Specifying PlastiComp Complēt LCF30-PA12 requires recognition that the compound is a pultruded long-carbon-fibre-reinforced polyamide 12 containing a nominal fibre loading of 30% by weight. The reinforcement is not dispersed as short monofilaments; continuous carbon fibre tows are impregnated with the PA12 matrix, drawn, and pelletized to a fixed length, typically 11–13 mm. The fibre bundles remain oriented along the pellet axis and are liberated only during plasticating. Consequently, the final moulded part retains a fibre-length distribution whose number-average length is frequently reported in the 1–3 mm range when low-shear moulding conditions are used, whereas short-carbon-fibre compounds may drop below 0.5 mm. The matrix selection of PA12 rather than PA6 or PA66 is deliberate: the longer aliphatic chain reduces equilibrium moisture uptake, improves dimensional stability in humid environments, and provides resistance to aliphatic hydrocarbons, greases, and many automotive fluids. The trade-off is a lower melting range and lower continuous-use thermal ceiling than semi-aromatic or PA66-based compounds. Application contexts include structural brackets, robotic end-effectors, housings, dry-running gears, sporting goods, and orthotic or prosthetic components.

Why Does Fibre Length Control the Onset of Fibre Fracture Versus Pull-Out?

The reinforcing efficiency of carbon fibre in a PA12 matrix is governed by the critical fibre length. For a carbon-fibre/PA12 interface with an interfacial shear strength estimated at 20–35 MPa and a fibre tensile strength near 3.5–4.0 GPa, the critical transfer length is on the order of 0.3–0.6 mm. Fibres shorter than this threshold fail to reach their tensile strength before interfacial debonding; they are extracted from the matrix, and stiffness transfer is incomplete. In a short-carbon-fibre PA12 compound, final fibre lengths after injection moulding commonly fall below 0.5 mm, so the bond surface area is small and the fibre aspect ratio may approach the critical limit. Long-carbon-fibre pellets, by contrast, produce residual fibre lengths of 1–3 mm under moderate shear, exceeding the critical length by a factor of 2–6×. This shifts the dominant failure mechanism from interfacial pull-out to fibre tensile rupture, which raises tensile and flexural strength, increases stiffness retention at elevated temperature, and improves crack-propagation resistance. Impact tests show the effect most strongly in unnotched or low-triaxiality geometries, where the continuous-fibre network can distribute energy over a larger damage zone.

Mechanical, Thermal, and Density Benchmarks Published for LCF30-PA12

Representative lot-to-lot ranges for a dry-as-moulded state, as compiled from supplier data and independent LFT-PA12 reports, are shown in Table 1. Because fibre orientation, weld-line placement, and moulded fibre length alter results, the values should be treated as directional rather than minimum specifications. Tensile and flexural properties are sensitive to gate placement; the highest numbers are obtained in flow-aligned specimens, while cross-flow and weld-line specimens can exhibit retention losses above 30–50%. Density increases relative to unfilled PA12, and the carbon fibre substantially lowers linear thermal expansion along the fibre axis. The notched Charpy and Izod values should be interpreted in the context of fibre-induced anisotropy: the crack path in a notched specimen may run along the fibre-matrix interface, so notch sensitivity is higher than in unfilled PA12 even though unnotched energy absorption is improved.

Drying of Complēt LCF30-PA12 before processing is mandatory whenever the product has been exposed to ambient air for more than 1 h at relative humidity above 60%. A desiccant dryer with a dew point at or below −40 °C should be used, with an inlet air temperature of 80–90 °C for 4–6 h or until residual moisture is below 0.10% by Karl Fischer titration. Moisture above this threshold hydrolyzes the amide bonds during melt processing, which can reduce molecular weight and produce surface splay, gas marks, and a measurable loss of tensile elongation. The recommended melt-temperature window for long-carbon-fibre PA12 is 260–285 °C; residence time should not exceed 8–10 min to avoid thermal degradation of the matrix and carbon-fibre sizing. Mold temperatures between 80 °C and 100 °C are typically required to obtain good surface replication and to avoid prematurely freezing the flow front, which would entrap exposed fibres and create a rough surface finish. Use of a general-purpose high-compression screw with a short feed section can break fibres before the melt reaches the nozzle. A low-compression screw of 20:1–24:1 L/D with a compression ratio near 2:1–2.5:1, low back pressure of 0.3–0.7 MPa, and a free-flow nozzle orifice of at least 2.5 mm is preferable. Gate thickness and land length should be at least 60–70% of the nominal wall section; pin or tunnel gates introduce high shear and reduce final fibre length. Weld lines are a particular boundary condition: because long fibres tend to orient parallel to the weld line rather than across it, weld-line tensile strength can drop below 50–60% of the base flow-aligned value. If the part cannot be gated to avoid weld lines, the strength at the weld line must be considered the design-limiting property, not the datasheet strength.

Filling behaviour differs from both unfilled PA12 and short-carbon-fibre grades. The presence of 30% long carbon fibre increases melt viscosity at low shear; minimum wall thickness below 1.5–2.0 mm can cause freeze-off before complete filling, especially at mold temperatures under 80 °C. Flow-length-to-wall-thickness ratios should be roughly 60–100:1 for short shots under typical pressures, compared with 150–250:1 for unfilled PA12. This is a rheological constraint, not a linear reduction. Hot-runner systems with small gates, sharp turns, or long residence time can damage fibres and are generally avoided; if hot runners are unavoidable, full-round or oval channels with diameters not less than 6 mm and gate diameters of 1.2–2.0 mm are used. Fibre breakage in the screw, runner, and gate consumes mechanical property margin. Moulds should be vented aggressively because carbon-filled PA12 can entrain gas from sizing decomposition and moisture; vent depth is typically 0.015–0.025 mm with land lengths of 0.5 mm.

When Moisture, Chemical Resistance, and Electrical Conductivity Shift the Part Requirements

Because the matrix is PA12, the compound has lower equilibrium moisture absorption than PA6 or PA66 grades. Saturation water uptake of unreinforced PA12 is approximately 1.5% under ISO 62 conditions; the 30% carbon fibre phase dilutes the hygroscopic polymer and reduces the macroscopic uptake to roughly 0.5–1.0% depending on laminate orientation and fibre-end wicking. This means dimensions and glass-transition-sensitive stiffness are more stable in humid air than with other aliphatic nylons; however, the compound is not a moisture barrier and should not be used as a sealing surface in continuous water contact without testing. The carbon reinforcement introduces appreciable electrical conductivity. Surface resistivity of long-carbon-fibre PA12 is typically in the semiconductive to conductive range, and the material cannot be regarded as an electrical insulator. This property may be beneficial for electrostatic dissipation or for components requiring a conductive path, but it also creates the risk of galvanic coupling when the plastic is mounted to a more noble metal in the presence of an electrolyte. Insulating bushings or isolation washers are required if the carbon-filled part is in contact with magnesium or uncoated aluminium in wet environments.

The chemical resistance profile is dominated by the PA12 matrix, which is resistant to aliphatic hydrocarbons, diesel fuel, greases, hydraulic fluids, and zinc chloride solutions. Strong acids, strong oxidizing agents, phenols, and some chlorinated solvents are known to attack polyamide 12 and should be avoided. In fuel-contact applications, PA12 is used in tubing and connectors, but the long-fibre grade should not be assumed to meet permeability or extraction requirements without test data to SAE J2260 or equivalent. Immersion can also reduce fibre-matrix adhesion because water and polar solvents migrate along the interface; tensile strength in 50% relative humidity is therefore similar to dry values, but after prolonged hot-water ageing the fibre-matrix debonding can reduce transverse tensile properties by 20–40% relative to dry-as-moulded.

Compared with unfilled PA12, Complēt LCF30-PA12 shifts the modulus from roughly 1.4–1.6 GPa to 18–22 GPa, an increase of more than an order of magnitude, while tensile elongation at break falls from typical ductile values above 50–200% to about 1.5–2.5%. The material therefore replaces ductile snap-fit geometries poorly but is appropriate for stiffness-dominated brackets, frames, and load-bearing housings that would otherwise require metal. Against a short-carbon-fibre PA12 compound, the long-fibre architecture typically preserves higher notched and unnotched impact energy at equal fibre weight fraction, reduces the drop in fatigue resistance under cyclic loading, and improves creep resistance. The difference is most visible at low temperatures, where short-fibre compounds lose matrix ductility and long-fibre networks still resist crack extension. Against long-glass-fibre PA12, the carbon-fibre grade has higher tensile and flexural modulus at similar fibre volume fraction, lower density, and lower linear thermal expansion; however, it is also electrically conductive, more costly, and more abrasive to screws, barrels, and moulds. The grade should not be specified as a direct drop-in replacement for a long-glass-fibre part without reviewing tooling wear, gate sizing, and electrical isolation. In rotating or sliding parts, carbon fibre provides self-lubricating and wear-reducing behaviour relative to glass-filled PA12, but the wear surface will generate conductive dust that may interfere with adjacent electronics. These contrasts define the selection boundary: Complēt LCF30-PA12 is most useful where specific stiffness, fatigue resistance, dimensional stability, and chemical exposure coexist, and least suitable where weld-line strength, electrical insulation, low abrasive tool wear, or high ductility govern the design.