Views: 0 Author: Site Editor Publish Time: 2026-09-22 Origin: Site
With rising global environmental regulations and growing consumer demand for sustainable products, biodegradable plastics such as PLA, PBAT, and PHA have gradually replaced traditional petroleum-based plastics in many industries. However, most manufacturers and product designers overlook one critical fact:biodegradable resins cannot be molded with standard molds and conventional injection molding processes.
Compared with common plastics like ABS, PP, and PC, eco-friendly biodegradable materials have completely different thermal stability, chemical properties, and mechanical characteristics. Directly using traditional mold designs often causes bubble defects, gas marks, part cracking, mold corrosion, high scrap rates, and unstable mass production.
This comprehensive blog summarizes the core differences between biodegradable and conventional plastic injection molding, shares professional mold design guidelines, analyzes the actual advantages and limitations of biodegradable materials, and provides practical selection advice to help you make accurate manufacturing decisions.
The fundamental molding and mold design gaps stem from the inherent material properties. Conventional plastics are designed for stable industrial mass production, while biodegradable materials are optimized for environmental degradation, sacrificing processing tolerance and mechanical stability.
Traditional petroleum-based plastics feature excellent thermal stability and a wide processing temperature window. They resist thermal decomposition during injection molding, with low moisture sensitivity and predictable, stable shrinkage rates. Most commodity plastics have good toughness and ductility, allowing them to withstand normal ejection pressure and minor structural stress without cracking or deformation. Even filled-grade traditional plastics only cause simple mold wear, with no corrosive chemical byproducts during production. These forgiving properties make them highly compatible with standard mold structures and universal molding parameters.
Biodegradable eco-plastics have obvious limitations in industrial molding. They have a very narrow thermal processing window and are extremely sensitive to high temperature, long melt residence time, and excessive shear force. Once overheated, the materials undergo thermal hydrolysis, producing acidic gas and carbon residues, which lead to surface defects and mold corrosion.
In addition, biodegradable resins absorb moisture rapidly in daily storage, causing silver streaks, bubbles, and material degradation if not fully dried. Most molded biodegradable parts are brittle with poor impact resistance, prone to cracking at sharp corners or during ejection. Many blended biodegradable plastics contain starch, calcium carbonate, or plant fiber fillers, which accelerate mold cavity wear and surface scratching.
Standard molds suitable for PP and ABS cannot support long-term, stable production of biodegradable parts. We have summarized targeted mold design adjustments for eco-plastic molding based on practical manufacturing experience.
Conventional plastic molding only requires ordinary pre-hardened steel such as P20 and 718H, with no strict anti-corrosion requirements. For glass-filled traditional plastics, H13 or 1.2344 wear-resistant steel is sufficient.
For biodegradable plastics, anti-corrosion and wear-resistant steel is mandatory. Thermal decomposition produces acidic substances that erode common mold steel. Mass production requires stainless mold steel like S136 or 1.2083 ESR to resist corrosion and filler abrasion. Mirror polishing is not recommended, as carbon residues easily adhere to ultra-smooth surfaces and cause frequent cleaning downtime. Fine matte polishing or standard VDI texture is the most practical choice. Regular anti-rust treatment is also required after production shutdown.
Traditional plastics tolerate various gate types and moderate shear heat, with flexible runner designs. In contrast, biodegradable materials are extremely sensitive to shear force and melt residence time.
To avoid material carbonization and weld line weakness, molds for biodegradable plastics require low-shear gating design. Short, streamlined runners are used to reduce melt stagnation time. Narrow pin-point gates that generate intense shear are not recommended. Edge gates, fan gates, and submarine gates are the optimal choices. If a hot runner system is required for high efficiency, valve gate hot runners are preferred to prevent material drooling and degradation.
Biodegradable materials produce far more gas during molding than conventional plastics. Standard vent layouts lead to trapped air, burn marks, gas lines, and short shots.
Molds for PLA and PBAT need expanded vent areas, increased vent quantity, and a controlled vent depth of 0.015–0.025mm. Additional vents must be added at weld line positions, fill endpoints, and deep rib dead corners. Removable vent inserts are highly recommended for quick carbon residue cleaning to stabilize continuous production.
Traditional plastics have a wide mold temperature adjustment range, and minor uneven cooling only causes slight warpage. Biodegradable plastics require precise, balanced temperature control, with a fixed mold temperature range of 40–60°C for most PLA and PBAT materials.
Uneven cooling and local hot spots at bosses, ribs, and thick walls directly trigger thermal degradation and internal bubbles. Overly fast cooling will generate severe internal stress, making already brittle parts easier to crack. Therefore, molds must adopt uniformly distributed cooling channels to eliminate hot zones and ensure consistent cooling speed for the entire product.
Due to the brittleness of biodegradable parts, standard structural designs for traditional products are no longer applicable. Manufacturers need to increase draft angles appropriately (1.5°–2° for textured surfaces) to avoid surface scratching during demolding. All sharp corners must be replaced with large rounded fillets to release stress concentration.
For the ejection system, larger-diameter and more evenly arranged ejector pins are required to disperse ejection force. Slow ejection speed is necessary to prevent top whitening and part cracking. Complex undercut structures with tight stripping are minimized to avoid tearing brittle eco-plastic parts.
Conventional plastics have fixed and stable shrinkage rates, enabling one-time accurate cavity compensation during mold processing. Biodegradable plastics have highly variable shrinkage, which fluctuates with melt temperature, packing pressure, and mold temperature. Mold cavities need reserved modification margins, and T1 trial tests are essential to confirm actual shrinkage data.
In terms of maintenance, biodegradable plastic molds require frequent cleaning to remove carbon and acidic residues. Immediate anti-rust protection is required after production, while traditional plastic molds only need routine simple maintenance.
Eco-friendly and compliant: Degrades under industrial composting conditions, helping brands meet ESG goals, global environmental regulations, and green certification requirements.
Strong market competitiveness: Meets the market demand for sustainable consumer goods, packaging, and eco-disposable products, expanding brand market access.
Qualified appearance performance: With professional mold design and process tuning, biodegradable parts can achieve appearance quality comparable to traditional plastic products.
Higher cost: Biodegradable resin prices are 1.5–3 times higher than ordinary PP and ABS, with additional costs for upgraded mold steel and frequent maintenance.
Poor mechanical and thermal performance: Brittle texture, low impact resistance, and low heat deflection temperature, unable to withstand high temperature and structural load.
Strict production requirements: Mandatory material drying, narrow processing windows, and higher scrap rates lead to lower production efficiency.
Usage restrictions: Most biodegradable plastics only decompose in industrial composting environments and cannot degrade quickly in household compost or landfills.
Single-use disposable products: eco-packaging, disposable tableware, cosmetic packaging, and promotional gifts
Projects with mandatory environmental compliance, green certification, or customer-specified sustainable material requirements
Low-load, room-temperature products with no high-strength and heat-resistance demands
Products whose waste can be centrally processed by industrial composting facilities
Structural functional parts requiring impact resistance, load-bearing, and long service life
Products used in high-temperature environments, prone to thermal deformation
Cost-sensitive mass-produced products with strict unit price control
Durable consumer goods designed for long-term repeated use
If you plan to switch to biodegradable plastics, do not directly open formal mass-production molds at the first step. It is recommended to use rapid prototype molds for small-batch testing to verify product appearance, structural stability, and molding defects. After confirming all performance indicators meet standards, upgrade to anti-corrosion hardened steel molds and optimize venting, cooling, and ejection structures for stable mass production.
Biodegradable plastics are a targeted sustainable solution rather than a universal replacement for traditional plastics. The essential differences in material thermal stability, chemical activity, and mechanical properties lead to completely different mold design, processing technology, and maintenance standards.
For eco-friendly, low-load, disposable products with environmental compliance demands, biodegradable plastics are a valuable and market-competitive choice. For functional, durable, cost-sensitive industrial products, conventional PP, ABS, and PC plastics remain more stable, economical, and reliable. Reasonable material selection and professional mold customization are the keys to balancing environmental value and manufacturing efficiency.
Q1: Can I use existing ABS/PP molds to produce biodegradable parts? A: Short-term sampling is feasible, but long-term mass production is not recommended. Standard molds lack sufficient venting, anti-corrosion performance, and optimized ejection structures, resulting in high defect rates and mold damage.
Q2: Why do biodegradable parts crack easily after molding? A: It is caused by the material’s inherent brittleness, excessive internal stress from unbalanced cooling, and unreasonable ejection force. Optimized mold fillet, draft angle and ejection system can effectively improve this problem.
Q3: Are biodegradable plastics truly environmentally friendly? A: Yes, but conditional. They can completely degrade only under professional industrial composting conditions. Without supporting disposal facilities, their environmental advantages cannot be fully realized.
Q4: Is the production cost of biodegradable plastic parts higher? A: Definitely yes. Higher resin prices, upgraded mold costs, frequent maintenance, and higher scrap rates all increase overall production costs, with the core value lying in green compliance and brand upgrading.
