Do modified particles affect material flowability during injection molding or extrusion?
Publish Time: 2025-08-26
Injection molding and extrusion are two of the most widely used techniques for producing plastic products. Their molding quality and production efficiency are highly dependent on material flowability. Flowability determines whether the molten plastic can smoothly fill the mold cavity or flow through complex flow channels, directly impacting the integrity, surface finish, and internal stress distribution of the product. When using modified particles as raw materials, their impact on material flowability becomes a key consideration in process control. Modified particles impart specific properties to plastics by adding fillers, reinforcing fibers, flame retardants, toughening agents, or functional additives. However, the introduction of these ingredients often significantly affects the original rheological properties.The impact of modified particles on flowability depends primarily on their internal formulation and component properties. Certain additives, such as high proportions of inorganic fillers such as calcium carbonate, talc, or wollastonite, increase melt viscosity in the molten state, making the material "thick" and reducing flowability. This is because friction between the filler particles and the polymer molecular chains restricts the free movement of the molecules. Especially at high fill ratios, the melt's shear sensitivity increases, creating more significant resistance at low flow speeds, potentially leading to defects such as underfill, flow marks, or noticeable weld lines. Conversely, the addition of certain lubricating additives or processing modifiers can improve flowability by forming a lubricating layer between molecules, reducing internal friction and allowing the melt to flow more easily.Reinforcement fiber-modified particles, such as glass fiber or carbon fiber, have a particularly significant impact on flowability. Fibers are distributed in the melt as long strands and tend to align in the direction of flow, creating a "fiber bundle" effect and increasing the anisotropy of the melt. Fibers can accumulate in mold corners or thin-walled areas, obstructing melt flow and causing localized filling difficulties. While the presence of fibers significantly increases melt strength, it also increases injection pressure requirements, placing higher demands on equipment power and mold sealing. Therefore, when designing products using glass fiber-reinforced materials, it is important to optimize gate location, runner dimensions, and injection parameters to accommodate their lower flowability.On the other hand, while some toughening agents or elastomer-modified particles are intended to improve the material's impact resistance, their amorphous structure or low glass transition temperature can cause excessive softening at high temperatures, resulting in reduced melt strength, drooping, flashing, or dimensional instability. These materials can also experience melt fracture or surface roughness during extrusion, requiring control through adjustments to the temperature profile and pull-off speed.To balance performance and processability, rheological optimization is often performed during the manufacturing process of modified particles. By selecting a compatible carrier resin, controlling the particle size and surface treatment of the additives, and adding internal lubricants, the modified particles can achieve the desired performance while minimizing negative impacts on the base material's flow properties. For example, treating fillers with silane coupling agents can improve interfacial bonding with the plastic matrix, reduce agglomeration, and enhance dispersion uniformity, thereby mitigating viscosity increases. Furthermore, the pelletizing process for the modified particles is crucial. Uniform particle morphology and stable density ensure stable feeding in the injection molding machine or extruder, avoiding melt inhomogeneities caused by feed fluctuations.In actual applications, processors need to adjust process parameters based on the characteristics of the modified particles used. Appropriately increasing barrel temperature, injection pressure, or screw speed can compensate for fluidity loss to a certain extent. Furthermore, mold design should consider smooth flow path transitions, avoid sharp turns, and provide a well-designed venting system to address potential venting issues associated with modified materials.In summary, modified particles can indeed affect material flowability during injection molding or extrusion. This impact can be negative, controllable, or even optimized. The key lies in understanding the rheological behavior of the modified component and achieving an optimal balance between performance and processability through coordinated adjustments in formulation design, pelletizing technology, and processing parameters.
