Identify which parameters are critical for the customer and process, how often they are tested and what happens when a result falls outside the specification. The system must be repeatable and supported by records.
The specification is the starting point
The organisation should define which product characteristics it controls and their acceptance limits. The parameters depend on the polymer, material form, process and customer requirements.
Parameters need a technical basis
Depending on the material, relevant parameters may include moisture, contamination, colour, density, melt flow rate, viscosity, other polymers, foreign matter and mechanical properties.
Sampling plan
A test result is reliable only when the sample represents the batch being tested. The system should define the sampling location, frequency, preparation method and sample identification.
Test methods
For each parameter, define the method, equipment, unit, acceptance criterion and responsibility. Where testing is outsourced, document the scope of work agreed with the laboratory.
Handling results outside the specification
The organisation should know who decides whether material is placed on hold, retested, reclassified, reprocessed or rejected. Decisions must remain traceable.
Trends matter as much as individual results
Analysis over time may reveal deterioration in feedstock or process quality before a formal nonconformity occurs. Comparisons by supplier, line, production shift or material type can help.
Quality and quantity balances describe different things
A quantity balance answers “where did the mass go?”, while quality control asks “does the material meet the requirements?”. In a mature system, these areas are connected but do not replace each other.
Key takeaway
Quality control should involve more than keeping test results. There must be a logical system from specification and sampling to the decision about a particular batch.