, shampoos, and conditioners.

Other Packaging Applications

Because of its wide range of properties, HDPE is also used in a number of non-bottle packaging applications such as injection molded margarine, yogurt and other non-bottle dairy product containers; and, film products such as grocery, produce and garbage bags, deli wrap, and snack-food wrappers.

HPDE Bottle Recycling

HDPE bottles are normally collected via curbside collection programs or community drop-off containers in conjunction with other plastics and other packaging materials. Most community collection programs only target the collection of plastic bottles and therefore this manual will focus only on the best practices associated with the recycling of plastic bottles. If the plastic bottles are collected commingled with other materials they commonly are delivered to a Materials Recovery Facility (MRF) where they are separated from the other materials either manually or via an automated system. The MRF may sort HDPE bottles from other plastic bottles or sell a mixed plastic bottle bale to a Plastics Recovery Facility (PRF) for sorting into the generic resin types. Once the bottles are separated by resin type, they are transferred to a plastics recycler who will reclaim the bottles through a series of steps that lead to the production of a clean plastic flake or a pellet that is marketed as a raw material for producing a broad spectrum of HDPE based products.

II. HDPE BOTTLE Recycling – An Overview

Reclamation Processes

Baled HDPE bottles from MRFs or PRFs are sent to reclaimers that process post-consumer HDPE plastic into a form that can be used by converters or end-users -- either as clean regrind (flake) or in pellet form. At a reclamation facility incoming baled bottles pass through a series of sorting and cleaning stages to separate HDPE from other materials that may be contained on the bottle or from contaminants that might be present.

While each reclaimer has a unique configuration or combination of processing stages to produce a clean flake or pellet, a “typical” reclaimer includes the following processing steps:

Debaling

Incoming HDPE bottle bales are broken apart either manually or automatically, to produce a stream of individual bottles for sorting.

Screening

After debaling, most reclaimers pass bottles through a trommel (rotating) screen or other type of screening device to remove dirt, stones and rocks, metals, or other physical contaminants that might be present.

Sorting

Bottles then pass via conveyor through manual or automated sorting systems to remove non-bottle HDPE plastics, non-HDPE plastic bottles, and other identifiable contaminants (glass or metal containers, film plastics, rocks etc.) to yield a clean stream of HDPE bottles for further processing. Very often, conveyors are equipped with magnets for ferrous metal removal.

Granulating

Prior to granulating, some reclaimers will first shred HDPE bottles. Shredding of the plastic bottles into strips also assists in removing large metal contaminants that might be trapped inside HDPE bottles before grinding, which could cause damage to the grinder, and provides a more uniform feed stream for, granulating equipment. The granulating process loosens paper and plastic labels, and frees other contaminants present on or in the bottles. The inclusion of a shredding step often results in the production of a more uniform particle size / flake by the granulator.

Washing and Float/Sink Separation

Cleaning systems generally consist of a combination of washing, float/sink separation, and/or hydrocycloning stages. Configuration varies between reclaimers. These systems are designed to remove non-HDPE plastic resins, dirt, glass, or metals that might be present; liberate product residues, labels and adhesives; and, generally clean the material to a stage where it can be melt processed to a finished pellet.

· Washing: The washing stage is designed to remove remaining labels, adhesive, or product residues on the HDPE flakes. Each reprocessor has their own unique configuration of washing and rinse stages that will meet the quality requirements of their specific end-use application for recycled HDPE. Some reclaimers use water-based systems, while others use water and chemical based systems employing detergents, emulsifiers (to remove petrochemical residues) or anti-foaming agents (to reduce foaming from detergent residues) to clean the regrind and liberate the remaining labels for subsequent removal.

· Float/Sink Separation: Float/sink separation uses water to separate materials based on their density or specific gravity. Material with a specific gravity greater than water will sink. Materials with a specific gravity less than water will float. HDPE has a specific gravity less than water and will float. Many contaminants to HDPE recycling, such as stones, dirt, metals, and non-HDPE plastics, such as PET (#1), and PVC (#3), are heavier than water and will sink.

Float/sink separation tanks are usually equipped with a series of paddle wheels that agitate and help loosen contaminants from the HDPE flakes. Some float/sink systems use a mild detergent to begin the cleaning process, while others do not. A paddle wheel is frequently used to remove the floating HDPE flake to a dewatering or spin-drying station to remove dirty wash water. Float sink separation can occur before or after washing, or both, depending on the specific system.

· Wash Water Separation

After washing, the HDPE flakes are separated from the dirty wash water by filtering, or spin-drying. The dewatered flake is usually then rinsed and dewatered again, to remove adhesives or contaminants that may have resettled on the flakes.

The dirty wash water is normally filtered and blended with fresh makeup water for reuse in the wash process. Process wash water that is dumped to the sewer is treated to comply with all local regulations for water emissions.

· Hydrocycloning: A hydrocyclone is a vertical cylindrical vessel that uses gravity, centrifugal force and differences in material density to classify solid particles contained in a liquid stream. Hydrocyclones may be used on their own or in conjunction with sink/float systems to separate HDPE from other plastics and contaminants. They may also be used to remove contaminants from the wash water.

Air Classification

Air classification, or “elutriation” can occur at any of several points during the recycling process and may occur more than once. Air classification systems remove fiber, fines, powder, paper, film, and foam from HDPE regrind, which reduces overall contamination levels in subsequent processing stages making them more efficient. Air classification removes any lighter film and fiber portions present in HDPE flake that are not easily separated in subsequent washing and cleaning stages.

Drying

The dewatered flakes are passed through a dryer that utilized heated air to remove all residual surface moisture from the clean flakes. The clean flakes may be sold for use in this form or melt processed.

Melt Processing

Once the material is dried, it can be melt filtered and extruded into pellets. Extrusion melts the plastic flakes by conveying them via a screw through a heated barrel. At the end of the barrel the melt is forced through a holes in a die and cut as it exits in a water bath to form pellets. Melt filtering during extrusion to pellet is a process where the molten HDPE resin is passed through a series of fine filters/screens in the extruder to remove any remaining (unmelted) contaminants.

Blending/Compounding

In order to add value to the finished pellet, or to optimize the properties of the recycled HDPE resin for specific end-use applications, reclaimers may perform a blending or compounding stage prior to or during extrusion into pellets. Items that may be added during blending or compounding include, pigmentation, fillers, compatibilizers, ultra-violet (UV) light or heat stabilizers, or impact modifiers. The finished HDPE pellet is thoroughly dried and stored for shipment to converters (end-product manufacturers).

Conversion and End Use

Recycled HDPE is in the manufacture of numerous products and packages. The major generic end-use categories for recycled HDPE plastic are:

1)                Packaging products (blow-molded bottles);
2)                Extruded products (drainage pipe);
3)                Sheet and film products (blown film bags, extruded film products);
4)                Pallets;
5)                Plastic lumber products