PLA/PBAT blended biodegradable plastics are widely used in disposable tableware, packaging products and daily necessities due to their natural biodegradability and environmental friendliness. These materials have poor heat resistance, sensitive melt fluidity, strong moisture absorption and easy thermal degradation, with processing technology differing greatly from traditional plastics. Improper control causes yellowing, brittleness, melt flow interruption, fragile products, excessive shrinkage and surface bubbles/silver lines. Strict control of raw material treatment, temperature range, injection parameters, mold conditions and post-production management ensures products with qualified appearance, stable toughness and intact biodegradability.
Raw Material Drying and Storage ControlBiodegradable plastics absorb moisture faster than ordinary plastics, with excessive moisture triggering hydrolysis at high temperature, breaking molecular chains, reducing product toughness and causing internal bubbles and surface silver lines. Low-temperature dehumidification drying is used at 60-75℃ for 4-6 hours, controlling moisture content below 0.015%. Dried materials are sealed and insulated to prevent secondary moisture absorption. Recycled material proportion is limited to 15%, with crushed materials requiring uniform particle size screening and re-drying. Repeatedly recycled materials with reduced toughness are not suitable for stress-bearing products.
Barrel Temperature Precise ControlPLA/PBAT has poor thermal stability, prone to yellowing, carbonization and viscosity decline under high temperature, with a narrow molding temperature range. Barrel temperature is controlled at 165-195℃: feeding section 165-175℃, melting section 175-185℃, nozzle temperature 170-180℃, never exceeding 200℃. Lower barrel temperature below 150℃ for heat preservation during shutdown to avoid long-term retention and material deterioration. Use low-temperature PE for machine cleaning instead of high-temperature rigid plastics. Insufficient temperature causes poor fluidity, insufficient filling and prominent welding lines, while excessive temperature leads to yellowing, brittleness and reduced mechanical properties.
Plasticizing Screw Parameters AdjustmentBiodegradable materials are highly sensitive to shear force, with excessive shear destroying internal blended structures and reducing product flexibility. Adhere to low speed and low back pressure: screw speed 40-70rpm, back pressure 0.2-0.6MPa, meeting basic mixing needs without forced mixing. Use conventional gradual screws instead of high-shear mixing screws to maintain stable PLA/PBAT coexisting structures, retaining original material mechanical properties and preventing product hardening and cracking.
Injection Pressure and Speed ControlBiodegradable melt has moderate flow rate and small filling resistance, without needing high pressure/speed. Excessively high pressure causes large internal stress, demolding deformation and excessive flash, as well as warpage during storage. Conventional injection pressure is 60-95MPa, adjusted according to wall thickness: increased for thin-walled products, reduced for thick-walled necessities. Multi-stage low-speed filling is adopted to avoid jet flow and internal stress. Light pressure and short-time packing are used, with gradually decreasing pressure to prevent molecular orientation disorder and later shrinkage deformation.
Mold Temperature and Cooling SpecificationsMold temperature is controlled at 25-50℃, with water chillers for constant temperature control in high-temperature workshops. Low mold temperature accelerates surface solidification, stabilizes product size and shortens production cycles. Cooling time is 2-3 seconds per millimeter of wall thickness to ensure complete shaping before ejection. Biodegradable products have slow post-demolding shrinkage, so insufficient cooling causes ejection marks, deformation and uneven bending. Exhaust grooves are set at filling ends and corners to discharge gas and prevent scorching.
Clamping Force and Ejection System Requirements
Biodegradable materials have small melt expansion force, so actual clamping force is reduced by 20% on calculated values to avoid mold parting surface damage. Brittle finished products use flat ejector pins and ejector blocks instead of single-point thin thimbles. Ejection speed is kept stable and slow to prevent puncturing and surface damage, with optimized demolding draft angle and reduced cavity surface roughness for smooth demolding.
Production Environment and Finished Product Storage NotesWorkshops are kept ventilated and dry with humidity controlled at 45-65% to slow down moisture absorption of raw materials and products. Newly molded products are placed flat for natural cooling without stacking. Finished products are stored in cool, dark environments away from sunlight and high temperatures to prevent early degradation, softening and deformation. Strictly distinguish biodegradable materials from ordinary plastics to avoid cross-mixing affecting degradation characteristics.
Common Forming Defects Quick SolutionsOptimize drying process to solve bubbles and silver lines; reduce processing temperature and shear parameters to improve brittleness; increase forming temperature and injection pressure to improve insufficient filling; balance mold temperature and reduce packing time to correct shrinkage and warpage; increase mold exhaust, reduce local temperature to eliminate scorching marks.
Processing Points SummaryPLA/PBAT biodegradable plastic injection molding core is low-temperature forming, low-shear plasticization, low-pressure slow filling and low-temperature shaping, different from traditional high-temperature/high-pressure processing. Refined full-process management ensures production of qualified environmentally friendly products while retaining degradation performance and mechanical toughness, suitable for large-scale production of various degradable daily necessities and packaging parts.
