Necessary equipment list for biodegradable plastic twin screw compound production line

Setting up a biodegradable plastic twin screw compound production line demands a meticulously planned equipment list that covers every stage from raw material handling to finished pellet packaging. Biodegradable resins such as PLA, PBAT, PBS, and starch-based blends behave differently from conventional polyolefins: they are hygroscopic, thermally sensitive, and prone to hydrolytic degradation. Each piece of equipment on the line must be selected with these material characteristics in mind. Kerke, a Wanplas factory with over 12 years of specialized experience in twin-screw compounding extruders, has installed more than 2,000 machines across 70+ countries and operates a 19,997+ square meter manufacturing facility. As a recognized top-5 supplier in China for twin-screw extruders, Kerke brings deep engineering know-how to biodegradable compound production line design. This article provides a comprehensive, item-by-item equipment list covering every component necessary to build a fully operational biodegradable plastic twin screw compound production line, from storage silos and dehumidifying dryers through twin-screw extruders, pelletizing systems, cooling conveyors, and quality control instruments. Whether you are planning a 500 kg/h pilot line or a 2,000 kg/h industrial-scale production facility, this guide walks you through every machine, specification, and selection criterion you need.

1. Production Line Architecture Overview

A biodegradable plastic twin screw compound production line is an integrated system of interconnected equipment stages that transform raw resin pellets, powders, and additives into uniform, high-quality compounded pellets ready for downstream conversion. The architecture follows a linear process flow, but each stage incorporates specific design features to accommodate the thermal and rheological sensitivity of biodegradable polymers. Understanding the complete process flow is essential before diving into individual equipment specifications.

The production line begins with raw material reception and storage, where incoming resin is unloaded, inspected, and transferred to sealed storage silos or bins. From storage, material is conveyed to drying systems that reduce moisture to safe levels for extrusion. Dried material is then metered through precision feeding systems into the twin-screw extruder, where melting, mixing, devolatilization, and chemical reactions occur. The melt passes through a screen changer for filtration, then enters the pelletizing system where it is cut into pellets, cooled, and conveyed to finished product storage.

The following table summarizes the seven major equipment stages and their primary functions:

Each stage must be specified in concert with the others. Oversizing the extruder while undersizing the feeding system, for example, leads to inconsistent melt quality and formulation drift. Undersizing the drying system relative to extruder throughput guarantees moisture-related defects. The equipment list in the following sections addresses each stage with specific model recommendations, technical parameters, and selection criteria.

2. Raw Material Reception, Storage, and Drying Equipment

The first equipment category on any biodegradable compound production line handles raw material reception, storage, and drying. Biodegradable resins, particularly PLA and PBS, absorb atmospheric moisture aggressively. Processing these materials without adequate drying leads to hydrolytic chain scission, molecular weight loss, reduced mechanical properties, and visible defects such as foaming, silver streaks, and discoloration in the final pellets. The storage and drying equipment list must therefore be designed with moisture control as the primary engineering objective.

2.1 Storage Silos and Bins

Raw material storage begins with sealed, moisture-proof silos or bins constructed from stainless steel or food-grade polyethylene. For a typical mid-scale production line processing 1,000 kg/h, a minimum of three storage silos is recommended: one for the primary resin (PLA, PBAT, or PBS), one for fillers or reinforcement materials (talc, calcium carbonate, starch), and one for additive masterbatches or powdered additives. Each silo should be equipped with a desiccant breather or nitrogen purge connection to maintain a dry internal atmosphere.

Silo capacity should provide at least 48 hours of production buffer. For a 1,000 kg/h line, each primary resin silo should hold 20 to 25 tons. Silos must include level sensors (capacitive or radar type) for inventory monitoring, and bottom discharge cones with a minimum 60-degree slope to ensure free-flowing material discharge without bridging, which is a common problem with starch-based powders.

2.2 Dehumidifying Dryers

Dehumidifying dryers are the most critical equipment in this stage. Unlike conventional hot-air dryers, dehumidifying dryers use a closed-loop air circuit passing through a desiccant bed (typically molecular sieve) to achieve dew points of -40 degrees Celsius or lower. This ultra-dry air is heated and circulated through the resin bed, driving moisture out of the polymer matrix effectively.

The drying capacity must match the extruder throughput. For biodegradable resins, the following moisture targets must be achieved before the material enters the feeding system:

For a 1,000 kg/h PLA compounding line, a dehumidifying dryer with a minimum 4,000 kg hopper capacity is required to ensure continuous material supply during the 4 to 6 hour drying cycle. The dryer must include a closed-loop air system with a regenerative desiccant bed, process air heater with PID temperature control, and an insulated drying hopper to minimize heat loss. Air flow rate should be calibrated to 1.2 to 1.5 cubic meters per minute per kilogram of material in the hopper.

2.3 Vacuum Conveyors and Material Handling

Material transfer between silos, dryers, and feeders must be accomplished without re-introducing moisture. Vacuum conveying systems are preferred over open-belt or bucket elevators because they operate in sealed pipelines that can be purged with dry air. A typical vacuum conveyor system includes a vacuum pump (side-channel blower or claw pump), stainless steel transfer piping with smooth interior surfaces, a receiver hopper with a filter assembly, and a discharge valve. For biodegradable powder materials such as starch or calcium carbonate, the conveyor must include a sintered stainless steel filter with a self-cleaning pulse-jet function to prevent powder buildup and blockage.

The conveying rate should be 1.5 to 2 times the extruder throughput to allow batch transfer cycles without starving the downstream feeders. For example, a 1,000 kg/h extruder requires a vacuum conveyor rated for 1,500 to 2,000 kg/h. Piping diameter should be 60 to 90 mm for pelletized resins and 90 to 120 mm for powder materials to prevent bridging and flow interruption.

3. Precision Dosing and Feeding Systems

Precision dosing and feeding systems determine the formulation accuracy of the final biodegradable compound. Biodegradable formulations typically contain 50 to 85 percent base resin, 10 to 30 percent filler or reinforcement, 1 to 5 percent compatibilizer, and 0.5 to 3 percent of various additives including lubricants, antioxidants, and color masterbatch. Even small deviations in additive ratios can significantly affect the mechanical properties, degradation rate, and processing behavior of the final compound. The feeding system must therefore deliver consistent, accurate, and repeatable material flow to the extruder feed throat.

Kerke offers five types of feeding systems, each suited to different material types and formulation requirements:

3.1 Loss-In-Weight Feeders

Loss-in-weight (LIW) feeders are the gold standard for biodegradable compounding lines. These feeders operate on a gravimetric principle: the entire feeder assembly is mounted on a high-precision load cell that continuously measures weight loss as material is dispensed. A closed-loop control system adjusts the feeder screw speed to maintain the target feed rate within +/- 0.5 percent accuracy. For biodegradable formulations requiring precise additive dosing, LIW feeders are mandatory.

A typical LIW feeder configuration for a 1,000 kg/h line includes a 50-liter hopper, a co-rotating twin-screw feeding mechanism (for powders and pellets), a 3 kg load cell with 0.05 percent resolution, and a refill system that automatically tops up the hopper without interrupting the feeding cycle. For the main resin feed, a larger LIW feeder with a 150-liter hopper and a single-screw feeding mechanism is recommended. For liquid additives such as plasticizers or crosslinking agents, a liquid LIW feeder with a gear pump dosing head is used.

3.2 Volumetric Feeders

Volumetric feeders dispense material at a fixed volume per unit time, calibrated against a known bulk density. While less accurate than LIW feeders (+/- 2 to 3 percent typical accuracy), they are suitable for materials with consistent bulk density and for applications where slight formulation drift is acceptable. In biodegradable compounding lines, volumetric feeders are typically used for the primary resin stream, where the material is pelletized and has a stable bulk density.

3.3 Side Feeders

Side feeders, also known as twin-screw side feeders, introduce materials into the side of the extruder barrel rather than through the main feed throat. This configuration is essential for feeding fillers such as talc, calcium carbonate, glass fiber, or starch powder into the melt stream. By introducing fillers downstream into the already-molten polymer, side feeders improve wetting and dispersion while reducing dust and feed throat blockage. For biodegradable compounds containing 20 to 40 percent mineral filler, a side feeder rated at 200 to 400 kg/h is typically required.

3.4 Crammer Feeders

Crammer feeders are designed for low-bulk-density materials such as starch foam, biodegradable film flake, or lightweight powder blends. These feeders use a tapered screw geometry with a crammer auger that compacts the material before it enters the extruder feed throat. For lines processing recycled biodegradable film or starch-based pre-blends, a crammer feeder increases the effective feed density by 2 to 3 times, enabling the extruder to achieve rated throughput.

3.5 Liquid Feeding Systems

Liquid feeding systems are used to inject liquid additives such as plasticizers, coupling agents, or liquid colorants directly into the extruder barrel. A liquid feeding system includes a precision metering pump (gear pump or piston pump), a stainless steel storage tank with agitation, a heated supply line to maintain liquid viscosity, and an injection nozzle mounted on the extruder barrel. For biodegradable compounds requiring liquid plasticizer addition of 2 to 5 percent, a liquid feeder with 0.5 to 5 kg/h capacity and +/- 1 percent accuracy is appropriate.

4. Co-Rotating Twin-Screw Extruder — Core Compounding Unit

The co-rotating twin-screw extruder is the heart of the biodegradable compound production line. Unlike single-screw extruders, which rely on drag flow for material transport, co-rotating twin-screw extruders use intermeshing screw elements that create positive displacement, self-wiping action, and controlled shear mixing. This makes them ideal for biodegradable polymers that require thorough distributive and dispersive mixing without excessive thermal exposure. The modular screw and barrel design allows customization of the processing path for specific biodegradable formulations.

Kerke’s KTE series co-rotating parallel twin-screw extruders range from KTE-16B (laboratory scale) to KTE-135D (high-capacity industrial scale). For biodegradable compounding, the KTE-95D and KTE-135D are the most commonly selected models. The following specification table details the KTE-95D, a versatile mid-range extruder suitable for production lines with 500 to 1,000 kg/h output:

4.1 Screw Design for Biodegradable Plastics

The screw configuration is the single most important factor determining mixing quality and thermal exposure in a twin-screw extruder. Kerke designs each screw assembly using computer-aided engineering software, selecting from a full range of conveying elements, kneading blocks, reverse elements, and mixing rings. For biodegradable compounds, the screw layout typically follows this architecture:

• Feed and conveying zone (L/D 4 to 8): Deep-flighted conveying elements transport material from the feed throat into the barrel with minimal shear, preventing premature melting or bridging.
• Melting and initial mixing zone (L/D 8 to 16): Narrow-pitch conveying elements followed by 30-degree and 60-degree kneading blocks initiate melting and begin distributive mixing. This zone must apply enough shear to melt the resin without causing thermal degradation.
• Side feed and dispersion zone (L/D 16 to 24): A vent port precedes the side feed opening. After filler introduction, 90-degree kneading blocks and special mixing elements provide dispersive mixing to break down filler agglomerates.
• Devolatilization zone (L/D 24 to 32): A reverse conveying element creates a melt seal before the vacuum vent, preventing vent flow. The vent section uses deep-flighted conveying elements to maximize surface area for volatile removal.
• Final mixing and metering zone (L/D 32 to 40+): Additional kneading blocks ensure homogenization, followed by conveying elements that build pressure for the die and pelletizing system.

4.2 Barrel Temperature Control

Precise barrel temperature control is critical for biodegradable polymer processing. PLA, for example, has a narrow processing window of 170 to 200 degrees Celsius. Exceeding 210 degrees Celsius causes rapid thermal degradation and discoloration. Each barrel zone on the KTE-95D features independent PID temperature control with cast aluminum heaters providing heating and internal water cooling channels providing active cooling. The temperature control accuracy is +/- 1 degree Celsius at steady state. This level of control prevents localized hot spots that could trigger thermal degradation of heat-sensitive biodegradable polymers.

4.3 Vacuum and Devolatilization System

Biodegradable compounding generates significant volatiles, including residual moisture, monomers, and degradation byproducts. The KTE-95D is equipped with a vacuum devolatilization system featuring a water-ring vacuum pump capable of achieving 0.08 to 0.1 MPa ultimate vacuum. The vacuum port is positioned in the devolatilization zone and includes a vent insert designed to prevent material plugging. A condensate collection system captures extracted volatiles, preventing them from entering the vacuum pump. For formulations with high volatile content, a two-stage vacuum system with a backing pump and a roots pump can be specified.

5. Melt Filtration and Screen Changer Systems

Melt filtration removes contaminants such as unmelts, cross-linked gel particles, metal fragments, and foreign matter from the polymer melt before it reaches the pelletizing die. In biodegradable compound production, filtration is particularly important because contaminants cause defects in thin-wall products such as biodegradable film, food packaging containers, and agricultural mulch film. Even small gel particles can create weak points in biodegradable film, causing premature failure during service.

5.1 Screen Changer Types

Two primary screen changer designs are used in biodegradable compounding lines: manual slide-plate screen changers and continuous (also called back-flush or double-piston) screen changers. Manual slide-plate changers require a brief production stoppage to switch the filter screen, making them suitable for smaller lines or formulations with low contamination levels. Continuous screen changers use a double-cavity design that allows filter switching without stopping the extruder, maintaining steady melt flow and pressure.

For biodegradable lines running 500 kg/h or above, a continuous screen changer is strongly recommended. The stoppage required for a manual screen change causes a pressure spike that can damage biodegradable polymer chains through excessive shear. Additionally, the restart after a screen change produces off-spec pellets that must be segregated and reworked, reducing overall yield.

5.2 Filter Mesh Selection

Filter screen mesh selection depends on the contaminant size to be removed and the acceptable pressure drop. For biodegradable compounds destined for film applications, a mesh range of 80 to 120 (180 to 125 microns) is typical. For injection molding grade compounds, 40 to 80 mesh (425 to 180 microns) is usually sufficient. Finer mesh provides better filtration but increases pressure drop and requires more frequent screen changes. The screen pack configuration typically uses a layered arrangement: a coarse backing screen (20 to 40 mesh) supporting a fine filtering screen (80 to 120 mesh), held in place by a breaker plate.

For compounds containing high filler loadings or recycled biodegradable content, an automatic back-flush screen changer is recommended. This system periodically reverses a small portion of the melt flow through the filter to clean the screen surface, extending screen life from hours to days and reducing downtime for screen changes.

5.3 Melt Pump Integration

A melt pump (gear pump) installed between the screen changer and the pelletizing die stabilizes melt pressure and flow rate, which is critical for producing uniform pellets. The melt pump absorbs pressure fluctuations from the extruder and delivers a constant-volume output to the die. For biodegradable compounding lines, a melt pump with hardened gear teeth, heated housing, and a pressure transducer feedback loop is recommended. The pump should be sized to handle 1.2 to 1.5 times the maximum extruder throughput to allow for future capacity expansion.

6. Pelletizing and Cutting Systems

The pelletizing system converts the continuous melt strand exiting the extruder die into uniform pellets. The choice of pelletizing method significantly affects pellet shape, size uniformity, bulk density, and downstream processing behavior. For biodegradable plastics, pellet quality is especially important because irregular pellets or pellets with tails cause feeding problems in injection molding machines and film extruders. Kerke offers six pelletizing system configurations, each suited to different materials, throughput rates, and pellet quality requirements.

For high-capacity biodegradable compound production, the KTE-135D extruder paired with an underwater pelletizing system is the most common configuration. The following specification table details the KTE-135D:

6.1 Pelletizing Method Comparison

The following table compares the six pelletizing methods offered by Kerke, with specific applicability to biodegradable plastic compounds:

6.2 Underwater Pelletizing System Components

For biodegradable compound production at industrial scale, the underwater pelletizing system is the preferred configuration. This system cuts the melt strand at the die face underwater, with the pellets immediately quenched and transported by water flow to a centrifugal dryer. Key components include a heated die plate with multiple pelletizing holes, a cutter head with adjustable knife pressure, a water chamber with temperature-controlled circulating water, a pellet water slurry pump, a centrifugal dryer, and a water treatment system.

The die plate is heated to maintain melt temperature at the die face, preventing premature solidification that would cause die hole blockage. For biodegradable polymers, the die plate temperature is typically set 5 to 10 degrees Celsius above the polymer melting point. The cutter head uses 4 to 8 knives made of tungsten carbide or tool steel, rotating at 1,500 to 3,000 rpm depending on pellet size requirements. Pellet diameter is determined by the die hole diameter and is typically 2.5 to 4.0 mm for biodegradable compounds. Pellet length is controlled by the ratio of cutter speed to extruder throughput.

6.3 Water Ring Die Face Hot Cutting

For medium-capacity biodegradable lines (200 to 2,000 kg/h), the water ring die face hot cutting system offers an excellent balance of pellet quality and equipment cost. In this system, the melt is cut at the die face by a rotating knife, and the pellets are thrown into a ring of cooling water that quenches and transports them. The pellets are spherical with a smooth surface, and the system requires less space and lower capital investment than an underwater pelletizing system. However, the water ring system is limited to lower throughput rates and may produce more oversized pellets or fines if the knife-to-die clearance is not precisely maintained.

7. Pellet Cooling, Conveying, and Storage Equipment

After pelletizing, the pellets must be cooled, dried, conveyed, and stored before packaging. The cooling and conveying equipment ensures that pellets reach a stable temperature and moisture level suitable for storage and downstream processing. Improper cooling leads to pellet clumping, bridging in storage silos, and moisture absorption that can compromise the quality of biodegradable compounds.

7.1 Vibrating Fluid-Bed Coolers

For air-cooled pelletizing systems, a vibrating fluid-bed cooler is used to reduce pellet temperature after cutting. The cooler consists of a vibrating perforated deck through which ambient or chilled air is blown upward. Pellets are conveyed along the deck by the vibration while being cooled by the air flow. For biodegradable pellets, the outlet temperature should be below 40 degrees Celsius to prevent clumping. A fluid-bed cooler with 3 to 5 square meters of deck area can handle 500 to 1,500 kg/h of pellets, depending on the bulk density and heat capacity of the compound.

7.2 Centrifugal Dryers

For water-based pelletizing systems (underwater and water ring), a centrifugal dryer removes surface water from the pellets. The dryer uses a rotating basket with internal lifters that throw pellets against a screen while air is drawn through the pellet bed. A well-designed centrifugal dryer reduces pellet surface moisture to below 0.1 percent. For biodegradable pellets, the dryer should include a heated air supply (40 to 60 degrees Celsius) to provide gentle secondary drying and prevent moisture absorption during the drying process.

7.3 Pellet Conveying Systems

Dried and cooled pellets are conveyed to storage or packaging using pneumatic conveying systems or belt conveyors. Pneumatic conveying is preferred for biodegradable pellets because it operates in sealed piping, minimizing moisture pickup. The conveying system should use low-velocity dense-phase conveying (2 to 5 meters per second) rather than dilute-phase conveying (15 to 25 meters per second) to prevent pellet attrition and fines generation. For a 1,000 kg/h line, a pneumatic conveyor with 50 mm piping diameter and a rotary valve feeder is typically specified.

7.4 Finished Pellet Storage and Packaging

Finished pellets are stored in sealed silos or directly packaged in moisture-proof bags. For bulk storage, stainless steel silos with desiccant breathers maintain pellet dryness during storage. For bagged product, an automatic bagging machine with a weighing system and heat sealer is used. Each bag should include a desiccant packet and be constructed from moisture-barrier material (such as aluminum-lined woven polypropylene) to maintain pellet quality during shipping and storage. For biodegradable pellets, storage time should be minimized, and silos should be purged with dry nitrogen for long-term storage exceeding 30 days.

8. Auxiliary and Utility Equipment Checklist

Beyond the primary production equipment, a biodegradable compound production line requires a range of auxiliary and utility equipment to support continuous, efficient operation. These systems are often overlooked during initial project planning, but their absence or undersizing can cause production bottlenecks, quality issues, and unplanned downtime.

8.1 High-Speed Mixer

A high-speed mixer (also called a high-intensity mixer) is used for pre-blending powdered components before extrusion. For biodegradable compounds, the mixer blends the base resin powder or pellets with fillers, additives, and color masterbatch to create a homogeneous pre-mix that feeds consistently into the extruder. A typical high-speed mixer for a 1,000 kg/h line has a 500-liter working volume, a 30 to 45 kW motor, and operates at 500 to 1,500 rpm. The mixer should include both high-speed and low-speed agitators for optimal mixing efficiency and a discharge valve compatible with pneumatic conveying.

8.2 Water Chiller

Water chillers supply chilled water for barrel cooling, pelletizing water, and dryer after-cooling. The chilling capacity must account for all cooling loads on the line. For a KTE-95D extruder running at 800 kg/h, the total heat removal requirement is approximately 120 to 150 kW, requiring a chiller with at least 180 kW nominal capacity (accounting for efficiency losses). Chillers should be specified with a closed-loop circuit, stainless steel heat exchanger, and a cooling tower or air-cooled condenser. For biodegradable lines, water temperature stability of +/- 1 degree Celsius is important for consistent barrel temperature control.

8.3 Cooling Tower

A cooling tower rejects heat from the chiller condenser and other water-cooled equipment. For a 1,000 kg/h biodegradable compound line, a cooling tower with 200 to 250 kW heat rejection capacity is typically required. The tower should be sized for the local ambient wet-bulb temperature and should include a water treatment system to prevent scale, corrosion, and biological growth in the cooling water circuit.

8.4 Air Compressor

Compressed air is required for pneumatic conveying, pneumatic valves, air-operated cylinders, and instrument air. A biodegradable compound line typically requires 5 to 10 cubic meters per minute of compressed air at 0.6 to 0.8 MPa. The compressor should be an oil-free type to prevent contamination of biodegradable pellets, and should include a refrigerated air dryer and particulate filter to deliver clean, dry air.

8.5 Vacuum System

The vacuum system for devolatilization includes a water-ring vacuum pump, a condensate separator, and a vacuum buffer tank. The pump capacity should be sized to handle the volatile load from the formulation. For PLA compounding with 3 to 5 percent volatile content, a vacuum pump with 100 to 200 cubic meters per hour displacement is typically adequate. The system should include a condensate collection pot with automatic drain to prevent liquid carryover into the pump.

8.6 Electrical and Control Systems

The line control system integrates all equipment into a unified control architecture. Kerke uses Siemens PLC hardware with a 15-inch touch screen HMI for operator interface. The control system manages extruder speed, barrel temperatures, feeder rates, vacuum pressure, pelletizer speed, and water system temperatures. Data logging and remote monitoring capabilities allow production engineers to track process parameters and diagnose issues remotely. The electrical panel should include phase protection, motor overload protection, and emergency stop circuits compliant with CE standards.

8.7 Dust Collection System

For lines processing powdered fillers or starch, a dust collection system is essential for worker safety and housekeeping. The system includes capture hoods at transfer points, ductwork, a cartridge dust collector with pulse-jet cleaning, and an exhaust fan. The dust collector should be rated for the specific dust type and must comply with local occupational health and safety regulations for airborne particulate exposure.

9. Equipment Selection Matrix by Annual Capacity

Selecting the right equipment configuration for a biodegradable compound production line depends primarily on the target annual production capacity. The following selection matrix maps common annual capacity targets to recommended Kerke extruder models, pelletizing systems, and approximate line configurations. This matrix assumes single-shift operation of 2,000 hours per year for the lower capacity range and three-shift operation of 6,000 hours per year for the higher capacity range.

The selection matrix above provides a starting point for equipment selection. Several additional factors influence the final configuration, including the specific biodegradable formulation, the number of product grades to be produced, the level of automation required, and the available factory infrastructure. For customers uncertain about the appropriate model, Kerke offers a laboratory twin-screw extruder (KTE-16B through KTE-35D) for formulation trials and process development, enabling data-driven scale-up to production-scale equipment.

For specialized applications such as starch-based biodegradable compounds with very high filler loadings (40 to 60 percent starch), a double-stage extrusion system using a KTE-series twin-screw extruder as the primary machine and an SE-series single-screw extruder as the secondary machine may be recommended. The twin-screw extruder handles intensive mixing and devolatilization, while the single-screw extruder provides stable pressure for pelletizing. This configuration is particularly effective for materials that tend to surging or vent flow in a single-stage extruder.

10. Applications in Biodegradable Plastic Compounding

The equipment list described in this article supports the full range of biodegradable plastic compounding applications. Each biodegradable polymer family has distinct processing characteristics that influence equipment selection, screw design, barrel temperature profiles, and pelletizing method. Understanding these application-specific requirements ensures that the production line is configured for optimal performance with the target material.

10.1 PLA (Polylactic Acid) Compounding

PLA is the most widely produced biodegradable polymer, derived from fermented plant starch. It is a crystalline thermoplastic with a melting point of 150 to 180 degrees Celsius and a glass transition temperature of 55 to 65 degrees Celsius. PLA compounding requires careful moisture control (below 250 ppm), moderate screw shear, and barrel temperatures of 170 to 200 degrees Celsius. Typical PLA compounds include PLA filled with talc for improved heat resistance, PLA blended with PBAT for improved toughness, and PLA with plasticizers for flexible film applications. The twin-screw extruder configuration for PLA typically uses a 40:1 L/D ratio with two vacuum vent ports for thorough devolatilization.

10.2 PBAT (Polybutylene Adipate Terephthalate) Compounding

PBAT is a flexible biodegradable copolymer used primarily as a blending component with PLA or starch to improve flexibility and toughness. PBAT has a melting point of 110 to 120 degrees Celsius and processes at relatively low temperatures (160 to 190 degrees Celsius). PBAT compounding lines benefit from a side feeder for introducing starch or calcium carbonate filler, and from a distributive mixing screw configuration with extended kneading zones. PBAT is less moisture-sensitive than PLA but should still be dried to below 500 ppm to prevent hydrolysis during processing.

10.3 PBS (Polybutylene Succinate) Compounding

PBS is a semi-crystalline biodegradable polyester with good heat resistance (heat deflection temperature of 90 to 95 degrees Celsius) and excellent processability. PBS compounds are used in agricultural films, compostable packaging, and disposable tableware. PBS processes at 180 to 210 degrees Celsius and requires moderate shear. For PBS compounds reinforced with natural fibers such as bamboo fiber or cellulose, a side feeder is essential for introducing the fiber into the melt without excessive fiber length reduction. The barrel temperature in the side feed zone should be lowered to prevent fiber charring.

10.4 Starch-Based Blends

Thermoplastic starch (TPS) is produced by gelatinizing native starch with a plasticizer (typically glycerol or sorbitol) in the extruder. TPS is then blended with PLA, PBAT, or PBS to produce biodegradable compounds with good processability and biodegradation rates. Starch processing requires a crammer feeder for the low-bulk-density starch powder, a liquid feeder for the plasticizer, and an extended devolatilization zone to remove water released during gelatinization. The screw configuration should include high-intensity kneading blocks in the gelatinization zone followed by reverse elements for melt sealing before the vent port.

10.5 PHA (Polyhydroxyalkanoate) Compounding

PHA is a family of biodegradable polyesters produced by bacterial fermentation. PHA compounds have a narrow processing window and are prone to thermal degradation above 180 degrees Celsius. PHA compounding requires gentle screw configurations with lower shear kneading blocks, shorter residence times, and lower barrel temperatures (150 to 175 degrees Celsius). The pelletizing system should use water ring or underwater cutting with cooled die plates to prevent pellet sticking, as PHA pellets can be tacky at temperatures above 40 degrees Celsius.

10.6 Biodegradable Masterbatch Production

In addition to direct compounding, the same equipment line can produce biodegradable masterbatches: concentrated pigment, filler, or additive dispersions in a biodegradable carrier resin. Masterbatch production requires higher shear mixing for pigment dispersion and finer filter screens (120 to 200 mesh) for gel removal. The screw configuration for masterbatch production typically uses more dispersive mixing elements and a longer L/D ratio (44:1 to 48:1) to ensure complete dispersion of high pigment loadings (40 to 60 percent).

11. Installation, Commissioning, and After-Sales Support

Procuring the equipment list is only the first step. Proper installation, commissioning, and ongoing support are equally critical to achieving stable production and maximizing return on investment. Kerke, backed by the Wanplas brand, provides comprehensive service and support designed to minimize ramp-up time and ensure long-term production reliability.

11.1 Pre-Shipment Testing

Every Kerke extruder undergoes a rigorous pre-shipment testing protocol before leaving the factory. The testing includes 72-hour continuous operation under simulated load conditions, verification of all barrel temperature zones, calibration of feeder accuracy, validation of vacuum system performance, and inspection of all safety interlocks. The customer is invited to witness the pre-shipment test, either in person or via remote video link. A detailed test report documenting all measured parameters is provided with the machine. This testing ensures that the equipment arrives at the customer site ready for installation without unexpected defects.

11.2 Installation and Commissioning

Kerke sends experienced engineers to the customer site for installation supervision and commissioning. The installation team assists with equipment positioning, utility connections (electrical, water, air), and integration of all line components. Commissioning includes dry-run testing, wet-run testing with the actual production formulation, parameter optimization, and production of initial sample pellets for quality verification. A typical commissioning period for a complete biodegradable compound line is 10 to 15 working days, depending on line complexity and site readiness.

11.3 Spare Parts Policy

Under the Wanplas brand promise, Kerke provides USD 500 free spare parts every year for each machine. This includes critical wear parts such as screw elements, barrel liners, O-rings, seals, and filter screens. Additionally, damaged parts within the warranty period are replaced free of charge. Kerke maintains a comprehensive spare parts inventory at its 19,997+ square meter factory, ensuring rapid dispatch of replacement parts to minimize production downtime. For customers in remote locations, Kerke recommends maintaining an on-site spare parts kit including spare screens, heating bands, thermocouples, and feeder screws.

11.4 Operator Training

Comprehensive operator training is provided during the commissioning period. Training covers machine operation, safety procedures, screw configuration changes, routine maintenance, troubleshooting, and quality control procedures. Training is tailored to the customer’s specific formulation and equipment configuration, ensuring that operators can independently manage day-to-day production. Kerke also provides detailed operation manuals, screw configuration diagrams, and maintenance schedules in both electronic and printed formats.

11.5 Remote Monitoring and Support

Kerke extruders are equipped with remote monitoring capabilities that allow factory engineers at the Kerke headquarters to access machine PLC data, review process parameters, and diagnose issues in real time. This remote support capability significantly reduces troubleshooting time for international customers, as many issues can be resolved without waiting for an engineer to travel to the site. Remote support is available through VPN-secured connections and is included as part of the standard after-sales service package.

11.6 Open Factory Visit Policy

As part of the Wanplas brand’s open factory policy, Kerke welcomes all prospective and existing customers to visit its manufacturing facility. Factory visits allow customers to inspect equipment quality firsthand, view machines under assembly and testing, discuss technical requirements with engineering staff, and witness trial runs with their specific formulations. The Kerke factory is located in Nanjing, China, with convenient access to international airports and high-speed rail connections. Visits can be arranged on short notice and are tailored to each customer’s specific interests and schedule.

12. Common Pitfalls and Troubleshooting Guide

Even with a well-designed equipment list, biodegradable compound production can encounter operational issues. The following table summarizes the most common pitfalls, their root causes, and recommended solutions. Understanding these issues in advance helps operators prevent defects and maintain consistent pellet quality.

12.1 Preventive Maintenance Schedule

A structured preventive maintenance program extends equipment life and prevents unplanned downtime. The following maintenance intervals are recommended for a biodegradable compound production line operating at 6,000 hours per year:

• Daily: Inspect feeder hoppers for bridging; verify barrel temperature setpoints; check vacuum pump water level; inspect pelletizer knives for wear; clean filter screens if pressure drop exceeds threshold.
• Weekly: Lubricate gearboxes per manufacturer specification; inspect and clean vacuum vent inserts; check all cooling water flow indicators; inspect pneumatic conveying filters; verify loss-in-weight feeder calibration.
• Monthly: Inspect screw elements for wear; check barrel liner condition with bore scope; test all safety interlocks; inspect electrical connections for loose terminals; replace air compressor filters.
• Quarterly: Change gearbox oil; inspect and replace wear rings on melt pump; calibrate all temperature sensors; inspect and clean cooling tower fill; perform vibration analysis on main motor and gearbox.
• Annually: Complete screw and barrel inspection; replace worn screw elements; inspect and rework die plate holes; overhaul or replace pelletizer knives; comprehensive PLC backup and software update.

Frequently Asked Questions

What L/D ratio is recommended for biodegradable plastic compounding?

For most biodegradable formulations including PLA and PBAT blends, an L/D ratio of 40:1 to 48:1 is recommended. This provides sufficient barrel length for complete melting, mixing, devolatilization, and venting without excessive thermal exposure. Shorter L/D ratios (32:1 to 36:1) can work for simple formulations with low filler content, but they limit the ability to incorporate multiple side feeds and vent ports. Longer L/D ratios (above 48:1) increase residence time and may cause thermal degradation in heat-sensitive biodegradable polymers.

Can the same twin-screw extruder process both PLA and PBAT?

Yes, the same KTE-series extruder can process both PLA and PBAT by changing the screw configuration and barrel temperature profile. However, a thorough purge cycle is required between material changeovers to prevent cross-contamination. The purge material should be a compatible biodegradable resin or a commercial purge compound. For operations requiring frequent material changes, a quick-release barrel design with clamp connections significantly reduces changeover time from hours to minutes.

Which pelletizing method works best for biodegradable plastics?

Underwater pelletizing and water-ring die face hot cutting are the most common choices for biodegradable compounds. Underwater pelletizing produces uniform spherical pellets with smooth surfaces, making it ideal for high-capacity lines and for materials that are tacky when cut. Water-ring cutting offers lower equipment cost and is suitable for medium-capacity lines producing 200 to 2,000 kg/h. For moisture-sensitive formulations where water contact is undesirable, air-cooled strand pelletizing is an alternative, though it requires more floor space and produces cylindrical rather than spherical pellets.

How much floor space does a complete biodegradable compounding line require?

Floor space depends on line capacity and configuration. A 500 kg/h line based on a KTE-75D extruder typically requires 200 to 300 square meters, while a 1,500 kg/h line based on a KTE-110D may need 400 to 600 square meters including raw material storage, utility equipment, and finished pellet storage areas. The space should include adequate clearance around the extruder for screw removal (typically 3 to 4 meters at the drive end), overhead clearance for feeder access (minimum 3 meters), and access aisles for maintenance and cleaning.

What moisture level is acceptable for biodegradable resin before feeding?

PLA should be dried to below 250 ppm (0.025 percent) moisture content before extrusion. PBAT is less sensitive but should still be below 500 ppm. PBS requires drying to below 300 ppm. Starch-based blends require drying to below 1,000 ppm to prevent foaming and hydrolytic degradation during extrusion. Exceeding these moisture thresholds causes hydrolytic chain scission, which reduces molecular weight and degrades mechanical properties irreversibly. The dehumidifying dryer should be monitored continuously, with dew point and drying temperature logged for quality traceability.

How often should screw elements be replaced on a twin-screw extruder?

Screw element replacement frequency depends on material abrasiveness and operating hours. For biodegradable compounds containing mineral fillers such as talc or calcium carbonate at 20 to 30 percent loading, inspect screw elements every 3,000 to 4,000 operating hours and replace worn elements every 8,000 to 12,000 hours. For unfilled PLA or PBAT compounds, screw elements can last 15,000 or more hours. Signs of wear include increased clearance between screw flight tips and barrel wall, reduced throughput at constant screw speed, and poor mixing quality. Kerke uses W6Mo5Cr4V2 high-speed tool steel with nitrided surfaces for standard elements, and offers tungsten carbide coated elements for highly abrasive applications.

Can Kerke provide a lab-scale extruder for formula development?

Yes, Kerke offers laboratory twin-screw extruders starting from KTE-16B designed for formula trials, material testing, and process development. These lab units replicate the processing behavior of production-scale extruders, enabling reliable scale-up. The lab extruders feature the same modular screw and barrel design as production models, allowing formulation work conducted on the lab machine to be directly transferred to the production line. Kerke also offers sample testing services at its factory, where customers can send their raw materials for trial compounding with full process parameter documentation.

What is the typical lead time for a complete biodegradable compounding line?

Standard configuration lead time is typically 60 to 90 days from deposit confirmation. Custom configurations with specialized barrel layouts, multiple side feeders, or automated material handling systems may require 90 to 120 days. Kerke provides a detailed project schedule after technical specification confirmation, including engineering design, manufacturing, pre-shipment testing, shipping, and installation timelines. For urgent projects, Kerke can sometimes offer expedited manufacturing by allocating additional production resources, subject to factory capacity.

Conclusion

Building a biodegradable plastic twin screw compound production line requires a comprehensive equipment list that spans seven major stages: raw material storage and drying, precision dosing and feeding, twin-screw extrusion, melt filtration, pelletizing, pellet cooling and conveying, and auxiliary utility systems. Each stage must be specified with careful attention to the unique processing characteristics of biodegradable polymers, including their moisture sensitivity, narrow thermal processing windows, and susceptibility to hydrolytic and thermal degradation. The equipment selection matrix provided in this article maps annual capacity targets to specific Kerke extruder models, from the KTE-50D for pilot-scale production to the KTE-135D for high-capacity industrial lines processing up to 2,500 kg/h.

Kerke, a Wanplas factory with 12+ years of specialized experience in twin-screw compounding extruders, 2,000+ machines installed across 70+ countries, and a 19,997+ square meter manufacturing facility, provides complete biodegradable compound production lines with full engineering support. From the KTE-16B laboratory extruder for formulation development to the KTE-135D production extruder with underwater pelletizing, every machine is backed by pre-shipment testing, on-site installation and commissioning, USD 500 free spare parts per year, comprehensive operator training, and remote monitoring support. The open factory policy welcomes you to visit the Kerke facility in Nanjing, China, to inspect equipment quality, discuss technical requirements with engineering staff, and witness trial runs with your specific biodegradable formulation.

If you are planning a biodegradable plastic compound production line, send your formulation details, target capacity, and product specifications to the Kerke engineering team for a tailored equipment configuration proposal. Whether you need a complete turnkey line or individual machines to upgrade your existing setup, Kerke and the Wanplas brand stand ready to support your project from concept to full production. We invite you to schedule a factory visit, request a sample trial run, or discuss your equipment list requirements with our technical specialists.