Polycomp RC 14/4 HS UV2 PP Copolymer is a reactor-grade polypropylene impact copolymer compound formulated for injection-molded exterior and semi-structural components. The nomenclature is interpreted as follows: RC denotes the reactor copolymer backbone; 14/4 identifies a nominal melt flow rate of 14 g/10 min at 230 °C under a 2.16 kg piston load per ISO 1133-1, with approximately 4 wt% ethylene comonomer; HS indicates a high-stiffness formulation; and UV2 identifies a dual ultraviolet stabilization package combining a high-molecular-weight hindered amine light stabilizer and a benzotriazole-class UV absorber. Because the manufacturer’s full lot-specific data sheet is not reproduced in this introduction, quantitative values are presented as representative ranges for a UV2-stabilized high-stiffness PP impact copolymer and must be verified against the current certificate of analysis before tooling release or part qualification. The material is typically supplied as natural or pre-colored cylindrical pellets and is processed on conventional reciprocating-screw injection molding machines with melt temperatures not exceeding 260 °C.

How Does the UV2 Stabilizer Package Alter Outdoor Weathering Retention?

Accelerated weathering response for dual-stabilized PP impact copolymers of this class is evaluated under ISO 4892-2 Method A using xenon-arc exposure, daylight filters, an irradiance of 0.51 W/m² at 340 nm, and a black-standard temperature of 65 °C. Automotive exterior programs commonly apply SAE J2527 with extended humidity cycles. The UV2 package retards chain scission and surface micro-cracking through the combination of radical scavenging by the hindered amine component and competitive absorption in the 300 nm to 360 nm range. Representative compounds exhibit tensile strength retention of 75% to 85% and 60° gloss retention above 60% after 1500 h to 2000 h of xenon-arc exposure, depending on pigmentation and surface texture. Single-package UV absorber impact copolymers may lose 20% to 30% of tensile strength over the same interval. Stabilizer migration is low in comparable systems; extraction loss below 0.1% by mass after 100 h in 80 °C water is typical. Dark brown or black parts require additional validation because elevated part-surface temperature under solar load can increase antioxidant consumption and reduce gloss retention. Published data for this specific commercial configuration is limited; production-color weathering plaques should always be used for final approval.

Mechanical differentiation against general-purpose PP impact copolymers is driven by the high-stiffness package. Under ISO 527-2 Type 1A tensile testing at 23 °C and 50 mm/min, a representative RC 14/4 HS UV2 compound exhibits a secant tensile modulus of approximately 1800 MPa to 2000 MPa, while an unfilled PP impact copolymer of similar melt flow rate ranges from 1100 MPa to 1300 MPa. Tensile yield stress is typically 29 MPa to 32 MPa, with elongation at yield from 5% to 7%. Notched Charpy impact at 23 °C under ISO 179-1/1eA is approximately 8 kJ/m² to 12 kJ/m², and at -20 °C approximately 3.5 kJ/m² to 5 kJ/m². The property position is therefore between an unfilled PP impact copolymer and a 20 wt% talc-filled PP homopolymer, with lower density and reduced anisotropic shrinkage than the mineral-filled alternative.

Melt Rheology and Hot-Runner Pressure Demand

Flow behavior is governed by the nominal 14 g/10 min melt flow rate. Capillary rheometry on comparable reactor-grade impact copolymers yields an apparent shear viscosity of 180 Pa·s to 220 Pa·s at 1000 s⁻¹ and 230 °C. The melt is pseudoplastic, with a power-law index over 100 s⁻¹ to 5000 s⁻¹ ranging from 0.32 to 0.38. Hot-runner pressure demand increases when runner diameters fall below 6 mm or when multiple drops exceed the plasticating capacity of the molding machine. Production-scale processing on a 25:1 L/D general-purpose screw is typically stable with back pressure from 5 MPa to 10 MPa and screw speed from 50 rpm to 120 rpm. Barrel set points from feed to nozzle are commonly 200 °C, 220 °C, 230 °C, and 240 °C, with the nozzle held at 250 °C maximum. Melt temperature must not exceed 260 °C; residence time at full temperature should remain below 5 min to avoid yellowing and UV additive degradation. Shut-down purging with a low-MFR polypropylene or a commercial purging compound is recommended when the previous material contains acetal or polyamide residues.

Low-temperature impact retention and mold shrinkage interact directly in tool design. Prototype plaques molded to ISO 294-4 exhibit parallel shrinkage of 1.2% to 1.5% and perpendicular shrinkage of 1.3% to 1.6%. This range is higher than a PP homopolymer and lower than many unfilled PP impact copolymers. Gate freeze time is estimated at 2 s to 4 s for a 2.5 mm wall section, and packing pressure of 40 MPa to 60 MPa is generally required to control sink marks. Mold temperature should be maintained between 20 °C and 50 °C; higher mold temperatures improve surface gloss and weld-line strength but extend cycle time. Weld-line strength is direction-sensitive in high-stiffness impact copolymers and should be validated on tensile specimens cut across the weld plane using ISO 527-2 before accepting gate placement. Textured surfaces may require draft angles at least 1° greater than those used for unfilled homopolymer grades to avoid ejection drag.

When Ambient Humidity Exceeds 60% During Storage or Conveying

Polypropylene copolymers are not hygroscopic in the manner of polyamides, but surface moisture from humid air can produce splay, haze, and shot-weight variation. When the material is stored or conveyed in an environment above 60% relative humidity, pre-drying is required at 80 °C for 2 h to 4 h using a desiccant or hot-air hopper dryer with a dew point of -20 °C or lower. Drying temperatures above 90 °C should be avoided because pellet agglomeration may occur in the hopper. Moisture content before plastication should remain below 0.1% by mass; higher moisture levels reduce melt strength and can increase the coefficient of variation in part mass to 0.3% or more on 150 t to 300 t injection molding machines. Regrind feedstock should be kept free of copper-based heat stabilizers and halogenated flame-retardant residues; acidic decomposition products from flame-retardant grades can reduce UV stabilizer effectiveness and accelerate surface dulling. The material is not recommended for continuous submerged service in hot water above 60 °C without additional long-term hydrolysis and extraction testing.

Regulatory status follows the polypropylene copolymer framework and must be confirmed on the final compounded formulation. Typical compliance statements available from compounders include REACH registration, RoHS recast 2011/65/EU for lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE, and FDA 21 CFR 177.1520 for food-contact olefin polymers when stabilizers are permitted for the intended use. Fire performance is generally UL 94 HB at 1.5 mm; this is not a flame-retardant grade. For food-contact applications, specific migration of the UV absorber should be verified against EU 10/2011 migration limits. Automotive exterior programs may require additional OEM material specifications such as VW TL 52311 or GM GMW standards, which are not covered by generic product data.

Why Does High Stiffness Reduce Low-Temperature Impact Retention Relative to Standard Impact Copolymers?

The high-stiffness package shifts the ductile-to-brittle transition toward higher temperatures compared with a standard unfilled PP impact copolymer. In notched Charpy testing under ISO 179-1/1eA, standard impact copolymers of similar comonomer content frequently retain 6 kJ/m² to 9 kJ/m² at -20 °C, whereas the HS formulation may drop to 3.5 kJ/m² to 5 kJ/m² at the same temperature. This does not indicate a defective material; it reflects a deliberate trade-off between modulus and impact resistance. The stiffening mechanism reduces molecular mobility in the amorphous phase, raising the practical service temperature for brittle failure. Components that must survive impact below -20 °C should therefore be prototyped with the specific wall thickness, gate location, and surface texture intended for production. Thin-walled parts below 2.0 mm may retain more ductility than thick sections because cooling rate and skin orientation effects alter the elastomer phase distribution. Applications in cold-climate exterior trim should be validated by instrumented impact testing at the minimum specified service temperature rather than by 23 °C data alone.

The UV2 stabilization package does not compensate for reduced low-temperature ductility. Its function is retention of surface appearance and mechanical properties after outdoor exposure, not enhancement of subambient impact resistance. For parts requiring both high stiffness and cold impact, alternative grades with higher ethylene content, lower melt flow rate, or toughened modifier systems should be considered. The RC 14/4 HS UV2 product is most appropriate where ambient service temperatures remain above -10 °C, where sunlight resistance is a primary requirement, and where moderate flow length with reduced warpage is needed in mold design.