Overview
EN ISO 1599:1999 (ISO 1599:1990) defines a laboratory method for measuring viscosity loss on moulding of cellulose acetate plastics. The procedure quantifies polymer depolymerization that can occur during thermal moulding - a change that commonly increases brittleness in finished parts. The test is applicable only to cellulose acetate that is essentially free of additives or fillers and has an acetic acid yield > 50%. The material is plasticized with dimethyl phthalate, moulded under defined temperature, pressure and time, then ground and analysed. Viscosity ratios before and after moulding are determined according to ISO 1157 and used to calculate percentage viscosity loss.
Key topics and technical requirements
- Scope limits: Suitable only for cellulose acetate without interfering additives/fillers and with acetic acid yield above 50%.
- Plasticizer: Dimethyl phthalate is used in the moulding formulation.
- Moulding conditions: Specified preheat and mould temperatures, contact and full pressure stages; full pressure ≥ 8 MN/m² on the moulding surface; moulding time varies with thickness.
- Sample preparation: Two accepted methods for incorporating plasticizer; sample moisture must be low (≤ 0.5%) to avoid defects. For some methods the powder must pass a 710 µm sieve.
- Post-mould processing: Cool under controlled conditions, grind moulded specimens to < 0.9 mm, and dry (typically 70 °C for 2 h).
- Viscosity measurement: Use solvents and procedures of ISO 1157 (viscosity number and ratio). Solutions of original and moulded material are prepared and flow times measured.
- Result expression: Percentage viscosity loss = 100 × (Yr,a – Yr,b) / Yr,a, where Yr,a is the original viscosity ratio and Yr,b after moulding. Report is the mean of two valid determinations; if they differ by >10% of the mean, perform two additional determinations.
- Limits: Precision (inter-laboratory) not established - caution advised for contractual/specification use.
- Safety: Procedure uses flammable solvents (propan-2-ol, dichloromethane) and requires appropriate safety controls.
Practical applications
- Quality control of cellulose acetate resins and moulded parts to detect thermal degradation.
- Process optimization and troubleshooting for injection or compression moulding of cellulose acetate formulations.
- R&D for formulation screening (e.g., evaluating processing stability or selecting suitable plasticizers).
- Acceptance testing when ensuring batch-to-batch consistency for medical, consumer or optical cellulose acetate components.
Who uses this standard
- Materials testing laboratories and QC departments in plastics manufacturing.
- Compounders and formulators working with cellulose acetate.
- R&D teams evaluating thermal stability and processing windows.
- Certification bodies and technical experts performing product assessments.
Related standards
- ISO 1157 - Plastics: Cellulose acetate in dilute solution - determination of viscosity number and viscosity ratio (used for viscosity measurements).
- ISO 585 - Determination of moisture content.
- ISO 565 - Test sieves (mesh size references).
Keywords: EN ISO 1599:1999, ISO 1599:1990, cellulose acetate, viscosity loss on moulding, dimethyl phthalate, viscosity ratio, ISO 1157, plastics testing.