Contaminant Quantification
Unusable coarse material is separated from the pulp slurry during laboratory recyclability testing to determine the processable yield. The macro-reject fraction represents the percentage of dry weight of a packaging sample that is retained on a screen with specific slot dimensions, typically one hundred and fifty micrometres. This fraction includes unpulped paper flakes, plastic fragments, and adhesive particles that cannot be processed into new paper sheet products.
Measuring this value determines the yield of recycled fiber.
Screening Performance
Disintegrated stock must be washed carefully through the screen plate to ensure that loose fibers are washed away and only the true rejects are held back. In laboratory trials, the macro-reject fraction is calculated by drying the retained material in an oven and weighing it. A high value suggests that the packaging material has high wet strength or is covered with thick protective plastic laminates.
If the paper flakes do not dissolve easily, they will be discarded along with the plastics, which leads to fiber loss. Recyclability grading schemes penalize products that generate a high reject percentage because they reduce the efficiency of industrial papermaking.
Process Cost
Fibers lost to the reject stream must be replaced by virgin pulp or higher-quality waste papers. Therefore, a low reject percentage directly correlates with a more economical recycling process.
