In the recycled plastics commodity market, not all PET flakes are valued equally. The pricing hierarchy is strictly dictated by downstream application requirements. At the upper echelon of mechanical recycling sits the production of fiber grade rPET flakes. These materials are not destined for low-tier packaging strapping or thick injection molding; they are engineered for the chemical spinning of Polyester Staple Fiber (PSF) or continuous filament yarns.

Lorsque les fabricants de textiles extrudent la fusion de polymère à travers des filières microscopiques (souvent de moins de 0,3 mm de diamètre), les tolérances physiques et chimiques sont pratiquement nulles. Toute déviation dans l'intégrité du polymère entraîne des filaments cassés, un blocage rapide des filtres de fusion et des temps d'arrêt de production coûteux. Par conséquent, les normes de qualité des flocons rPET ne sont pas subjectives ; elles sont définies par des limites rigides et mesurables sur des contaminants spécifiques.

Les trois indicateurs de qualité non négociables

To classify as fiber grade rPET flakes, the output from a washing line must typically pass strict laboratory analysis focusing on three primary failure points:

1. The Thermal Threat: PVC Contamination (< 50 PPM) Polyvinyl Chloride (PVC) is the absolute enemy of polyester spinning. Because PVC and PET have similar melting points but vastly different thermal degradation profiles, any PVC present in the extruder will burn and release hydrochloric acid. This acid acts as a catalyst, aggressively degrading the PET molecular chain, turning the melt brown, and severely reducing its intrinsic viscosity (IV). Controlling PVC content in PET flakes requires rigorous upstream intervention. It cannot be washed away; it must be physically removed through manual sorting or optical separation before the material ever enters the heavy-duty PET crusher.

2. The Chemical Residue: pH Level (< 8) Heavy-duty cleaning requires aggressive saponification. High-capacity recycling lines utilize caustic soda (NaOH) in a hot wash PET line to dissolve organic oils and stubborn adhesives. However, if this highly alkaline solution remains on the plastic, it will cause chemical hydrolysis during downstream melting. To achieve fiber grade, the pH value of the final flake must be neutralized to below 8. This is mechanically achieved through aggressive scouring inside high-speed friction washers, followed by multi-stage deep-water rinsing tanks that dilute and isolate the chemical carryover.

3. The Physical Barrier: Moisture Content (< 1%) PET is a hygroscopic material, meaning it absorbs water. If the moisture content exceeds 1% (or even 0.5% for ultra-fine filaments), the water molecules will react with the PET polymer chains at extrusion temperatures (around 280°C). This thermal hydrolysis sharply drops the molecular weight, resulting in brittle fibers that break under tension.

Configurations mécaniques pour le contrôle de l'humidité

Faire descendre les niveaux d'humidité d'un processus de lavage complètement submergé à moins de 1 % nécessite une infrastructure de séchage spécialisée. Compter sur l'évaporation ambiante est impossible dans un cadre industriel.

Based on Shuliy Group’s engineering configurations, the initial stage utilizes a centrifugal dryer (operating with a 37kw motor for 3000kg/h capacities). The intense G-force generated by the rotor strips away up to 98% of the surface water. However, to guarantee the strict parameter required for fiber grade rPET flakes, the material must then be transported through a thermal drying pipeline. Injecting hot air (typically through a 15-to-20-meter pipe system) evaporates the remaining microscopic moisture trapped within the flake crevices.

Ultimately, producing fiber-grade material is not about having machines à laver that clean plastic. It is about operating a synchronized chemical and mechanical system designed to strictly control PVC parts-per-million, neutralize pH, and eradicate moisture.