Biodegradable Film Blowing Machine for PLA & PBAT

Applications

Processing biodegradable polymers on a blown film line is fundamentally different from running PE. PLA melts at 160-180°C and begins thermally degrading above 190°C — a window just 20-30°C wide. PBAT processes at a wider range (140-180°C) but is stickier than PE, building up on die lips faster. Standard polyolefin screws with compression ratios of 3:1 to 4:1 generate excessive shear heat that pushes PLA past its degradation point within minutes. This machine uses a modified low-shear screw with a compression ratio of 2.2:1 to 2.8:1 — specifically designed to plastify bioplastics without destroying them.

Who This Machine Is For

• Film producers entering markets with plastic bag bans. Countries across the EU, Southeast Asia, and Africa are mandating biodegradable or compostable packaging. A PE-only machine cannot process PLA or PBAT — the screw geometry is wrong. This machine gives you a production line that meets the regulatory requirement without risking polymer degradation and wasted raw material.

• Converters supplying supermarkets and retailers with compostable packaging. Large retail chains increasingly require compostable produce bags, shopping bags, and packaging films with EN 13432 or ASTM D6400 certification. The film properties start with the machine — if the extruder degrades the polymer during processing, the film will fail certification testing regardless of the raw material quality.

• Manufacturers diversifying from PE-only into biodegradable product lines. You keep your existing PE lines running. This machine handles the biodegradable portion of your production, allowing you to serve both conventional and compostable packaging markets without cross-contamination between resin types.

Who Should NOT Buy This Machine

• If your market does not require biodegradable or compostable film. This machine is purpose-built for bioplastics. Running standard PE on it is possible but suboptimal — the low-shear screw plastifies PE more slowly than a standard polyolefin screw, and output will be 10-15% lower than an equivalent high-speed PE film blowing machine of the same extruder size.

• If you need high-volume output above 150 kg/h. Biodegradable materials run slower than PE because the narrow processing window limits screw speed — run too fast and shear heating pushes PLA past its degradation point. For high-volume PE production, a dedicated ABA blown film machine is more productive.

• If your biodegradable raw material supply is inconsistent. PLA and PBAT from different suppliers have different melt flow indices and additive packages. If you change suppliers frequently, each switch requires temperature profile recalibration. A machine running one consistent bioplastic formulation produces reliable film; a machine running a different blend every week produces scrap.

Technical Advantages

Low-Shear Screw That Preserves Polymer Molecular Weight

Compression ratio of 2.2:1 to 2.8:1 versus 3:1 to 4:1 for standard PE screws. Bioplastics — especially PLA — are sensitive to shear-induced chain scission. When a standard PE screw compresses and shears PLA at high RPM, the polymer chains break, molecular weight drops, and melt strength collapses. The bubble becomes unstable not because of cooling or air ring issues, but because the polymer itself has degraded before it even exits the die. A low-shear screw generates less frictional heat at the same throughput, keeping the melt temperature within the safe processing window. The trade-off: plastication is gentler, so maximum output is lower than a PE-optimized screw of the same diameter.

Precision Temperature Control Across a Narrow Window

PID controllers hold each barrel zone within ±1°C of setpoint. PLA has a processing window of roughly 160-185°C — below 160°C, unmelted granules reach the die; above 190°C, thermal degradation begins and the polymer yellows, loses strength, and produces acidic byproducts that corrode the screw and barrel. Standard temperature controllers with ±3-5°C hysteresis are acceptable for PE (processing window ~120-230°C) but inadequate for PLA — a 5°C overshoot into the degradation zone damages the material. Each heating zone on this machine uses PID autotuning with SSR (solid-state relay) output, not mechanical contactors, to achieve the ±1°C precision that biodegradable materials require.

Corrosion-Resistant Metallurgy for Acidic Degradation Products

Screw and barrel are nitrided or bimetallic — not standard carbon steel. When PLA thermally degrades, it produces lactic acid. PBAT degradation produces adipic acid and terephthalic acid. These acidic byproducts corrode standard nitrided steel surfaces over months of operation, pitting the screw root and barrel wall. Corrosion pits trap degraded polymer that then contaminates fresh melt — visible as black specks in the finished film. The nitrided surface treatment on the screw and barrel resists this acidic attack. For producers running high percentages of PLA (above 70% of the blend), a bimetallic barrel with a higher chromium content provides additional corrosion resistance.

Real Production Issues It Solves

• PLA film yellowing during continuous production. After 4-6 hours of continuous operation, PLA film begins to turn yellow — even though the temperature controllers show the correct setpoint. The cause: polymer residence time in the barrel. PLA degrades over time at processing temperature, not just when temperature overshoots. The low-shear screw minimizes frictional heating, and the screw geometry is designed for shorter residence time — deeper flight channels in the feed section move material through the barrel faster. If yellowing still occurs after 8 hours, reduce screw RPM by 5-10% and check that the barrel cooling fans are functioning — a failed cooling fan on one zone is the most common cause of gradual heat build-up.

• PBAT sticking to the die lip and causing film defects. PBAT is inherently stickier than PE at processing temperature. As it exits the die gap, it accumulates on the die lip, creating drag lines on the bubble surface — visible as vertical streaks in the finished film. The wider die gap (1.8-2.2mm versus 1.2-1.5mm for PE) reduces exit velocity and die lip contact. Additionally, the die lip is chrome-plated and polished to a mirror finish — the smoother the surface, the less PBAT adheres. Operators should wipe the die lip every 4-6 hours during PBAT production; waiting a full shift results in heavy build-up that requires stopping the line to clean.

• Moisture in starch-based compounds causing bubble pinholes. Starch-filled biodegradable compounds absorb ambient moisture during storage. When moist pellets enter the extruder, the water flashes to steam at melt temperature, creating pinholes in the bubble. The vented barrel option on this machine allows moisture to escape before the melt reaches the die — a vent port in the barrel decompression zone releases steam while the downstream compression section re-pressurizes the melt for die flow. If pinholes persist, pre-dry the material at 60-80°C for 2-4 hours before feeding.

Production Scenarios

How It Works

1. Material Preparation: Biodegradable pellets — PLA, PBAT, or pre-compounded blends — must be stored in sealed bags with desiccant. Unlike PE, which tolerates ambient humidity, biodegradable materials absorb moisture that causes processing defects. A dryer or vented barrel is standard equipment, not optional.

2. Low-Shear Melting: The single-screw extruder with compression ratio 2.2:1 to 2.8:1 gently plastifies the polymer. Barrel temperature zones are set to the specific material's processing window — typically 155-185°C for PBAT/PLA blends. SSR-driven PID controllers maintain ±1°C precision. Screw RPM is deliberately limited: biodegradable materials cannot be run at the speeds PE machines achieve because shear heating escalates exponentially with RPM.

3. Moisture Venting (if equipped): In the decompression zone of the vented barrel, a port allows steam to escape before the melt reaches the die. The downstream compression section re-pressurizes the melt for uniform die flow. Vented barrels are recommended for starch-filled compounds and any material stored in humid environments.

4. Bubble Formation: Melt exits the spiral mandrel die with a wider die gap (1.8-2.2mm) to reduce shear at the die lip — important for sticky PBAT grades. Dual-lip air ring provides external cooling. The frost line is set higher than for PE because biodegradable melts have lower melt strength and need more distance to stabilize.

5. Winding: Oscillating haul-off distributes gauge bands. Surface winder with controlled tension — biodegradable films are softer than PE and more susceptible to stretch deformation during winding. Tension is set 20-30% lower than equivalent PE film settings.

Optional Configurations

Customer Case

Hanoi, Vietnam — 2024. A packaging converter supplying supermarket chains with compostable shopping bags replaced a standard PE line (modified in-house for PLA, with limited success) with this purpose-built biodegradable film blowing machine.

The modified PE machine had a standard compression-ratio screw that sheared PLA past its degradation point within hours. Temperature overshoot from mechanical contactor controllers caused intermittent yellowing. The purpose-built machine's low-shear screw, SSR temperature control, and nitrided barrel eliminated all three issues. The EN 13432 compostability certification — impossible on the modified PE line due to inconsistent mechanical properties — passed on the first submission with the new machine. The customer now supplies three supermarket chains with certified compostable produce bags.

Why Choose Mingyang Machinery

• 20+ years focused on blown film. Screw design for biodegradable polymers is a specialty within our engineering team — not an afterthought on a PE machine platform.

• CE certified. Full documentation for EU and international customs clearance.

• Material testing before purchase: Send us your biodegradable resin or compound. We run it on our lab machine and report processability, recommended temperature profile, and expected output before you commit to a purchase.

• Engineer support: Post-installation video call, remote diagnostics, optional on-site dispatch. Biodegradable processing troubleshooting is different from PE troubleshooting — our support engineers are trained on both.

• 60+ countries: Container loading, sea freight, destination port coordination.

Frequently Asked Questions

Material and Processing

What biodegradable materials can this machine process?

PLA (polylactic acid), PBAT (polybutylene adipate terephthalate), PBS (polybutylene succinate), PHA (polyhydroxyalkanoates), starch-based thermoplastic compounds, and blends of these materials with calcium carbonate or other mineral fillers. The machine is not limited to one specific biodegradable resin. However, each material or blend requires its own temperature profile calibration — do not assume the settings for a PBAT/PLA 70/30 blend will work for a PLA-dominant formulation.

Can I run standard PE on this machine as well?

Yes, but output will be 10-15% lower than a PE-optimized machine of the same extruder size. The low-shear screw plastifies PE more gently than a standard polyolefin screw. If your production is split 50/50 between biodegradable and PE, two dedicated machines are more productive. If you only occasionally run PE (less than 20% of production volume), running it on this machine is acceptable.

What happens if PLA overheats in the barrel?

PLA thermally degrades above 190°C through a chain-scission mechanism. The polymer chains break, molecular weight drops, and the melt loses strength — the bubble becomes unstable. The degraded polymer produces lactic acid, which corrodes the screw and barrel. You will notice three symptoms: the film turns yellow (visual), the bubble pulsates and frost line becomes uneven (process), and eventually black specks appear in the film (corrosion contamination). If you see all three, stop production, purge thoroughly with a stable material, and inspect the screw for corrosion pitting.

Why does PBAT stick to the die lip more than PE?

PBAT has lower crystallinity and higher surface energy than PE at processing temperature — it wets the metal die surface more readily. As it exits the die gap, a thin layer adheres to the lip and oxidizes, turning brown over time. This oxidized layer creates drag on the bubble surface, visible as vertical streaks. The wider die gap and chrome-plated mirror-polished lip on this machine reduce but do not eliminate PBAT build-up. Operators should wipe the die lip every 4-6 hours during PBAT production.

Certification and Quality

Will film produced on this machine pass compostability certification?

Certification (EN 13432, ASTM D6400) depends on the raw material formulation, not the machine. However, a poorly designed machine that degrades the polymer during processing will cause certification failure because the degraded film has inconsistent mechanical properties and unpredictable disintegration behavior. This machine preserves the polymer's molecular weight throughout processing — the film properties are determined by the raw material, not degraded by the extruder.

Why is temperature control more critical for biodegradable film than PE?

PE processes across a ~110°C window (120-230°C). PLA processes across a ~20-30°C window (160-185°C). A temperature overshoot of 5°C in PE is negligible. The same overshoot in PLA pushes the polymer past its degradation point. This is the single most common reason modified PE machines fail at biodegradable film production — the temperature control system is adequate for a 110°C window but inadequate for a 25°C window.

Operation and Maintenance

How often does the screw need inspection for corrosion?

Every 6 months for machines running more than 70% PLA. Every 12 months for machines running primarily PBAT blends. PLA degradation produces more acidic byproducts than PBAT. Pull the screw, inspect the root surface in the metering section (the highest-temperature zone where degradation occurs), and measure screw diameter at three points along the metering section. Diameter reduction of more than 0.3mm indicates active corrosion — replace the screw before pitting contaminates the melt stream.

What cleaning procedure is recommended between biodegradable and PE production?

Purge with a thermally stable LDPE at 180-190°C for 30-40 minutes. The LDPE pushes out residual biodegradable material and coats the barrel and screw surface, protecting against acidic residue. Do not purge with HDPE — its higher processing temperature (200-230°C) will degrade any residual PLA in the barrel. Do not leave the barrel empty and hot after biodegradable production — the residual film on the barrel wall degrades and produces acid that attacks the metal surface.

Get a Configuration and Material Test

Send us your production parameters. If you have a specific biodegradable material or blend, we will test it on our lab machine and report processability before you order:

• Biodegradable material type and supplier (PLA / PBAT / PBS / starch compound / custom blend)

• Target film width (lay-flat, mm) and thickness (microns)

• Required output (kg/h or monthly tonnage)

• Compostability certification target (EN 13432 / ASTM D6400 / other)

• Local climate — ambient humidity and temperature range in your factory

• Electrical supply (voltage, frequency, phases)

carrie@jymingyang.com | +86-189-6169-1127