A Comprehensive Guide to Plastic Dehumidifying Dryers for Various Materials
2025-03-31 Page view：
In the plastic processing industry, excessive moisture content in raw materials can lead to defects such as silver streaks, air bubbles, and even degradation of physical properties. Different materials have varying moisture absorption characteristics, and this article explores dehumidifying dryers suitable for five major categories of plastic materials, highlighting key adaptation strategies and technical considerations.
1. Engineering Plastics: The Precision Battle of Temperature and Humidity Control
Engineering plastics, such as Nylon (PA) and Polycarbonate (PC), have polar groups in their molecular chains, allowing them to absorb up to 2.5% moisture. These materials require a dual-tower molecular sieve dehumidifying dryer with a dew point of ≤ -45°C, along with automatic nitrogen protection to safeguard the material when the machine is idle.
For example, when processing PA66, temperatures above 120°C can lead to thermal oxidation degradation. To prevent this, a three-stage heating process is employed: 80°C (preheating) → 105°C (deep drying) → 90°C (constant temperature transport). A closed-loop dew point monitoring system ensures the moisture content is consistently controlled below 0.02%.
2. General-Purpose Plastics: A Cost-Effective Solution for Differentiated Drying
For materials like PP and PE, which are less moisture-absorbent, traditional hot air drying is typically sufficient. However, when dealing with transparent GPPS or materials with more than 30% color masterbatch, the residual moisture must be kept below 200ppm.
Experimental data shows that using a rotary dehumidifier to dry transparent PP at 65°C for 4 hours improves the material's light transmittance by 12%. For HDPE blends containing recycled materials, a pulse air drying system is recommended. This system uses intermittent strong airflow to penetrate the material layers, increasing drying efficiency by up to 40% compared to conventional equipment.
3. Recycled Crushed Materials: Filtering Impurities and Eliminating Thermal History
Recycled materials often contain impurities like oil and paper scraps, which can clog drying air pathways. For example, when processing automotive bumper scrap, a three-stage pre-treatment system is applied: vibration sieving (to remove metal), vortex separation (to remove lightweight impurities), and electrostatic separation (to remove PVC). This is followed by a gradient heating process: the first hour at 50°C to evaporate surface moisture, and the next three hours at 75°C to remove bound water. This process successfully reduces moisture content from 1.8% to 0.15%.
A key consideration is controlling the particle size of crushed material to 4-6mm. If the particles are too fine, it can lead to thermal short circuits in the air flow.
4. Biodegradable Plastics: The Delicate Balance of Low-Temperature, Slow Drying
PLA materials can experience molecular chain breakage above 70°C, and traditional drying methods may cause a reduction in viscosity. To prevent this, a cyclone diversion drying technique is used, creating a spiral airflow at 65°C within the drying chamber. This technique extends the material's residence time to 6-8 hours, while preventing localized overheating. Case studies show that this process improves the retention rate of viscosity in PLA from 82% to 97%, while reducing energy consumption by 30%.
For PBAT/starch blends, an additional -20°C condensing dehumidifying module is added to prevent moisture absorption and clumping of the starch.
5. Specialty Materials: Innovations in Customized Drying Systems
conventional equipment can result in significant heat loss—up to 40%. By using a double-insulated drying chamber combined with infrared heating compensation, heat efficiency can be improved to 85%.
When drying TPU materials, oxygen levels need to be kept below 100ppm to avoid yellowing. An inert nitrogen circulation drying system, equipped with an oxygen concentration sensor, helps maintain this critical threshold. For conductive materials like carbon fiber-reinforced PEEK, the drying chamber's walls should be coated with Teflon to eliminate static charge accumulation, ensuring even fiber distribution.
Plastic dehumidifying drying has evolved from simple temperature control to a complex system that integrates material property analysis, impurity treatment, and energy management. Understanding the unique "drying characteristics" of different materials is crucial for achieving the optimal balance between quality and cost. Looking ahead, with the advancement of intelligent drying solutions—such as AI-based dew point prediction and microwave-assisted drying—new breakthroughs in material processing precision and efficiency are on the horizon.
