Why Is It Difficult For An Extruder To Handle All Materials? ——In Depth Analysis Of The Game Between Strong And Weak Shear in Twin-screw Extruders
In 2026, as environmental regulations become increasingly stringent and new materials emerge constantly, the global plastic industry is undergoing a profound "materials revolution". From the dry solid-state battery process recently announced by BMW Group to the high-value utilization of PCR consumer recycled materials globally, the co rotating twin screw extruder, as the core equipment for plastic granulation, is losing its "universal" halo. Data shows that the global revenue scale of twin screw extruders has reached 11.11 billion yuan in 2024, but the challenge that comes with it is: why cannot the same equipment perfectly handle all materials from glass fiber reinforcement to biodegradation? The answer lies in the subtle balance between strong and weak cuts.
1. Strong and weak shearing: the "double-edged sword" effect of efficient extruders
In the field of plastic extrusion granulation, co rotating twin screw extruders are considered the most tolerant equipment due to their flexible modular design and excellent mixing performance. However, tolerance does not mean omnipotence. The shear strength of the equipment directly determines the "plasticization fate" of the material.
1.1 Core Contradiction: The Game of Dispersion and Degradation
In today's pursuit of high output and high performance, efficient extruders face a fundamental physical contradiction: how to achieve ultimate dispersion without destroying the nature of the material?
1.2 Strong Shear: A Powerful Tool for Fiberglass Reinforcement
For modified plastics that require fiber reinforcement, strong shear is necessary. The high-strength shear force brought by high rotation speed can fine the glass fiber and evenly disperse it in the resin matrix. But too much is not enough: when the shear is too strong and the glass fiber retention length is too short, its mechanical reinforcement effect is greatly reduced.
Key Q: Why do downstream customers always say that the strength of the product is not enough when I make materials containing fiberglass?
A: The problem is likely to lie in the matching of screw speed and shear configuration. Excessive shearing may make the fiberglass appear evenly dispersed, but in reality, it excessively shatters the fiberglass. When processing reinforced plastics with co rotating twin screw extruders, a "weak shear transition section" must be designed to ensure dispersion while retaining the effective length of the fiberglass.
1.3 Weak Shear: A "hotbed" for high filling and thermosensitive materials
When dealing with high filling calcium carbonate (such as the recent case of Bahrain Pipeline Company, which filled up to 65 parts) or heat sensitive materials (such as PVC, biodegradable materials), weak shear becomes mainstream. Excessive shear force can cause local friction overheating, leading to material thermal degradation, yellowing or performance deterioration.
In a study released by BMW Group in March 2026, it was pointed out that precise control of the shear force of the twin screw is necessary when preparing the positive electrode of sulfide solid-state batteries: low-temperature weak shear can maintain particle integrity, while strong shear can promote the formation of fibers in the binder, but excessive shear force can crush the active material particles, leading to a decrease in battery performance.
2. The "Butterfly Effect" of RPM: A Chain Reaction from Yield to Quality
The screw speed is not only a regulating valve for production capacity, but also a core variable that affects the internal stress of materials. According to the latest industry technology white paper, the setting of rotational speed must form a synergistic relationship with the feeding amount, known as "hunger feeding".
2.1 High speed: Efficiency and risk coexist
·Data support: According to the classic formula for extrusion temperature rise, the temperature rise of the melt (Δ T) ≈ the change in die pressure (Δ P) ÷ 2. When blindly increasing the rotational speed in pursuit of output leads to a 40bar increase in die pressure, the melt temperature may unexpectedly soar by 20 ℃. This 20 ℃ is sufficient to cause molecular chain breakage in certain metallocene polyethylene or biobased plastics.
·Current affairs link: The current global pursuit of "lightweight" and "thin-walled" packaging, such as the processing of yogurt cup recycled materials (PCR). This type of material has a low packing density (which can be as low as 30g/L). Although high-speed rotation can increase the conveying capacity, if the shear fit is not appropriate, it can easily cause the material to stay in the barrel for too short a time, mix unevenly, and ultimately affect the mechanical properties of the regenerated particles.
2.2 Low speed: Balance between dwell time and energy consumption
Low speed means longer material residence time, which is beneficial for the gentle plasticization of thermosensitive materials. However, for applications that require efficient devolatilization (removal of moisture and monomers), such as recycling complex multilayer composite films (PE/EVOH), excessively low rotational speeds can lead to slow surface renewal rates and greatly reduce devolatilization efficiency.
Key Q&A: I want to try making a new ingredient (such as plant-based protein meat or biodegradable material), but I always can't do it well with the existing old process parameters. Why?
A: The rheological properties of each new material are unique. A recent study by Jiangnan University showed that for the special material of plant protein meat, the optimized twin screw structure (thread width, lead combination) can significantly increase the mixing coefficient by 17.1%. This indicates that there is no "universal" fixed parameter, only by customizing a "strong/weak shear combination" co rotating twin screw extruder based on material characteristics can high cost-effective granulation be achieved.
3. Industry Outlook: How do we define a "good" plastic extruder in 2026?
Faced with the trend of the global twin screw extruder market moving towards high efficiency, energy saving, and intelligent control in 2026 (expected to reach 12.92 billion yuan in 2031), customers (especially international customers who are new to it) should establish a new product selection logic.
3.1 Abandon the obsession with "omnipotence" and embrace "modularity"
The core value of an efficient extruder lies not in what it can do, but in how quickly and cost effectively it can adjust why it can do anything when changing materials.
·The magic of screw combination: By replacing different kneading block components and threaded components, the local shear rate and reflux rate can be changed. For example, wide edged threaded blocks are used for pressure building and conveying, while narrow kneading blocks are used for strong shear dispersion.
·Application example: In the technology showcased at EREMA K 2025, by coupling the preprocessing unit with twin screw, even thin-walled packaging waste with greatly fluctuating packing density can be homogenized with high impurity content by adjusting the screw speed and shear configuration.
3.2 Data driven process replication
For customers who pursue high cost-effectiveness, especially new material developers, the repeatability of equipment is crucial.
Nanjing Kelongwell Chemical Machinery Co., Ltd. emphasized in its design that it is necessary to strategically manage melt pressure. By installing precise pressure sensors on the extruder barrel to monitor the pressure gradient from feeding to the die, the viscosity changes and mixing state of the material can be inferred in reverse. This means that once the perfect weak shear "golden speed" and temperature curve are found for customer A's biodegradable plastic, this formula can be replicated without damage in large-scale production.
Conclusion: Suggestions for Global Explorers
In the wave of transition from the plastic industry to a circular economy, the co rotating twin screw extruder is no longer a simple melt extrusion tool, but a "microstructure processing plant" for polymer materials.
Whether dealing with high glass fiber reinforced engineering plastics, environmentally friendly recycled materials with high filling and low packing density, or trying new plant-based materials, the key to success lies in a deep understanding of what your materials want.
·Is it afraid of heat? Choose a plastic extruder solution with weak shear, large volume, and low temperature rise control.
·Does it require strength? Design a screw configuration that combines strong shear and relaxation.
·Is it an unknown new material? Looking for partners like Nanjing Kelongwell Chemical Machinery Co., Ltd. who can provide modular design and support fine adjustment of process parameters.
In the world of extruders, true professionalism is not about manufacturing a machine that can handle all materials, but about creating a platform that maximizes the potential of materials.
