What are the types of environmentally friendly plastics in injection molds?

1, Biobased biodegradable plastics: a green closed-loop from raw materials to end-users
Biobased biodegradable plastics are made from renewable resources such as corn starch and sugarcane through microbial fermentation or chemical synthesis. Their core advantage is that they can return to the ecological cycle through composting or natural degradation at the end of their lifecycle, significantly reducing the risk of plastic pollution.
Polylactic acid (PLA)
Characteristics: PLA is polymerized from lactic acid monomers, with high transparency, good processability, and biocompatibility, but poor heat resistance (heat deformation temperature of about 55 ℃).
Injection adaptability: High mold temperature (80-120 ℃) and slow injection process should be used to avoid material embrittlement; The surface of the mold needs to be plated with hard chromium or coated with PVD to reduce mold sticking.
Application case: A certain brand of 3D printing pen shell adopts PLA injection molding. By optimizing the layout of the mold cooling water channel, the surface glossiness of the product is increased by 30%, while achieving 100% compostable degradation.
Polyhydroxyalkanoates (PHA)
Characteristics: PHA is synthesized by microorganisms and has excellent biocompatibility and heat resistance (thermal deformation temperature can reach 120 ℃), but the cost is relatively high.
Injection adaptability: It is necessary to control the mold temperature between 60-80 ℃ to avoid material degradation; Adopting a conformal cooling system to ensure uniform shrinkage of the product.
Application case: A medical enterprise uses PHA injection molding to produce biodegradable suture packaging boxes, and integrates anti slip and brand identification by laser engraving texture on the mold surface.
Starch based plastics
Characteristics: Mainly composed of starch, with added plasticizers and degradation promoters, low cost but weak mechanical properties.
Injection compatibility: High filling ratio (starch content ≥ 60%) and short cycle molding process are required to avoid material moisture absorption and deformation.
Application case: A fast food brand uses starch based plastic injection molded disposable tableware. Through optimized design of the mold parting surface, the demolding force of the product is reduced by 40%, and the occurrence of flash defects is minimized.
2, Physical recycling of plastics: the core carrier of circular economy
The physical recycling of plastics involves processes such as mechanical crushing, cleaning, and granulation to reprocess waste plastics into recycled particles, which has significant cost advantages. However, it is necessary to solve the problems of material performance degradation and impurity control.
Recycled polypropylene (rPP)
Characteristics: rPP comes from waste household appliances, car bumpers, etc., with better heat resistance and rigidity than native PP, but poorer fluidity.
Injection adaptability: High back pressure (10-15MPa) and high screw speed (300-400rpm) are required to improve the uniformity of the melt; The mold gate should be designed as a fan-shaped or point gate to reduce weld lines.
Application case: A certain automotive interior supplier uses rPP injection molded door panel substrate and optimizes the mold hot runner system to reduce product weight by 15% while meeting VOC emission standards.
Recycled polycarbonate (rPC)
Characteristics: rPC is mainly recycled from waste optical discs and electronic casings, with high transparency and impact resistance, but is prone to hydrolysis.
Injection compatibility: It is necessary to strictly control the moisture content of the raw materials (≤ 0.02%) and use vacuum drying technology; The surface of the mold cavity needs to be coated with titanium to enhance corrosion resistance.
Application case: A certain electronic brand uses rPC injection molding for mobile phone back covers. Through mold shape following cooling technology, the product warpage is reduced to within 0.1mm, and the yield rate is increased to 92%.
Regenerated Polyethylene Terephthalate (rPET)
Characteristics: rPET is derived from discarded beverage bottles and has high transparency and barrier properties, but poor heat resistance (thermal deformation temperature of about 70 ℃).
Injection compatibility: nucleating agents need to be added to improve crystallinity; The mold cooling water channel needs to adopt a spiral layout to shorten the molding cycle.
Application case: A certain daily chemical enterprise uses rPET injection molded shampoo bottles, and through nanoscale polishing treatment on the surface of the mold, the surface roughness of the product is reduced to Ra ≤ 0.05 μ m, achieving a mirror effect.
3, Chemical recycling of plastics: the ultimate solution to overcome performance degradation
Chemical recycling decomposes waste plastics into monomers or small molecule compounds through processes such as pyrolysis and gasification, and then re aggregates them into high-performance recycled materials. The product performance can be close to that of primary materials, but the cost is relatively high.
Chemical recycling of polyethylene (crPE)
Characteristics: crPE is produced by pyrolysis of waste plastics, with high purity and low odor, and can replace food grade HDPE.
Injection compatibility: Low shear screw design is required to reduce molecular chain breakage; The depth of the mold exhaust groove should be controlled at 0.02-0.03mm to avoid burning.
Application case: A packaging company uses crPE injection molded food containers, and through the multi cavity balance design of the mold, the weight deviation of the product is controlled within ± 0.5g, meeting FDA certification requirements.
Chemical recycling of nylon (crPA)
Characteristics: crPA comes from waste fishing nets and carpets, with high strength and wear resistance, but high water absorption rate.
Injection compatibility: requires drying treatment (moisture content ≤ 0.03%); The mold core needs to be treated with hard chrome plating to enhance wear resistance.
Application case: A certain sports brand uses crPA injection molded sole components, and optimizes the mold hot runner temperature control system to reduce the fluctuation of product shrinkage rate to ± 0.2%, improving the stability of sports performance.
4, Core principles for selecting environmentally friendly plastics
Performance matching: Select materials based on product usage scenarios such as heat resistance, impact resistance, and transparency. For example, PLA or PHA should be preferred for medical devices, while rPP or crPA can be used for automotive interior parts.
Process compatibility: Evaluate the compatibility between material flowability, shrinkage rate, and mold design parameters, such as the use of large gates and slow injection for high filling rPP.
Cost effectiveness: Balancing material costs, processing costs, and environmental value, for example, rPET has a 30% lower cost than PLA, but a longer degradation cycle.
Regulatory compliance: Ensure that materials comply with international environmental standards such as REACH and RoHS, such as FDA or GB 4806 certification for food contact materials.