HDPE vs. Polyethylene: Material Differences and Comparisons

20 Sep.,2023

 

HDPE vs. Polyethylene: Recyclability and Sustainability

PE (polyethylene) in film form can be effectively recycled into second-grade production material once sorted. But sorting issues and the processing before pellet extrusion prevent much of this from being commercially viable. The film waste must be well sorted, to reduce the incidence of mixed material being reprocessed; otherwise, the properties of the resultant material are easily degraded. This sorting is not easy, as very low levels of colored films will significantly devalue a “clear” end product. The film materials also cause chronic tangling in the shredding process, requiring high labor costs to correct.

The sorted film is shredded, washed, dried, and extruded to form “new” pellets which are of high quality. They are unlikely, however, in the second incarnation to be used in film manufacturing or in food-grade applications. Most are used for low-grade applications in building and agricultural materials. 

Recycled material maintains a fairly high price, but the process is barely profitable because of the handling difficulties. Very little PE (polyethylene) is effectively recycled; instead, it ends up in incineration or landfill. Most kerbside recycling collection points do not accept PE (carrying any recycling mark or the ♶ identifier) but treat that which is left by consumers as waste material to be removed and disposed of.

HDPE (high-density polyethylene) film materials are generally used in heavier (or thicker)  sections and colored, and are relatively easy to sort for high purity. The process does not require the separation of colored, natural, and clear materials at the sorting stage—all colors are processed together.

Like PE, sorted plastic is first washed, then dried, and shredded to produce greater uniformity and easier processing. The shredded material is then heated to a melting point and extruded to form a standard molding-pellet feedstock. The equipment to perform this process is low cost, but there is considerable labor in the sorting stage—where much of the market value is added—as multi-polymer blend material has virtually zero value.

The end result is high-quality, second-grade material that generally has a dark color and can be used for a range of otherwise normal applications, substituting for virgin material, or more often as a second-grade minority component with otherwise new material.

All PE (polyethylene) materials are commercially produced from hydrocarbon source materials and represent a significant environmental burden. Very little HDPE (high-density polyethylene) is recycled, though claims of 28% recycling of milk containers are made in some markets. Despite this, overall estimates of recycling volume are unreliable and very low.

Overall, PE materials are highly recyclable and can produce good resultant products for 10 or more cycles (potentially many more, if perfectly sorted and treated gently). However, real recycling rates worldwide are minimal as a percentage of the total made. Most are lost to the environment, put in landfills, or burned for disposal or power generation.

HDPE vs. Polyethylene: Cost

Like all of the PE family, HDPE is a low-price material that is manufactured in huge quantities and is generally considered a commodity material. The price for virgin material is around $8.50 per kg, reduced to $2.50 for recycled material.

Polyethylene (PE) has a considerably lower cost than HDPE, generally selling as granules in the $0.90–$1.10 price range. Recycled clear PE is available at a similar or slightly lower price, and it is generally used as a 10–20% addition to virgin material, saving a few cents per kg.

Alternative Materials to HDPE and Polyethylene

Polyethylene (PE) has a wide range of applications and these suit different alternative materials. For films, some available options are: BOPP (biaxially oriented polypropylene), PVC (polyvinyl chloride), polycaprolactone, PET, and PLA (polylactic acid). For pipes and fittings, the alternative materials are: UPVC (unplasticized polyvinyl chloride), HDPE, PEX (radiation cross-linked PE), metal—copper, iron, plated and stainless steel, etc. For homewares, some alternative materials are: ABS (acrylonitrile butadiene styrene), PET, HIPS (high impact polystyrene), and PP (polypropylene).

HDPE (high-density polyethylene) has a wide range of applications, but they are narrower in scope, and alternatives are more straightforward. For most applications, alternatives are PE, PET, PEX, ABS, PP, and rubber-modified PP.

Summary

This article presented HDPE and polyethylene, explained what they are, and discussed the differences between the two materials. To learn more about HDPE and polyethylene, contact a Xometry representative.

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