Nano4elec BIO EC 12 Conductive Carbon Black Polylactic Acid Injection Grade

Conductive carbon black polylactic acid compounds are specified for injection-moulded antistatic and electrostatic dissipative parts where bio-based polymer content and controlled surface resistivity must coexist. Nano4elec BIO EC 12 is a polylactic acid carrier compounded with conductive carbon black and supplied as cylindrical pellets. The grade nomenclature indicates an injection-moulding rheology rather than a masterbatch or extrusion-only formulation. Lot-specific values for filler content, melt index, and electrical performance should be taken from the supplier certificate of analysis because conductive carbon black dispersion and percolation behaviour are batch-sensitive.

The following sections define the product in terms of material identity, processing constraints, electrical response, and the differences observed when BIO EC 12 is substituted for other conductive thermoplastics or alternative conductive fillers. Published data for the exact formulation of this proprietary grade is limited; therefore, representative ranges for conductive carbon black PLA compounds are given where the supplier datasheet must be consulted for final acceptance limits.

Material Identity and Specification Scope

BIO EC 12 is based on a polylactic acid carrier. The biobased carbon fraction of the unfilled PLA portion can be confirmed by ASTM D6866-22 Method B; the petroleum-derived conductive carbon black lowers the total biobased carbon content relative to unfilled PLA. The compound is generally processed after drying to a residual moisture content below 0.025% (250 ppm) to limit hydrolytic chain scission in the barrel. Because PLA is hygroscopic, exposure to ambient air above 60% relative humidity for more than 30 min can increase surface moisture and produce splay, viscosity loss, or intermittent conductivity at the part surface.

These ranges describe the performance envelope commonly observed for conductive carbon black PLA injection grades. They should not be used as acceptance limits for BIO EC 12 without the supplier’s lot-specific data, especially where electrical performance is safety-related or where the moulded part must pass an ESD audit under ANSI/ESD S20.20.

Processors should also request the melt viscosity curve at three shear rates, typically 100 s⁻¹, 500 s⁻¹, and 1000 s⁻¹, because a single melt flow index does not adequately describe mould-filling behaviour for a shear-thinning carbon black compound. Poor dispersion of the conductive carbon black can produce isolated high-resistance regions on welded knit lines and at gate blush zones.

Drying is performed in a desiccant dryer with a dew point not higher than -40 °C. A common drying condition for PLA-based conductive compounds is 80 °C for 4 h. Higher temperatures may soften the pellets and cause bridging in the hopper, while lower temperatures may not remove moisture below the 250 ppm threshold within a practical cycle time.

Injection moulding barrels with a general-purpose screw of 20:1 to 24:1 L/D and a compression ratio of 2.0:1 to 2.5:1 are acceptable. A shut-off nozzle is preferred because carbon black compounds can drool at high back pressure. The back pressure is typically maintained between 0.3 MPa and 0.8 MPa to preserve dispersion without excessive shear heating. Screw speed is usually held below 150 min⁻¹ for medium-diameter barrels to limit frictional temperature rise and PLA molecular weight loss.

What Moulding Defects Appear When Moisture or Residence Time Exceeds the PLA Window?

The primary processing boundary for BIO EC 12 is thermal degradation of the PLA carrier. Melt temperatures above 220 °C for extended residence can produce a viscosity reduction, brown discoloration, acrid odour, and loss of impact strength even when the part fills correctly. Total melt residence time should be kept below 8 min at a melt temperature above 210 °C. If a machine interruption stops production, the barrel should be purged with unfilled PLA or the rear zones reduced to 150 °C until production resumes. The occurrence of black specks in unfilled purge material after a stop is an indicator of carbon black agglomeration and degraded PLA char, not a normal pellet defect.

Moisture-related splay is often observed as silver streaking oriented from the gate. The defect is misinterpreted as trapped air from the vent. A dew-point check and a residual moisture test on the dried pellets should be completed before altering vent depth. If the dryer dew point is above -30 °C, drying capacity is insufficient for humid plant conditions.

Knit lines in conductive PLA show a local increase in surface resistivity. In a test plaque with a single edge gate, the weld line formed around a core pin may measure one to three decades higher in surface resistivity than the bulk surface when measured with a two-point probe. Reducing melt temperature to improve weld line strength is not recommended because it also reduces knit-line conductivity. Instead, the gate position should be moved to place the knit line away from the ESD-sensitive contact region, or the wall thickness should be increased to 2.5 mm or above at the weld zone to improve melt fusion.

Excessive shear heating in a small-diameter screw can raise the actual melt temperature above the set barrel temperature. A melt purge at 210 °C set point may exit at 230 °C if the back pressure is high and the screw speed is above 200 min⁻¹. Therefore, melt temperature should be confirmed with a probe rather than assumed from barrel settings. The mould cooling water should be kept at 10–20 °C to solidify the part rapidly and reduce cycle time, but mould temperatures below 10 °C can increase surface stress and reduce surface conductivity through skin-layer orientation.

For thin-wall parts below 1.5 mm, the flow resistance of conductive carbon black PLA can require higher injection pressure, which increases molecular orientation and increases surface resistivity in the frozen skin. Published data for this specific configuration is limited, but industrial trials with similar compounds indicate that wall thicknesses from 2.0 mm to 3.0 mm provide a wider processing window and more uniform surface conductivity.

Tool steel wear is generally moderate with carbon black at ESD loadings, but the abrasive character of the filler can increase screw and barrel wear compared with unfilled PLA. Nitrided or bimetallic barrels and wear-resistant screw tips are used for extended campaigns. A production run above 50,000 cycles on an untreated screw can exhibit screw diameter loss sufficient to change melt temperature stability and reduce melt homogeneity.

Static dissipation behaviour depends on carbon black network formation. The percolation threshold is the filler loading at which a continuous conductive network forms. Below the threshold, surface resistivity remains high; above it, resistivity drops by several orders of magnitude over a narrow concentration range. For many carbon black/PLA systems, surface resistivity falls from above 10¹² Ω/sq to below 10⁶ Ω/sq within a few weight percent of carbon black. Overloading beyond the percolation threshold increases melt viscosity, reduces elongation at break, and produces little additional conductivity benefit. The conductive network may be partially destroyed by high shear or by long melt residence time, which is why regrind addition should be limited to 20% unless in-house moulding trials confirm stable surface resistivity. Higher regrind levels can generate dark streaks and uneven conductivity because the carbon black network in previously moulded material is not identical to the original dispersion.

When Conductive Carbon Black Replaces Metal Fibres in Bio-Based ESD Packaging

BIO EC 12 differs from metal-fibre-filled conductive thermoplastics in several practical ways. Metal fibres provide low resistivity, often below 10² Ω/sq, but they increase density, create anisotropic conductivity due to fibre orientation, and can corrode in the presence of moisture or cleaning agents. Carbon black compounds provide isotropic conductivity, lower density, and no galvanic corrosion, but they do not reach the same low resistivity as metal fibres. For ESD packaging and electronics handling trays, surface resistivity in the range of 10³–10⁶ Ω/sq is sufficient under IEC 61340-5-1 and ANSI/ESD S20.20, and carbon black is therefore used as a lower-cost and simpler alternative to metal fibre compounds.

Compared with carbon nanotube PLA grades, BIO EC 12 is expected to require higher filler loading to reach the same conductivity, with a greater loss of impact strength and a higher melt viscosity at equivalent filler volume. Carbon nanotube grades may achieve ESD-range surface resistivity at loadings below 5 wt%, while carbon black grades may require 10–15 wt% depending on carbon black structure and surface area. The trade-off is cost and dry-handling complexity: carbon black is less expensive but dustier, and dispersion quality is more difficult to maintain across large silo-to-press transfer systems.

When BIO EC 12 is compared with conductive carbon black ABS or polycarbonate compounds, the PLA carrier offers a bio-based polymer backbone but lower heat resistance and lower impact strength. ABS-based ESD compounds can be used where parts are exposed to temperatures above 80 °C or where drop-impact resistance is specified. PLA-based compounds are better suited to single-use or short-life ESD logistics items, trays, covers, and interior components that are not exposed to high heat or solvents. The chemical resistance of PLA is limited; strong alkalis, certain esters, and hot water can degrade the surface, increase surface resistivity, and cause embrittlement.

The following table summarises the comparative position of carbon black PLA injection grades in ESD applications.

BIO EC 12 is differentiated within the conductive carbon black PLA category by its injection-grade melt flow rather than a masterbatch dilution or a high-viscosity extrusion grade. In practice, injection-grade compounds must balance carbon black loading against melt flow. A compound with identical surface resistivity but lower melt flow may require higher melt temperatures or higher injection pressures, which in turn degrade the PLA carrier and narrow the processing window. The injection-grade designation therefore refers not to a single viscosity value but to a viscosity envelope that permits filling of multi-cavity tools without exceeding the thermal degradation limit of PLA.

For parts requiring flame retardancy, the use of PLA-based conductive compounds is more restrictive than for ABS or polycarbonate. Many halogen-free flame retardants increase melt viscosity and further reduce impact strength. If a UL 94 V-0 rating is required, the processor should confirm whether BIO EC 12 can be modified without loss of ESD performance. Published data for the flame-retarded configuration is limited.

Dimensional stability is another consideration. PLA has a relatively low heat deflection temperature, and post-mould shrinkage can continue with time and temperature. For precision ESD trays, the part geometry should be measured after 24 h at 23 °C and 50% RH. The coefficient of linear thermal expansion for carbon black PLA is typically between 60 × 10⁻⁶ K⁻¹ and 80 × 10⁻⁶ K⁻¹, which is lower than unfilled PLA due to the rigid filler, but still higher than many glass-filled amorphous thermoplastics. Tolerances below ±0.05 mm across a dimension above 100 mm may require increased mould cooling time or a stabilised post-mould conditioning step.

As REACH and RoHS Both Apply to ESD Enclosures in Electronics Logistics

Compliance statements for BIO EC 12 should be obtained from the supplier for each production lot. Conductive carbon black itself is not classified as a hazardous substance under REACH Regulation (EC) No 1907/2006 in its cured polymer-bound state, but the supplier must confirm whether the carbon black grade contains polycyclic aromatic hydrocarbons within the limits given in REACH Annex XVII Entry 50. For plastics used in electronics packaging, the compound should comply with Directive 2011/65/EU (RoHS) for lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ethers. The standard test methods for RoHS screening are not limited to X-ray fluorescence; wet chemical confirmation by IEC 62321-5:2013 or IEC 62321-7-2:2017 is used when XRF results are near the threshold.

For food-contact or cosmetic-contact applications, the processor must not infer compliance from the bio-based nature of PLA. Carbon black used in food-contact polymers in the European Union is regulated under Commission Regulation (EU) No 10/2011 with specific purity requirements for the carbon black. A separate declaration of compliance is required from the compound supplier. In the United States, carbon black may be used under applicable 21 CFR sections if the grade meets the specification for the intended use. The presence of conductive carbon black at ESD loadings is not automatically covered by general PLA food-contact approvals, and the processor should verify the final article under the relevant migration test conditions.

Measurement of surface resistivity on moulded parts should be standardised. IEC 62631-3-2 specifies the test method for surface resistivity of solid insulating materials, while ASTM D257-14 is commonly referenced in North America. The measured value is sensitive to electrode pressure, probe geometry, conditioning time, and relative humidity. Parts tested immediately after moulding can show higher surface resistivity than parts conditioned for 48 h at 23 °C and 50% RH. For acceptance testing, a two-point probe is not equivalent to a concentric ring electrode. The concentric ring geometry with a defined potential difference of 100 V is preferred for ESD audit documentation under IEC 61340-5-1.

Because surface resistivity is influenced by mould release agents, the use of silicone-based external mould release is not recommended. Silicone films can insulate the surface and raise measured resistivity by several orders of magnitude even when the bulk compound is conductive. If mould release is unavoidable, a compatible non-silicone grade should be validated on moulded plaques, with surface resistivity measured before and after application. The same applies to post-mould coatings, labels, and adhesives that cover the ESD contact surface.

For waste and recycling, PLA-based conductive compounds are not compatible with conventional mixed-polymer recycling streams. The carbon black filler hinders near-infrared sorting and can contaminate clear PLA regrind. Industrial composting of carbon black PLA requires conditions meeting EN 13432 or equivalent, but the conductive carbon black fraction is not biodegradable. Processors should separate regrind from standard PLA waste and confirm the disposal route with the compound supplier. If in-house closed-loop regrind is used, the maximum regrind level should be established by measuring surface resistivity and melt flow on a five-batch trial, not by analogy with unfilled PLA.