OCC Contamination Standards: What Mills Actually Test For

Old Corrugated Containers (OCC) is the most traded recovered paper grade in the world. But not all OCC is created equal. The difference between a load that a mill accepts at full price and one that gets rejected or heavily downgraded often comes down to one thing: contamination. This article explains the ISRI standards, what mills actually test for, and how to minimize contamination in your supply.

The ISRI Standard for OCC (Item Code 11)

The Institute of Scrap Recycling Industries (ISRI) publishes the Scrap Specifications Circular, which defines acceptable contamination limits for all recovered paper grades. For OCC, the standard is clear and strict:

These thresholds are not suggestions. They are the baseline that mills use to accept or reject loads. A load that exceeds these limits can be rejected entirely, downgraded to a lower-value grade, or accepted only at a significant price discount.

What Counts as Prohibitive Materials?

Prohibitive materials are substances that, if present in OCC, can damage mill equipment, disrupt production, or compromise finished product quality. The ISRI standard defines these as materials that "by their presence, in any amount, may cause problems." In practice, this includes:

Plastic Film and Bags

Plastic film — including plastic bags, stretch wrap, and plastic sheeting — is the single most common contamination issue in OCC. When plastic reaches the pulping stage, it wraps around rotating equipment, jams screens, and can shut down production for hours. Even small amounts cause significant disruption. Mills test for plastic visually during receiving inspection and via equipment monitoring during processing.

Waxed and Treated Cardboard

Waxed cardboard (used for produce boxes, beverage packaging, and frozen food containers) does not break down properly during pulping. The wax coating separates from the fiber, creating "stickies" — tacky deposits that accumulate on papermaking equipment. Stickies are one of the most expensive contamination problems mills face.

Hazardous and Perishable Materials

OCC that has contained hazardous chemicals, pesticides, or perishable food creates health and safety risks and can contaminate the finished product. Mills reject these loads outright.

How Mills Test for Contamination

Visual Inspection: Mill receiving staff visually inspect bales for obvious contamination: plastic film, waxed cardboard, tape, and labels. Loads with visible prohibitive materials are often rejected before unloading.

Bale Sampling: Mills typically sample bales by hand-sorting a representative portion (50–100 pounds per bale) to quantify contamination. If prohibitive materials exceed 1% or total outthrows exceed 5%, the load is flagged.

Stickies Detection: Mills monitor the buildup of adhesive deposits on papermaking equipment. High stickies levels indicate contamination with waxed or adhesive-coated materials — a major quality issue that can result in equipment downtime.

Practical Strategies for Minimizing Contamination

Educate your collection network: Create clear signage: "OCC Only — No Plastic, No Waxed Cardboard, No Tape."

Invest in sorting: Hand-sort incoming OCC to remove obvious contaminants before baling. Clean OCC commands a premium, especially in tight markets.

Separate waxed cardboard: Waxed produce boxes and beverage cartons should be removed from OCC and directed to a separate stream.

Remove plastic film: Plastic bags, stretch wrap, and film should be removed before baling. These are the easiest contaminants to spot and remove.

Protect from moisture: Store baled OCC in a dry location. Exposure to rain increases moisture content and can introduce mold.

The Business Case for Clean OCC

The price differential between clean OCC and contaminated OCC is consistently significant. In tight markets, mills are more selective and the premium for clean material widens. Investing in quality control pays for itself through higher prices. A 2–3% improvement in contamination rates can translate to a $2–5 per ton price increase.

Conglobus International sources OCC11 and DSOCC from verified suppliers who meet strict contamination standards. If you are a mill or converter looking for consistently clean, quality-verified OCC, contact us.