To produce non-yellowing transparent PC/PMMA parts, the essence lies in a systematic engineering battle against material “degradation” and “aging.” The key to manufacturing transparent PC/PMMA parts that do not yellow involves comprehensive control from raw materials and processing to post-treatment.
| Control Stage | Main Measures | Principle of Action |
|---|---|---|
| Raw Material Control | Use high-purity raw materials; add efficient antioxidants (e.g., hindered phenols) and UV stabilizers (e.g., benzotriazoles, benzophenones). | Reduce impurities and degradable structures at the source, cutting off the chemical pathways for yellowing. |
| Processing Technology | Ensure thorough drying of raw materials (e.g., PC at 120°C for 3-4 hours). | Avoid hydrolysis degradation at high temperatures due to moisture. |
| Precisely control processing temperature (e.g., PC typically at 280-310°C), avoiding local overheating or prolonged residence time. | Prevent yellowing caused by thermo-oxidative degradation of the polymer. | |
| Use high-gloss molds (cavity surface roughness Ra ≤ 0.05 μm) and optimize gate and runner design. | Reduce flow resistance and shear heat, avoiding surface defects and degradation. | |
| Post-Treatment | Perform annealing on PC parts (temperature at 110-120°C, duration depending on wall thickness). | Eliminate internal stress, preventing future stress cracking and accelerated aging. |
Underlying Causes of Yellowing
- Polymer Self-Degradation: During high-temperature processing, the molecular chains of PC and PMMA may break, forming yellow-colored chromophores. PC is more prone to thermo-oxidative degradation, while structural defects in PMMA molecular chains (such as head-to-head connections, unsaturated end groups) are the main cause of decomposition and yellowing at high temperatures.
- Impact of Additives: Some antioxidants and lubricants, if poorly compatible or not heat-resistant themselves, may precipitate or decompose, leading to increased haze or yellowing.
- Processing Factors: Moisture in raw materials, excessively high processing temperatures or prolonged residence times, and shear overheating can directly trigger or accelerate degradation.
💡 Advanced and Specific Formulation Strategies
If your product has higher requirements, consider the following directions:
- High Thermal Stability Synthesis of PMMA: The core lies in controlling the polymerization process to reduce molecular chain defects. For example, through innovations in high-temperature continuous bulk polymerization processes or using comonomers (such as copolymerization with N-substituted maleimides) to improve heat resistance.
- Transparent, Anti-Yellowing PC/PMMA Alloys: The key is combining the high toughness of PC with the surface hardness and weatherability of PMMA, but compatibility issues must be resolved. Patents show that high transparency and anti-yellowing can be achieved by adding specific compatibilizers (e.g., styrene-maleic anhydride copolymer, SMA) and compound UV stabilizers.
- Nanomaterial Modification: Adding a small amount (e.g., 0.5%-2%) of nano-silica can improve stress distribution, enhance light transmittance, and reduce haze.
⚠️ Details Requiring Special Attention
- Raw Material Drying is Crucial: This is the most basic yet most error-prone step. Strictly follow the material specifications.
- Temperature is a Double-Edged Sword: On the premise of ensuring smooth mold filling, use the lower limit of the recommended temperature range and minimize the residence time of the melt in the barrel.
- Mold Maintenance Cannot Be Ignored: Regularly maintain and polish the mold surface to avoid scratches affecting the part’s appearance.
- Clean Equipment Promptly: Before changing materials or shutting down, thoroughly clean the barrel and screw with purging compound to prevent carbonization of residual material from contaminating new products.
Producing transparent parts that do not yellow is a systematic project. If you can share more details about the specific application of your part (e.g., automotive lamp cover, optical lens), expected lifespan, and the main challenges (yellowing during processing or yellowing after a period of use), I can provide you with more targeted analysis.