Modified Plastic Extrusion Process: How to Enhance Material Performance Through Equipment

Modified plastics can significantly improve the mechanical properties (strength, toughness), thermal stability, weather resistance, etc., of base resins by adding fillers, tougheners, flame retardants and other additives, or adopting blending and compounding methods. As the core of modified processing, extrusion equipment directly determines the modification effect through its structural design, parameter configuration and functional optimization. The following starts from the key systems of equipment to analyze how to improve material performance through equipment design:

I. Core Requirements: Performance Improvement Goals for Modified Plastics

Modified processes need to specifically address the shortcomings of base resins. Typical requirements include:

• Mechanical reinforcement: Improving tensile strength (e.g., PP from 30MPa to 80MPa) and rigidity (flexural modulus from 1500MPa to 5000MPa) through filling with glass fibers, carbon fibers, etc.;

• Toughness improvement: Adding elastomers (e.g., EPDM, POE) to increase the impact strength of materials by 3-5 times (e.g., PS notched impact from 2kJ/m² to 10kJ/m²);

• Functional enhancement: Achieving flame retardancy (UL94 V0 grade), heat resistance  (long-term service temperature from 80°C to 150°C), conductivity (volume resistivity from 10¹⁴Ω·cm to 10³Ω·cm), etc.

II. Impact and Optimization of Core Systems of Extrusion Equipment on Performance

(1) Screw System: Determines Mixing Dispersion and Shear Strength

The screw is the "heart" of modified extrusion. Its length-to-diameter ratio (L/D), screw element combination, and shear strength directly affect the uniformity of additive dispersion and the integrity of material structure.

1. Selection of Length-to-Diameter Ratio (L/D)

• Basic blending modification (e.g., PP+POE toughening): L/D=30-36, meeting the initial dispersion of additives;

• High-fill modification (e.g., PP+50% calcium carbonate): L/D=40-48, extending material residence time to ensure full infiltration of fillers;

• Precision functional modification (e.g., flame-retardant ABS): L/D=52-60, adapting to multi-stage feeding and stepwise reactions (e.g., flame retardant coating).

2. Design of Screw Element Combination

• Reinforcement modification (glass fiber/carbon fiber filling):
        A combination of "strong conveying + medium shear" is required: deep groove conveying elements in the feeding section, medium shear kneading blocks (stagger angle 45°) in the melting section to avoid       excessive fiber breakage (retaining length ≥0.2mm to ensure strength); reverse thread elements are added in the dispersion section to force material backflow and mixing.

• Toughening modification (elastomer blending):
        A combination of "weak shear + strong dispersion" is required: shallow groove conveying elements are used to reduce shear heat, and wide-gap kneading blocks (thickness 20mm) are used to achieve uniform       dispersion of elastomer particles (particle size controlled at 1-3μm to avoid agglomeration).

• Nanomodification (e.g., nano-montmorillonite filling):
        "High shear + high-frequency dispersion" is required: toothed disc elements are configured to peel off nano-layers through high-frequency shear (peeling degree ≥90%), and triangular prism mixing elements in the dispersion section are used to achieve uniform distribution of nano-phases.

(2) Feeding System: Ensuring Precision and Stability of Component Proportions

A proportion deviation of additives and resins (even ±0.5%) can lead to performance fluctuations (e.g., insufficient flame retardants can reduce the flame retardant grade from V0 to V2), which needs to be controlled by precision feeding equipment:

1. Loss-in-Weight Feeder

• Application scenario: Multi-component modification (e.g., more than 3 additives) with a metering accuracy of ±0.1%;

• Advantage: Real-time feedback of material weight changes, automatically adjusting screw speed to compensate for errors (e.g., immediately adjusting host speed when glass fiber feeding fluctuates).

2. Side Feeding Device

• High-fill modification (e.g., PE+60% talc): Twin-screw side feeding (linked with host speed) is used to avoid agglomeration of main materials and fillers at the feed port;

• Heat-sensitive additives (e.g., antioxidants): Added in the later stage of the melting section through side feeding to reduce high-temperature degradation (retention rate increased by 20%-30%).

(3) Temperature Control System: Precisely Controlling Melting and Reaction Temperatures

Temperature deviations (±5°C) may cause material degradation (e.g., PA6 is prone to chain scission above 280°C) or poor plasticization (affecting additive dispersion), requiring hierarchical temperature control and dynamic adjustment:

1. Segmented Heating and Cooling

• Feeding section: Low temperature (slightly 5-10°C higher than the resin melting point) to prevent premature melting and agglomeration (e.g., PP feeding section temperature 170-180°C);

• Melting section: Medium temperature (resin melting point +20-30°C) to ensure complete melting (e.g., PC melting section 280-300°C);

• Dispersion section: High temperature (adjusted according to additive activity, e.g., brominated flame retardants need 200-220°C for activation), but not exceeding the material decomposition temperature.

2. Dynamic Temperature Control Technology

• Equipped with an infrared thermometer to monitor melt temperature in real-time, linked with PLC to adjust heating power (response speed ≤1s);

• Independent water cooling systems are installed in high-shear areas (e.g., at kneading blocks) to avoid material discoloration caused by local overheating (e.g., ABS yellowing).

(4) Venting System: Removing Volatiles to Improve Material Compactness

Moisture in raw materials (e.g., PA6 with moisture content >0.2% will cause product bubbles) and additive decomposition products (e.g., plasticizer volatiles) need to be discharged through the venting system:

1. Multi-stage Venting Design

• Primary venting (vacuum degree -0.06MPa): Located after the melting section to remove surface moisture and air from raw materials;

• Deep venting (vacuum degree -0.09MPa): Located in the dispersion section to discharge small molecules generated by additive reactions (e.g., HCl decomposed from flame retardants);

• Application scenario: Hygroscopic materials (PA, PBT) require more than 3 stages of venting, which can reduce moisture content to below 0.05%.

2. Anti-material Emission Structure

• A reverse spiral element is installed at the vent port to prevent molten materials from being       sucked into the vacuum system, ensuring venting efficiency (volatile removal rate ≥95%).

(5) Die and Mold: Controlling Melt Uniformity and Molding Stability

Fluctuations in die pressure (±5bar) can lead to uneven density of extrudates, affecting subsequent pelletizing and product performance:

1. Melt Pump (Gear Pump)

• Installed before the die to stabilize melt pressure (fluctuation ≤±1bar), especially suitable for high-fill materials (e.g., PP+40% glass fiber) to avoid uneven extrusion caused by material viscosity fluctuations.

2. Static Mixer

• Placed in the die, through multi-layer splitting and merging, the melt temperature and component distribution deviation are ≤2% (e.g., in masterbatch modification, ensuring color difference ΔE ≤1).

III. Equipment Configuration Schemes for Typical Modification Scenarios

1. Glass Fiber Reinforced PP (for automotive bumpers)

• Equipment: Twin-screw extruder (L/D=48, screw diameter 65mm) + loss-in-weight feeding (dual paths for resin + glass fiber) + 3-stage venting + melt pump;

• Key parameters: Screw speed 300-350rpm, glass fiber side feeding position in the middle of the melting section (retained length 0.3-0.5mm), venting vacuum degree -0.08MPa;

• Performance improvement: Tensile strength from 32MPa→85MPa, flexural modulus from 1800MPa→5500MPa.

2. POE Toughened PP (for food packaging films)

• Equipment: Twin-screw extruder (L/D=36) + low-shear screw combination (45° kneading blocks account for ≤30%) + static mixer;

• Key parameters: Host speed 200rpm (shear rate ≤1000s⁻¹), POE side feeding in the later melting stage (dispersion particle size 1-2μm);

• Performance improvement: Notched impact strength from 4kJ/m²→25kJ/m², elongation at break from 10%→300%.

3. Flame-Retardant ABS (for electronic enclosures)

• Equipment: Twin-screw extruder (L/D=52) + 4-stage feeding (resin + brominated flame retardant + synergist + antioxidant) + deep venting (vacuum degree -0.095MPa);

• Key parameters: Dispersion section temperature 220°C (activating flame retardants), screw speed 400rpm (ensuring uniform coating of flame retardants);

• Performance improvement: Flame retardant grade from UL94 HB→V0, heat distortion temperature from 85°C→105°C.

IV. Core Directions for Equipment Optimization

1. Intelligent control: Realize automatic adjustment of process parameters through online detection (e.g., near-infrared spectroscopy for real-time component analysis, melt flow rate meter for viscosity monitoring) (e.g., real-time compensation by feeders when additive dosage deviates);

2. Modular design: Screw elements and barrels can be quickly replaced (within 30 minutes) to adapt to multi-variety modification needs (e.g., switching from reinforcement modification to flame retardant modification);

3. Energy-saving transformation: Adopting servo motors (energy consumption reduced by 30%) and electromagnetic heating (thermal efficiency up to 90%) to reduce the negative impact of high temperatures on material performance.

Through equipment structure optimization and precise control of process parameters, modified plastics can maximize performance breakthroughs while maintaining processing stability, meeting the stringent requirements of high-end fields (automotive, electronics, new energy) for materials.