ENStarting point
Release of a moisture-sensitive polymer should combine material identification, measurement method, validated drying conditions and control through to machine feeding. Temperature and time are process variables; the material's condition is the result to verify.
From measurement to batch release
Follow the sequence and open each stage to see its criteria.
- 01
Measurement method
Choose a method suited to the material and required limit.
- 02
Protected sample
Preserve the condition between sampling, transport and testing.
- 03
Drying conditions
Relate temperature, time, air and material load.
- 04
Controlled transfer
Prevent moisture reabsorption before processing.
- 05
Documented release
Record the result, method and decision for the batch.
Identify where the water is and why it matters
A batch may carry surface water after washing and moisture absorbed by the material. These conditions are not equivalent and may require different preparation stages. Record origin, storage time, packaging and exposure history. The assessment should consider the polymer and formulation, because different materials do not respond in the same way to the environment or drying.
BASF technical documentation describes the possibility of hydrolytic degradation in certain polyamides during processing when drying is insufficient. [1] This mechanism helps explain why the absence of visible water does not demonstrate suitable conditions. However, it does not justify attributing every decline in strength to moisture: composition, contamination and processing history also need investigation, particularly in recycled streams.
Define a method that actually answers the question
ISO 15512 covers methods for determining water in plastics in different forms, including granules and articles. Its public scope identifies the standard's purpose, but selecting and performing a method requires consulting the applicable requirements and a laboratory assessment. [2] The report should state the method, preparation, unit, sampling conditions and relevant limitations.
Do not automatically treat mass loss on heating as water: other volatile substances may contribute to the reading, depending on the material and procedure. For rapid factory control, establish its relationship with an appropriate reference method and verify its useful range. An instrument with good repeatability can produce a consistently unsuitable response if it measures a phenomenon different from the one limiting the process.
Protect the sample from collection to testing
Define sampling points that represent the decision: receipt, dryer outlet and near the machine feed. Use containers and procedures compatible with the measurement, minimising changes during transport and waiting. Record time and identification. If a sample remains exposed while awaiting analysis, the value may represent the laboratory bench rather than the batch in its processing condition.
Consider differences within the package or equipment. Sampling only the surface may not represent the entire contents. The sampling plan should account for heterogeneity and handling patterns. When a decision is close to the acceptance limit, examine method uncertainty and the risk of misclassification instead of treating the last decimal place as absolute certainty.
Validate the combined drying conditions
Temperature, time, airflow, air conditions and actual dryer loading influence the result. Dew point describes a characteristic of the drying air; it does not replace measurement of water in the polymer. The processing data sheet for a BASF Ultramid grade relates preparation to initial moisture and describes conditions specific to that material. Its values should not be copied for a recycled resin with a different composition. [3]
Develop the conditions with the material and equipment suppliers, considering thermal stability and use requirements. Assess behaviour at start-up, steady state and after interruptions. An excessively long cycle may also be unsuitable for a particular formulation. The objective is not to maximise temperature or time, but to achieve and preserve the necessary condition without compromising the material or wasting resources.
Calculate residence time and recognise the limits of the average
Hypothetical example: a hopper contains 600 kg of material effectively available to flow and feeds production at 150 kg/h. Calculated average residence time is 600 ÷ 150 = 4 hours. If withdrawal increases to 200 kg/h with the same usable mass, the average falls to 3 hours. Production scheduling therefore changes a preparation variable.
The average does not guarantee that all particles remain for that time. Flow distribution, low-movement regions and irregular feeding can produce different histories. Check the configuration with the manufacturer and confirm the material condition at the outlet. As another unit example, 0.05% by mass corresponds to 500 ppm by mass; this conversion is not a recommended limit for any polymer. The acceptance criterion must come from the application and its validation.
| Usable mass | Withdrawal | Calculated average residence time |
|---|---|---|
| 600 kg | 150 kg/h | 4 h |
| 600 kg | 200 kg/h | 3 h |
Avoid losing the result during transfer
A resin that leaves in suitable condition may change before reaching the machine. Assess containers, internal transport, waiting time and exposure during feeding. Control must cover the entire journey. If an interruption occurs, determine how the condition will be reassessed before restarting, following the procedure developed for the material.
The batch must remain identifiable after drying. Mixing prepared material with a newly opened package may invalidate its release condition and prevent failure investigation. Also record the destination of leftovers. Repeated drying without tracking history may hide variations and make it harder to interpret changes in colour, melt flow or properties that appear during conversion.
Investigate defects through controlled comparisons
Bubbles, surface marks or loss of properties may justify a moisture investigation, but do not prove its cause. Compare material as received and after preparation while controlling other relevant variables. Link each sample to its batch, time and process. If the correction does not produce the expected effect, examine other hypotheses instead of indefinitely increasing drying intensity.
Include tests linked to the part's function as well as appearance. For mechanical comparisons, follow the preparation and conditioning requirements of the method and specification. For materials whose behaviour depends on moisture, results obtained under different conditions may appear contradictory without any laboratory error. Traceability of these conditions is part of data quality.
Establish verifiable release
The control plan should state who measures, where they sample, which method they use, which criterion they apply and how they record exceptions. Define responses to equipment failure, out-of-condition results and material changes. Distinguish a process incident from definitive batch rejection: the next action depends on the possibility of correction and its technical assessment.
The PCR extrusion and final conversion receive a more predictable input when preparation is demonstrated. The expected deliverable is a verifiable material condition, accompanied by the history needed to repeat the result. This reduces dependence on trial-and-error adjustments and makes discussions among the supplier, production and quality teams more objective.
Sources and references
References accessed on 5 October 2026. The numbering in the text indicates the concepts supported by each source.
References to ISO standards use their publicly available scopes; full requirements should be consulted in the respective standards.
- BASF. Ultramid, Ultradur, Ultraform — Resistance to Chemicals. Manufacturer's technical information on interaction with water and hydrolytic degradation.
- ISO 15512:2019 — Plastics: determination of water content. Public scope of the standard.
- BASF. Ultramid B3EG6 — Product information and processing guidelines. Parameters for a specific grade, not automatically transferable to other materials.
Circuvia corporate content to support project discussions. Methods, acceptance criteria and applicable requirements are defined within the scope of each operation.