Criteria to Consider for HDPE

The objective of this document is to outline criteria to consider if a variant of the HDPE bottle or component of the HDPE bottle is being evaluated for recyclability in the existing HDPE (SPI resin identification code “2”) bottle stream. A bottle component is defined as a bottle accessory such as:

• Closures/Closure Liners
• Label/Adhesives
• Decoration
• Sleeves/Seals
• Attachments,
• or the bottle itself
  

Bottle color, multi-layers and coatings, chemical composition of the HDPE resin are also evaluated.

The goal of the APR in providing these criteria is to assist HDPE stakeholders in evaluating the potential impact of the variation on the recycled HDPE bottle stream towards the end result of maintaining the viability of the recycled HDPE bottle stream.

This document is to be used for information and guidance purposes only and is mainly directed towards packaging engineers, packagers using HDPE bottles, manufacturers of bottles and accessories, and resin manufactures. General Guidelines for recyclability for HDPE homopolymer and copolymer bottles, as well as other SPI coded bottles, are described in the Association of Postconsumer Plastic Recyclers (APR) “Design Guidelines for Plastic Bottle Recycling” brochure. It is available from the APR. While the APR design brochure describes HDPE variants that can have varying degrees of impact (positive and negative) on recyclability, this document focuses in more detail on
criteria to consider in evaluating the impact of a variant on the existing recycled HDPE stream. Using these criteria as general guidelines will assist in the design and execution of appropriate tests and trials to evaluate the effect of a variant. The APR in this document is not addressing the legal issue of what is or is not an SPI “2”, SPI coding has legal implications in some state laws.

The question as to what variants of HDPE bottles can be considered as recyclable in the present post-consumer HDPE bottle stream is being asked with increased frequency. The growing popularity of HDPE as a packaging resin and its successful recycling history has led the packaging industry to develop new HDPE bottles to suit both technical and marketing needs. By and large, HDPE recyclers, acting independently from each other, have responded to these changes based on their specific recycling process and the requirements of their end products or their customers’ end products. The APR, through this document, is placing before HDPE stakeholders some general criteria to consider when evaluating the impact of a HDPE variant on recyclability of the HDPE bottle stream. The APR encourages those with recyclability questions to contact the APR and the individual HDPE recyclers.

The potential impact of the variant and how to evaluate its impact will depend, in large part, on its effect in one or more of the following major areas:

• Consumer Market
• Collection System
• Recycler’s Process
• Fabricators Process/End Use
  

Each of these major areas will be discussed in more detail. However, the following assumptions have been made in generating the criteria. The assumptions are:

• The bottle will carry the SPI Resin Identification Code “2’, for HDPE regardless of the variant or will find its way into the stream as a HDPE look-alike.
• The new variant will be evaluated as if it were a contaminant in the existing,
• HDPE bottle stream while realizing that it may prove to be more recycle friendly than the existing variant.
• The concentration of the variant in the HDPE bottle stream will not be uniformly distributed and will be tested at levels higher than its expected market penetration.
  

Market information is important because it gives estimates of the expected levels of the variant in the recycled HDPE stream. These levels are needed to design meaningful trials/tests to evaluate the effect of the variant.

• Generally describe the expected market
• Generally describe type of bottles anticipated. Food? Household chemical?
• Expected material type of the bottle?
• Bottle sizes/shapes? Will the bottle be recognized as HDPE?

The consumer market information above will help stakeholders understand how the variant may or may not impact the collection system.

• Will it fit into current curbside collection systems?
• Will modifications be required in the collection infrastructure?
• Will the variant cause the bottle to have look-a-likes that could complicate collection or cause added contamination to the HDPE stream? For example, would there be filled HDPE that would have a specific gravity over 1.0 so that the material would sort into the PET bottle material stream?
• In the case of a HDPE chemical variant, could the variant have inherently more value than HDPE if sorted from the stream? Would the sorting be done at a MRF or recycler?

The level of the variant that a recycler experiences at any given time can depend on the source of the recycled HDPE bottles, There are two general sources of baled HDPE bottles, the makeup of which varies significantly between the general sources but also within a general source. The general types are:

Curbside Bale:
Potentially either a mixture of natural homopolymer HDPE and colored HDPE or sorted into natural HDPE bottles and colored HDPE bottles.

Mixed Bale:
Quality varies, composed of a mixture of PET soda and custom bottles, homopolymer HDPE (milk containers) and copolymer HDPE (detergent containers, for example).

Consideration should be given to the variants impact on each of a recyclers sorting and cleaning processes. Of course, each recycler’s process differs, so all of the items listed below will not apply to every recycler.

• Baling/Debaling
• Granulation (dry and wet)
• Dry label separation
• Washing equipment/wash chemistry
• Wastewater
• Solid wastes
• Separation of introduced non-HDPE layers or coatings
• Air quality
• Screening loss
• Is the cost to recycle impacted? New equipment or new wash chemistry needed?
• What is the effect on productivity?
• Is the value of the clean flake or melt filtered pellets impacted to include:
  • Particulates;
  • Environmental stress cracking
  • Density
  • Melting point
  • Deposits and plating on dies, pins, and molds
  • Screen life
  • Color, particularly for natural HDPE
  • Melt index
• Safety issues such as volatiles from degraded variant
• Are new test methods required to determine levels or residual levels of the variant?

The fabricator of a product may be a recycler using internally generated recycled HDPE or one who uses recycled HDPE from the marketplace. The major end uses of recycle HDPE are:

• Non-food bottles blow moldings
• Pipe extrusions
• Lawn and garden moldings and extrusions
• Film and sheet extrusions
• Lumber extrusions
• Pallets, crates, buckets moldings

The effect, if any of the variant, whether purposely left in the stream or resulting from incomplete removal, will have to be evaluated using different test protocols for each use. The variant may be found to be neutral or positive in some end uses but negative in others. If negative, then the question should be addressed as to the necessity to develop new, economically and technically viable sorting and/or cleaning technologies in order to allow the variant to be handled by the HDPE recycling industry as a whole.

Criteria to consider for evaluating the impact of the variant will depend in large part on the particular end use. Some end uses may be more tolerant of the variant than others. Most recyclers see variants in slugs—not uniformly distributed. Thus, the level of the variant should be tested in the end uses at some multiple of its expected market penetration. Multiples of 5 to 10 have been suggested and used.

Following are criteria to consider for the listed end uses.

The PCR bottle market is generally limited to non-food applications. Also consideration should be given to monolayer versus multi-layered constructions.

• Impact on flake and pellet making, including screen filtration
• Impact on extrusion blow molding process
• Impact on container properties to include:
  • Physical properties including top load
  • Color, if natural HDPE
  • Visual appearance
  • Environmental stress cracking
  • Bottle making productivity
    

• Impact on flake and pellet making, including screen filtration
• Impact on extrusion productivity, particularly for large diameter
• Impact on pipe properties including
• Compressive strength
• Impact strength
• Stiffness
• Environmental stress cracking
  

• Impact on flake and pellet making, including screen filtration
• Impact on injection molding productivity
• Impact on extrusion productivity
• Impact on fabricated structures including
• Tensile, flexural, and compressive strength
• Impact strength
  

• Impact on flake and pellet making, including screen filtration
• Impact on extrusion/processing
• Impact on thermoforming process
• Impact on gel formation and other visual defects
• Impact on properties including
• Impact strength
  

• Impact on flake making
• Impact on mixed material extrusion (mixed with other resins and/or filler and reinforcement)
• Impact of tensile, flexural, and compressive properties
  
  

Please contact APR for a list of reclaimers to continue discussions.