What Limits the Color You Can Achieve on a Recycled Resin?

The customer approved a light blue on a plaque made with virgin resin, and the first production lot ran on recycled resin because purchasing found a better price. The part came out greenish, with dark specks and a different shade in every box. Production raised the masterbatch dosing, the cost per kilo shot up, the blue still failed to appear and the entire lot ended up in rework. The color they approved was never possible on that resin, and nobody said so before startup.

The final color on recycled resin is limited by the resin's base tone, its lot-to-lot variation and what it carries inside. Masterbatch covers and corrects up to a point; beyond it, the color you want demands a different resin or a different target shade.

The resin's base tone is the ceiling of the color

A virgin resin is practically colorless or translucent, and the pigment starts from zero. A recycled resin arrives with a color of its own: gray, yellow, greenish or brown, depending on where it came from, how many times it was processed and what pigments it carried in its previous life. That base color does not disappear when you add masterbatch; it adds to the new pigment and defines how far the final shade can go. That is why a light blue on gray recyclate comes out as a dull blue, and on yellowish recyclate comes out greenish.

Gray, yellow or brown: what the resin contributes before any pigment

The origin of the recyclate determines its base tone. A clean post-industrial material from a single source can be almost as neutral as virgin. A mixed post-consumer stream carries pigments from containers of every color, which melt together into a characteristic gray or brown. And any resin that has been through an extruder several times accumulates yellowing from thermal degradation. Before talking about color, it pays to know which of the three you have in the bag, because each one has a different ceiling.

Light, pastel and translucent colors: the first to be lost

The shades that depend on a clean base are the first to become unreachable. A bright white, a lemon yellow, a pastel pink or any translucent color need the resin to contribute nothing, and recyclate always contributes something. Dark, saturated and opaque colors, by contrast, have enough strength to prevail over the base. Knowing which side of the spectrum your customer's color falls on is the first question before quoting with recyclate.

Lot-to-lot variation turns an approved color into a range

With virgin resin, two bags of the same grade behave the same and the approved color repeats. With recyclate, each lot comes from a different mix of material and arrives with a different base tone. The same masterbatch, at the same dosing, produces one shade in this week's lot and another in next week's. That turns the approved color into a range, and if the customer approved an exact point, every lot outside that point is a complaint.

Why two bags from the same supplier give two shades

The recyclate supplier rarely controls base color as a quality variable; it controls melt flow index, moisture and, with luck, contamination. The tone is the result of what went into its grinder that week. If your supplier cannot give you a reference plaque for each lot, or does not separate by origin, the variation is part of the material and not a defect you can claim against.

Approving a tolerance range instead of an exact shade

The practical way out is to agree with your customer on a color tolerance range, measured with a spectrophotometer against a standard, instead of a single shade. You define how far the lot may deviate in lightness and in hue and approve it from the start, with plaques at the extremes of the range signed by both parties. With that, lot-to-lot variation stops being an argument and becomes a specification.

Contamination: what the resin carries inside

Beyond the base tone, recyclate can carry particles no pigment can hide: label remnants, adhesives, other polymers, gels, metals or fibers. They show up as dark specks, streaks or small bumps on the surface of the part, and they are more visible the lighter and smoother the color.

Specks, streaks and fish eyes: contaminants that color does not hide

A dark speck on a black part disappears; on a beige part it is a rejection defect. Raising the masterbatch dosing to hide it does not work: the pigment covers the background, but the contaminant is still there with its own color and its own texture. The only way to reduce it is at the source, with better filtered recyclate, or on your line, with finer filter screens that in turn raise pressure and energy consumption.

Residual pigment and polymer blends

The pigment the resin carried in its previous life is still active. A recyclate with traces of red shifts any new color toward orange or purple depending on what is added, and that deviation changes with every lot. A blend of polymers, for example polypropylene with traces of polyethylene, also produces zones of different crystallinity that reflect light differently and look like tone blotches even when the pigment is well dispersed.

Thermal degradation changes the shade during processing

Every pass through an extruder or an injection machine breaks polymer chains. A recycled resin already carries that history, and in your machine it accumulates once more. The visible result is yellowing and, in some cases, loss of gloss; the operational result is a melt flow index that no longer matches the supplier's data sheet.

Yellowing and loss of flow

Yellowing adds to the base tone and shifts light colors toward green or brown. Loss of flow changes how the masterbatch disperses: a concentrate formulated for a given melt flow index disperses worse in a resin that no longer has it, and streaks and zones of different intensity appear. A temperature profile adjusted downward and a short residence time reduce the damage; a resin that arrived already degraded cannot be recovered in your machine.

What you can achieve and how to ask for it properly

None of the above means recyclate is incompatible with good color. It means the color target is defined from the real resin, and not the other way around.

Dark, saturated and opaque colors: safe territory

Black, navy blue, dark green, deep red, medium gray and brown are colors achieved consistently on most recyclates, because they have enough strength to prevail over the base tone and enough opacity to hide small contaminants. Many industrial, agricultural, construction and logistics parts live in that territory, and there recyclate offers real savings without compromising appearance.

Reference plaque with the real resin, not with virgin

The rule that avoids the opening scenario is simple: the color is developed and approved on the resin that will be used in production. At Pigmentos Químicos we ask for a sample of the actual recyclate, formulate the masterbatch against that base and deliver the approval plaque made with it. If the customer approves on virgin and produces on recyclate, the approval is worthless.

Qualify the recyclate the way you qualify the masterbatch

Treat the recyclate supplier with the same rigor as the concentrate supplier: ask for a reference plaque per lot, measured melt flow index, maximum contamination percentage and origin of the material. Set the acceptable base tone range in your purchasing specification. When the recyclate has a specification, the color has a known ceiling and the masterbatch is formulated to reach it with margin.

If your customer approved a color on virgin and your production runs on recyclate, the approval was made on a resin that does not exist on your line. At Pigmentos Químicos we develop the color on your real resin and tell you from the laboratory which shade is achievable and within what range. Tell us about your part and your resin at https://pigmentosquimicos.com

Frequently asked questions

Can I achieve a white on recycled resin?

It depends on the base tone. On a neutral post-industrial material, a white with good opacity is achievable with the right dosing; on a gray or yellowish post-consumer material, the result will be an off-white or a bone shade, and it pays to agree on that tone from the start instead of chasing a pure white.

Does masterbatch correct the yellowing of recyclate?

It compensates partially in dark and saturated colors. In light colors, the yellowing adds to the shade and correcting it demands so much pigment that cost and gloss suffer. The real correction lies in the selection of the recyclate and in the process profile.

What percentage of recyclate can I blend with virgin without losing the color?

There is no universal figure; it depends on the recyclate's base tone and the target color. The right way to find out is to make plaques at different blend ratios, with your real resin and your masterbatch, and measure each one against the approved standard before fixing the recipe.