Does impurity in plastic granules affect product quality?
Publish Time: 2025-10-29
Plastic granules, as a fundamental raw material in modern manufacturing, are widely used in various molding processes such as injection molding, extrusion, and blow molding. Their purity directly determines the performance and appearance of the final product. Even trace amounts of impurities during production can have a profound impact on product quality. These impurities may originate from residual catalysts during raw material synthesis, foreign matter in recycled materials, contamination during transportation and storage, or mechanical wear during granulation. They exist as metal scraps, dust, charred material, different types of plastic granules, or unreacted polymers. While seemingly insignificant, they can trigger a series of chain reactions during processing and use.
First, the impact of impurities on the appearance of the product is most obvious. In transparent or light-colored products, even tiny black spots, color differences, or cloudy patches can severely affect the visual effect and lower the product's grade. For products requiring high surface finish, such as appliance casings or optical components, impurities can cause surface depressions, pitting, or flow marks, disrupting the perfect replication of the mold cavity. In film or sheet production, impurities can cause perforations or uneven thickness, leading to reduced material strength or poor printing.
A deeper impact manifests in the material's physical and mechanical properties. Hard impurities such as metal particles or sand can scratch the inner walls of the extruder screw or injection nozzle, accelerating mechanical wear and increasing maintenance costs. Once in the mold, these particles can clog microchannels or vents, causing incomplete filling, trapped air, or localized stress concentration. When impurities are present inside the product, they become stress concentration points, easily triggering crack propagation under external forces, reducing the product's impact resistance, tensile strength, and fatigue resistance. For components subjected to pressure or frequent bending, this defect can lead to sudden failure during use, posing safety hazards.
In electrical insulation or food contact applications, the effects of impurities are even more sensitive. Conductive impurities can damage the insulating properties of plastics, causing short circuits or leakage in electronic components, affecting the safe operation of equipment. The mixing of non-food grade materials into food packaging plastics may release harmful substances, threatening human health. Furthermore, certain chemical impurities may decompose during high-temperature processing, releasing corrosive gases that damage the mold surface, or react with the main material, altering its rheological properties and causing processing difficulties.
Impurities can also interfere with subsequent processing and functional realization. In products requiring secondary processing such as spraying, electroplating, or bonding, surface or near-surface impurities can disrupt interfacial adhesion, leading to coating peeling or adhesive failure. For functional plastics, such as materials with added flame retardants, antistatic agents, or antibacterial agents, impurities may adsorb or destroy these additives, preventing them from dispersing evenly or functioning properly, resulting in substandard product functionality.
To mitigate the risks posed by impurities, raw material suppliers typically conduct rigorous screening and testing of plastic granules, employing techniques such as magnetic separation, sieving, air separation, and optical sorting to remove foreign matter. Users should also ensure a clean storage environment before use, avoiding exposure of particles to dust or humid air. For high-requirement products, pre-filtration or the use of injection molding machines with screens can further intercept impurities. In the use of recycled materials, impurity control is particularly critical, requiring the establishment of a comprehensive sorting and cleaning process to ensure the purity of the recycled materials.
Ultimately, the purity of plastic granules is the cornerstone of ensuring product quality. It not only concerns the product's appearance and performance but also affects production efficiency, equipment lifespan, and end-product safety. From source control to process management, vigilance against impurities is essential at every stage to ensure the final product meets the expected quality standards.
