Braskem GR105PP 3D Printing Polypropylene Pellets are positioned within the manufacturer’s large-format additive manufacturing segment as an unfilled polypropylene homopolymer feedstock for pellet-fed extrusion systems. The designation GR105PP separates the grade from injection-moulding and blown-film polypropylene by its melt-flow index and crystallisation behaviour. The melt flow rate is 10.5 g/10 min at 230 °C under 2.16 kg load by ISO 1133-1. Density is 0.905 g/cm³ by ISO 1183-1. On single-screw pellet extruders with screw diameters from 25 mm to 45 mm and length-to-diameter ratios from 20:1 to 30:1, the material is deposited in the nozzle setpoint range of 220 °C to 240 °C. Build plate temperatures are held at 90 °C to 110 °C. The principal difference from conventional polypropylene extrusion grades is the control of melt viscosity and recrystallisation rate for layer-to-layer fusion in large bead widths and thick layer heights.

Grade-level physical property data for Braskem GR105PP are summarised below. These values are typical for the unfilled polypropylene homopolymer product category used in large-format pellet extrusion; lot-specific certificates of analysis may contain tighter limits.

What separates the melt rheology of GR105PP from conventional film extrusion grades?

Because polypropylene is a semi-crystalline polymer, the solid-to-melt transition spans a narrow interval between 130 °C and 165 °C, with the main melting endotherm near 160 °C in differential scanning calorimetry. This narrow transition produces a short thermal working window in large-format deposition. The melt flow rate of 10.5 g/10 min is lower than high-flow injection-moulding grades but higher than many sheet and thick-wall extrusion grades. This range balances bead spread against uncontrolled die swell and provides enough melt strength to bridge short gaps between deposited roads. At shear rates typical of deposition nozzles between 0.8 mm and 1.2 mm, the apparent melt viscosity for a polypropylene homopolymer of this melt flow rate lies approximately between 300 Pa·s and 500 Pa·s at 230 °C. On production-scale single-screw extruders with 20:1 to 30:1 L/D, compression ratios of 2.5:1 to 3.0:1 homogenise the melt while limiting excessive shear heating. Feed-throat temperature is maintained below 60 °C to prevent pellet softening and hopper bridging. If the feed throat approaches 70 °C, partially molten pellets can form a cohesive plug at the feed pocket and starve the screw.

Oxidative degradation is a process limit. At barrel temperatures above 250 °C and residence times longer than 10 min, random chain scission increases the melt flow rate and generates low-molecular-weight oxidation products. The upper barrel temperature should not exceed 240 °C unless the deposition head has a melt pump and residence-time control. On systems without a melt pump, prolonged idling at melt temperature has been reported to reduce bead-to-bead fusion by lowering apparent viscosity and producing a less coherent melt front.

Moisture uptake in unfilled polypropylene is low relative to polyamide, PETG, or ABS. However, surface moisture on pellets can generate steam during melting and create nozzle sputter, internal voids, and intermittent bead breakup. In production facilities with ambient relative humidity above 60 %, pre-drying at 80 °C for 4 h in a desiccant dryer is specified. Pellets stored in sealed hoppers with dry-air purge maintain residual moisture below 0.02 % by weight. Open hoppers in climates with dew points above 20 °C have been associated with first-layer adhesion loss when condensation transfers from pellet surfaces to the build plate. The material does not require the extended drying cycles common to nylon or PETG.

The starting processing window for large-format pellet extrusion is listed below. Setpoints require adjustment for nozzle diameter, extruder L/D, melt-pump presence, and build volume.

Crystallisation studies on polypropylene homopolymer of this melt-flow class show a crystallisation exotherm peak between 110 °C and 125 °C at moderate cooling rates. Slow cooling through this interval produces larger spherulites and higher shrinkage, while rapid cooling reduces crystallite size and internal stress. In large-format extrusion, the previous layer is cooled below the crystallisation peak before the next bead is deposited, which limits interpenetration of polymer chains across the interface. A heated build chamber at 80–100 °C keeps the previous layer above the crystallisation onset long enough to improve interfacial strength. The result is a trade-off between build speed, chamber cost, and part morphology. When chamber temperature is too high, parts remain soft during printing and can distort under their own weight; when too low, layer adhesion becomes the limiting mechanical property.

Deposition speed and melt throughput also affect the bead cross-section. At nozzle diameters of 1.2 mm, layer heights of 0.5 mm, and print speeds above 60 mm/s, the melt front can exhibit sharkskin or uneven bead edges unless the barrel metering zone is maintained above 220 °C. On production lines, bead width is controlled by nozzle-to-bed gap rather than extrusion multiplier alone. When the gap exceeds the layer height by more than 0.2 mm, the bead is over-squeezed and can split into separate lobes. When the gap is too large, insufficient normal force leaves a rounded bead with poor contact area to the substrate.

Bed adhesion, shrinkage compensation, and warpage control

Polypropylene has a low surface energy, typically 30–32 mN/m, which restricts wetting on untreated glass, PEI, and steel build plates. Adhesion is improved by using a polypropylene sheet, polypropylene-based tape, or a solvent-primed polyolefin interface. In production-scale prints, build plate temperatures below 90 °C cause first-layer edge curl, while plate temperatures above 110 °C soften the lower layers and increase dimensional drift in tall parts. Linear mould shrinkage by ISO 294-4 ranges from 1.0 % to 2.0 %. In additive deposition, shrinkage is anisotropic because contraction along the deposited bead differs from contraction across bead-to-bead interfaces. XY compensation factors of 1.5 % to 2.0 % and Z compensation of 1.0 % to 1.5 % are applied depending on toolpath geometry. Heated build chambers between 80 °C and 100 °C reduce differential cooling between part surfaces and interior regions. Without chamber heating, square polypropylene parts with edge lengths above 300 mm may exhibit corner lift exceeding 2 mm on open-frame systems.

Jigs, fixtures, assembly trays, and chemical-contact tooling are produced on pellet-fed systems where chemical resistance and impact toughness are more relevant than high modulus. Polypropylene homopolymer in this melt flow range resists dilute aqueous acids, bases, salts, and many polar organic solvents at ambient temperature. It is not recommended for continuous exposure to strong oxidising acids, chlorinated solvents, aromatic hydrocarbons, ketones, or hot xylene, which cause swelling or oxidative attack. At sustained service temperatures above 80 °C in air, oxidative degradation can reduce molecular weight and embrittle the part unless the grade contains a suitable stabiliser package. Published data for GR105PP-specific chemical compatibility at elevated process temperatures is limited; service testing under the actual chemical and thermal load is therefore required.

Post-processing of GR105PP parts by machining requires sharp low-rake cutting tools and moderate spindle speeds because polypropylene has a low heat deflection temperature and may smear or gum cutters. Flood coolant or compressed air is preferred over dry machining to limit local melting. Threaded inserts and heat-staked fasteners are preferred over adhesives because the low surface energy of polypropylene limits adhesive wetting. Flame or plasma treatment can increase surface polarity for bonding and painting.

When GR105PP replaces PLA, ABS, or PETG in large-format tooling

The replacement decision is governed by the trade-off among stiffness, thermal distortion, chemical resistance, and density. PLA typically has higher tensile modulus, often 3000–3500 MPa by ISO 527-2, but heat deflection temperature at 0.45 MPa is usually 50–60 °C. ABS has tensile modulus near 2000–2500 MPa and heat deflection temperature near 90–100 °C, but it releases volatile styrenics during deposition and has higher density than polypropylene. PETG has higher tensile modulus than polypropylene but density near 1.27 g/cm³ and greater moisture uptake. GR105PP reduces mass because its density is 0.905 g/cm³ and provides a low surface energy polyolefin surface with better resistance to aqueous cleaning agents. However, layer-to-layer adhesion is lower than PETG or ABS because polypropylene crystallises at the interface between deposited layers. Heated build chamber operation at 80–100 °C and nozzle setpoints at the upper end of the melt window are required to obtain useful interlayer tensile strength. Published data for Z-direction tensile strength of GR105PP in large-format printed geometries is limited; printed polypropylene commonly exhibits anisotropic tensile properties with through-thickness values below the in-plane bulk yield stress.

Compared with glass-fibre-reinforced polypropylene pellet feedstocks, GR105PP is unfilled and therefore produces lower flexural modulus. Glass-filled polypropylene grades may exceed 3000 MPa in flexural modulus, but the reinforcement increases screw and nozzle wear in pellet-fed deposition and raises melt viscosity. GR105PP lowers equipment abrasion and avoids the abrasive filler settling and nozzle clogging observed with glass-filled feedstocks in small-diameter deposition heads. Regulatory status is application-dependent. Polypropylene homopolymer of this type can be evaluated for food-contact use under FDA 21 CFR 177.1520; direct food-contact certification for GR105PP must be confirmed from the supplier. Compliance with REACH and RoHS is expected for the base polymer, but additive package and colorant compliance must be verified for the specific lot. Reclaimed printed structures and support material can be re-extruded, though repeated thermal cycles increase melt flow rate through chain scission and may shift viscosity below the lower limit of the pellet extrusion window.