Color-measuring instruments ensure recycle quality.

Color is becoming a critical benchmark of quality in recycled resins, making colorimetric instruments indispensable tools in the plant and in the lab.

While color-measurement technology is not a new science, its use in recycling of post-consumer resins (PCR) is quite new. As the demand for consistent natural and other colors of recycled PET and HDPE increases, the need for standardization and codification of color measurement based on analytical dam becomes critical.

In the recycling industry's fledgling years, the human eye was the only means of determining color quality. Samples were graded A, B, or C and judgment calls were the standard of the day.

But today's recycled-resin customers--manufacturers of items ranging from detergent and shampoo bottles to fiberfill, carpeting, and cat-litter bags--have very specific color needs that must be addressed. Visual standards may be fine for a beauty contest, but the subjective approach had to give way to objective methods as the recycling industry began to recognize the need for a way to clearly communicate color-quality values backed by analytical data. Not only does codifying and standardizing color measurement lead to better communication of the color and quality of a recycled resin, but it also lends added credibility and professionalism to an increasingly sophisticated industry.

The right analytical tool had to be found--one that was rugged, portable, and very dependable. The solution turned out to be the handheld colorimeter. An example of this type of instrument, HunterLab's MiniScan, is now on the job at many recyclers' operations.

PCR USERS SET COLOR SPECS

In Albany, N.Y., wTe Recycling has been processing post-consumer resins for four years now. To keep pace with customers' quality needs, wTe invested in a portable colorimeter. The instrument generates Hunter "L" and "b" values that correspond to a lightness-darkness scale and yellow-blue scale, respectively. They are used by wTe in conjunction with other quality data to determine the suitability of both clear and colored post-consumer resins (PCR) for a variety of markets.

Says Brian O'Clair, laboratory/quality manager for wTe Recycling, "In addition to recycling PET, we have been recycling HDPE for PCR sales to extruders who do not have a need for clear resin. Much of the HDPE is used as basecups for 2-liter beverage bottles. Many of our customers need PCR with specific 'L' and 'b' values. As wTe recycles 30 million lb of PCR annually, we purchased the HunterLab MiniScan to provide hard-copy data on inventories shipped or allocated for shipment. The whole PCR industry has become more aware of color clarity as it relates to their own processes."

The handheld colorimeter can also be used to determine the most effective cleaning agents for PCR. Oakite Products, Inc. of Berkeley Heights, N.J., a supplier of detergents to many recyclers, purchased an instrument to ensure its detergent's effectiveness in removing contaminants that cause color variation. Color measurements of PCR are taken after cleaning, and the lighter flakes indicate the better cleaning agents. According to Karen Sohl, business manager for Oakite's Plastics Recycling Div., "HunterLab's sensor is used by recyclers and their suppliers as a scientific instrument for evaluating the recycling process. The MiniScan has become one of the standards in the industry."

ENSURING COLOR CONSISTENCY

Union Carbide Corp., headquartered in Danbury, Conn., also utilizes HunterLab's portable MiniScan at its plastics recycling plant in Piscataway, N.J. In the two years it has been in operation, this facility has succeeded in perfecting a post-consumer resin known as Curbside Blend PCR. Resins manufactured under this Union Carbide trademark are cleaned recycled polymers with very low levels of dirt. Consequently, Carbide's customers are assured of superior blend-to-blend consistency.

Because it is primarily dirt that gives recycled resin an unattractive appearance, the portable colorimeter has been a real boon in determining the dirt levels in raw materials during the recycle process. These measurements provide early data on PCR appearance prior to pelletizing. Thanks to the colorimeter, Union Carbide has moved from visual standards to a reliable and non-subjective method based on quantitative analysis.

In the case of unpigmented HDPE homopolymer, the recycled flakes are measured after grinding for their level of brightness before they pass on to the cleansing stage. This measurement also determines the amount of detergent needed for the cleansing process. After cleansing, the flakes are once again measured for color uniformity. If the flakes "Pass," as indicated by the colorimeter reading, they move on to the extrusion and pelletizing stage. Flakes that "Fail" the lightness requirement set by Union Carbide are sent back for additional cleaning.

COLOR-SORTED PCR

In our society, color is a strong marketing tool. Consumers want colorful products and packaging, so until recyclers could supply consistent color on a large-volume basis, recycling could not fully realize its potential. Union Carbide has been working closely with leading bottle-blowing companies to understand their colored-resin specifications. Based on feedback from these companies, Carbide developed "Prisma," a new interactive color system that provides highly consistent color quality in HDPE copolymer PCR derived from detergent bottles and other colored containers. Prisma works with the specific mix of PCR colors available to Union Carbide. The company developed empirical formulas for how to blend bottles of specific colors to obtain a consistent final color in a specific range of shades. Blow molders select the Prisma color they want from the menu of shades offered and Union Carbide will produce--and reproduce--the desired color, blend after blend.

Prisma's unique sort format separates the raw materials into different color groups and a portable colorimeter is used for process control. Selected colors and their tolerances for acceptable color differences are plotted on the Hunter L, a, b Color Scale to eliminate human subjectivity. Union Carbide also uses HunterLab's ColorQuest bench-top spectrophotometer in its quality-assurance laboratory for final testing before Prisma products are released to customers.

The color-consistency program for Union Carbide's natural-color PCR has been in place almost from the inception of the recycling plant. The company began using a color-measuring instrument on natural homopolymer HDPE two years ago and expanded its use to include Prisma copolymer HDPE six months ago. Quentin Eberhart of Union Carbide Polymers R&D says, "Recycling is a big industry. We believe one of our strengths is our ability to deliver a consistent product. Product properties are measured against specifications that include color. We sell our capability based on that. We also offer recommendations on types of instruments whenever people inquire about color-measuring equipment."

"The color business in recycling is just starting to develop," adds William Boyd, senior staff engineer for plastics recycling at Carbide. We expect it to be very dynamic, based upon the volume of detergent and other pigmented bottles coming in now from curbside collections. Many communities haven't started collecting them yet. Until now, it's been a limited market because of recyclers' inability to recycle these colored bottles effectively. The portable colorimeter helps Union Carbide maintain tight specifications by allowing color measurement during processing."