Petroquimica Triunfo Trithene CX 6369 is a medium density polyethylene supplied for extrusion blow molding, sheet extrusion, rotomolding after grinding, and compounding operations where environmental stress crack resistance and parison stability are required. Typical published nominal values place density at 0.936 g/cm³ when measured by ASTM D792 and melt mass-flow rate at 0.6 g/10 min under 190 °C/2.16 kg per ISO 1133-1:2022. These figures are nominal values, not batch guarantees. The grade is not formulated for high-gloss thin-wall injection molding; barrel residence times above 4 min at 240 °C can initiate oxidation and reduce environmental stress crack resistance.

In monolayer extrusion blow molding of UN-rated jerrycans intended for liquid agrochemicals, CX 6369 is processed on accumulator-head machines with extruder L/D of 24:1 to 30:1 and barrier screws having compression ratio between 2.5:1 and 3.0:1. Melt temperature at the die is maintained between 190 °C and 210 °C; head pressure of 25 MPa to 35 MPa is typical for a 20 L container and helps limit parison sag. The parison is programmed in 10 to 30 wall-thickness steps, with base weight increased for the pinch-off zone. Blow air pressure is set at 0.55 MPa to 0.80 MPa, mold cooling water at 10 °C to 25 °C, and demolding occurs when the internal surface reaches 70 °C or below. The resultant containers in the 5 L to 60 L range are tested under UN 6.1 and UN 8 packaging requirements including 1.2-m drop at -18 °C after conditioning, hydraulic pressure of 100 kPa for 30 min, and stack compression at 40 °C for 28 d. These tests are packaging-system certifications, not resin certifications; however, the grade contributes through ESCR values reported above 600 h under ASTM D1693 Condition B in the virgin state. Wetting agents, nonylphenol ethoxylates, and high-pH formulations reduce ESCR in service, and compatibility testing per ASTM D543 is required for each proprietary formulation before use.

What Limits Regrind Inclusion in Three-Layer Agrochemical Containers?

For coextruded containers where virgin CX 6369 forms the outer and inner layers and a barrier layer of EVOH or polyamide is separated by maleic anhydride grafted tie resins, the regrind stream is not returned to the inner layer when the product is a concentrated emulsifiable concentrate or solvent-based formulation. Regrind addition in the outer layer is limited to 15 wt% to 20 wt% of the total wall mass to preserve weld-line strength and UN drop performance. The layer distribution is typically 15/70/15 for outer/regrind-core/inner or 20/60/20 when no barrier layer is used. Die head temperatures are held at 195 °C to 205 °C because EVOH and PE coextrusion requires shear rates below 150 s⁻¹ to avoid interfacial instability. Melt pumps are used on each extruder; melt pressure variation is maintained within ±0.5 MPa to prevent layer-thickness drift. The final containers are used for solvent-based crop protection formulations, with barrier performance validated by weight loss at 40 °C for 28 d under transport classification tests and not by resin-level permeability alone.

Flat-die sheet extrusion for geomembrane liners uses CX 6369 only when carbon black is pre-dispersed. The grade is compounded with 2.0 wt% to 3.0 wt% carbon black masterbatch and 0.1 wt% to 0.3 wt% antioxidant package before entering a single-screw extruder with L/D 30:1 and screen pack of 60/80/100 mesh. Melt temperature is held at 220 °C to 230 °C, and the flat die is adjusted for a sheet thickness of 1.0 mm to 2.5 mm. Roll stack temperatures are kept between 70 °C and 90 °C to control surface oxidation and minimize residual stress. Geomembrane-grade material is qualified by ASTM D5397 single-point notched constant tensile load testing with 30% yield stress applied; accepted values for MDPE liners are typically above 300 h, though published data for this specific configuration is limited. Oxidative induction time is measured at 200 °C under oxygen per ASTM D3895; minimum values for buried liner applications are commonly specified at 100 min. Sheet is fabricated into smooth and textured geomembranes by calendering or coextrusion, then deployed in secondary containment for animal waste lagoons, mining heap leach pads, and irrigation ponds where low-temperature flexibility and stress crack resistance are required under ASTM D5747 chemical immersion.

Rotational Molding Powder Grind and Peak Internal Air Temperature

Although CX 6369 is supplied as pellet, rotational molding requires conversion to powder with a particle size distribution in which not more than 5% is retained on 35 mesh (500 µm) and not more than 10% passes 100 mesh (149 µm). Grinding is performed on high-speed attrition mills with liquid nitrogen cooling; powder bulk density after grinding is typically 0.36 g/cm³ to 0.40 g/cm³. In biaxial machines, the mold is charged to give a wall thickness of 3 mm to 12 mm, and the peak internal air temperature is controlled at 205 °C to 220 °C. Higher internal air temperature above 232 °C causes surface oxidation and pore formation at the inner wall. Rotational speed ratio is set at 4:1 for cylindrical tanks and altered to 1:4 for conical tanks; cycle time for a 5 mm wall tank is typically 18 min to 25 min. Cooling begins with forced air for 5 min to 10 min, followed by water mist until the internal air temperature falls below 80 °C. The resulting storage tanks are tested per ASTM D1998 for stationary polyethylene tanks and are used for water, mild acids, and agricultural adjuvants at atmospheric pressure.

When CX 6369 is Thermoformed into Returnable Transit Sheets and Material-Handling Trays

Extruded sheet from CX 6369 can be reheated and vacuum-formed into dunnage trays and returnable pallet covers where the part thickness remains above 1.2 mm. Sheet surface temperature before forming is maintained between 150 °C and 165 °C; below 145 °C the sheet exhibits elastic recovery that prevents corner replication, and above 170 °C the extruded sheet loses sag resistance and tears during plug assist. Mold temperature is controlled at 40 °C to 60 °C with aluminum tooling. Vacuum of -0.08 MPa is applied for 5 s to 10 s, followed by positive air ejection at 0.2 MPa. The formed parts are used in automotive component transport and industrial material handling where repeated cleaning with alkaline detergents is required; environmental stress crack resistance under ASTM D1693 Condition C is the governing property, with F50 values above 600 h in virgin material. With no UV stabilizer, outdoor service is limited to 6 months to 12 months before embrittlement.

Automotive windshield washer reservoir blow molding from CX 6369 uses accumulator-head machines with shot capacity of 1.5 L to 5 L. Melt temperature at the head is maintained at 200 °C to 215 °C, and clamp force on the molds is set between 400 kN and 800 kN depending on projected area. The reservoirs are designed with pinch-off flash and a wall thickness of 2.0 mm to 3.0 mm; low-temperature drop tests at -30 °C require notched Izod impact values above 20 kJ/m² per ISO 180/1A, which the unfilled MDPE typically exceeds when processed without moisture. Pre-drying is not required unless storage humidity exceeds 60% RH for more than 48 h, in which case surface condensation can produce micro-voids and weld-line weakness. The reservoirs are filled with methanol/water mixtures and tested for stress cracking for 200 h at 60 °C under internal strain of 0.5%. Compatibility with glycol-based coolants is limited, and these reservoirs are not specified for pressurized coolant expansion tanks where temperatures exceed 90 °C continuously.