For over two decades, high-density polyethylene (HDPE) and polyvinyl chloride (PVC) have been the materials of choice for nearly all household detergent and cleanser packaging, largely because their combination of low cost, chemical resistance, and processability was a fit for the low-margin products. Change is unfolding, though, as many detergent suppliers, even those of lower-cost brands, now are specifying polyethylene terephthalate (PET) and clarified polypropylene (C-PP) for their packaging.

Marketing is the driver behind the shift, as PET and, to a lesser degree, C-PP offer higher transparency and gloss than HDPE, with PET tapped more often because of its wider processing knowledge base. These attributes already have heightened PET and C-PP’s value in food packaging and other applications where product image plays a vital role with consumers. PVC offers the sought-after transparency and gloss but is mostly avoided because of the political issues surrounding it.

Significantly, cost differences between the incumbent materials and the challengers have shrunk, especially with PET. PET prices have even dropped below those for PVC in some regions, notes Hubert Zarzecki, export manager for two-stage stretch blow molding machine (SBM) manufacturer Stecca, Saint-Quentin, France. “[This] is why PET is [penetrating] the detergent market.” While Stecca’s machines have been used for water, vegetable oil, and carbonated soft-drink packaging, Zarzecki says the firm is seeing higher demand in detergent packaging applications.

That observation is supported by the “Plastic Containers” report released last September by The Freedonia Group, Cleveland, OH. It predicts that PET will displace HDPE as the leading polymer for containers by 2006, with expanded use in household-chemicals packaging as one of the leading drivers.

Caroline Wheelers, marketing manager at Thornton and Ross, which owns the Stardrops brand of all-around cleaners popular in the U.K., says improved PET pricing was one of the reasons it switched from PVC. “PET was chosen for its improved clarity and for environmental reasons,” she says, referring to its recyclability. 600-mL containers for Stardrops are blow molded by Owens-Illinois Plastics in Chalgrove, England. The container is based on the PVC container design, but features improvements such as a larger label panel. The design also allowed a flip-top closure, rather than a screw top, to be used.

Steve Carter, sales director for Europe and the Middle East at Owens-Illinois Plastics, says the processor invested £6 million ($9.5 million) last year to increase capacity for injection SBM household-cleaner bottles in the U.K. The processor’s addition of high-cavitation preform tooling for trigger-spray bottles follows a similar investment in the Netherlands. Owens-Illinois has also made SBM equipment investments, primarily single-stage machines from Nissei.

Stecca supplies two-stage machinery for outputs under 5000 bottles/h, but PET detergent bottles are mostly made on single-stage equipment. Since processors that have long served this market have used extrusion blow molding (EBM) machinery, they will require SBM equipment if customers specify or switch to PET bottles.

In the U.K., blow molder Inblow Form Ltd., Wrexham, Wales, late last year began processing 750-mL and 1-L C-PP handleware bottles for a surface cleaner from MPM Consumer Products. Inblow Form sales director Ken Mitchell says PVC, PET, and PP were considered, but HDPE was ruled out as the package had to be transparent. Milliken Chemical, which supplies the clarifier used in the PP, provided processing expertise.

Inblow uses Uniloy Milacron EBM machinery modified for C-PP processing. Though some machine suppliers — most notably Bekum — market SBM machinery specifically for PP, most PP bottles are extrusion blow molded.

PP can be processed on modified EBM machinery designed for pe. Some of PP’s advantages are its lower density and higher stiffness, but its low-temperature impact strength is not as good as that of pe, and processors may need new extrusion heads to accommodate PP’s higher die swell. Blow molds usually require sharper and harder bite edges to process PP.