Specification-grade polycarbonate (PC) is an amorphous aromatic engineering thermoplastic produced from bisphenol A and a carbonyl source. Density measured by ISO 1183-1 is typically 1.19–1.21 g/cm³. Transparent unfilled grades exhibit light transmission of 88–90% at 3.0 mm thickness when tested to ASTM D1003. The material is supplied as cylindrical pellets or compounded granules, and downstream processing is sensitive to moisture, molecular weight distribution, and accumulated heat history. A purchase specification for PC therefore depends on verifiable supplier status: an authorised distributor, a stockist, or a trader. Data on a certificate of analysis (CoA) is meaningful only when the chain of custody is documented and the test methods are named.

Authorised, Stockist or Trader? Reading a Polycarbonate Supplier's Real Position

An authorised distributor holds a direct contractual relationship with the resin manufacturer. The distributor receives material under the manufacturer’s quality management system and supplies it with an unchanged certificate of analysis. Lot traceability runs from the manufacturer’s production batch to the distributor’s warehouse management system. ISO 9001:2015 clause 8.4 requires control of externally provided processes, products and services; an authorised distributor can demonstrate this control with a documented chain of custody, supplier audit records, and release specifications.

A stockist maintains physical inventory but may source from multiple authorised distributors and secondary channels. The stockist may provide an original CoA for stored lots, but the CoA alone does not prove that material was stored at the correct temperature and humidity. Polycarbonate pellets are hygroscopic; storage in non-dried conditions can increase surface moisture to levels above 0.02% by mass. A stockist without a manufacturer agreement may not have access to change notifications, formulation disclosure, or technical product stewardship.

A trader operates as a spot-market reseller and may not hold continuous physical inventory. Documentation may be a copy of a CoA from an earlier cargo, and material may be sourced from surplus, cancelled orders, or repacking operations. Without physical lot verification, regrind, wide-spec material, or heat-aged inventory can enter the supply chain. In a regulated production environment, this creates a quality risk that cannot be resolved by incoming visual inspection alone.

Polycarbonate pellets equilibrate with ambient humidity because the polymer repeat unit contains carbonate linkages susceptible to hydrolysis at processing temperatures. Moisture content above 0.02% by mass, measured by Karl Fischer titration according to ASTM D6869, is sufficient to produce splay, silver streaking, and a measurable reduction in molecular weight during melt processing. On a production-scale injection moulding line with barrel temperatures from 280°C to 320°C and a 25 mm screw with L/D 20:1, wet PC can exhibit viscosity loss and impact strength decrease. A desiccant dryer with a dew point of −40°C to −30°C is required for 3–4 h at 120°C for standard grades. Higher-capacity systems using a hopper throat at 80°C and closed-loop desiccant beds maintain pellet surface moisture below 0.02%. An authorised distributor can supply the original lot code and drying recommendations; a trader generally cannot confirm storage conditions.

When a Distributor’s CoA Omits Melt Volume Rate Data

Melt volume rate (MVR) at 300°C and 1.2 kg load, tested to ISO 1133-1:2022, is the routine proxy for molecular weight in polycarbonate. A certificate of analysis that omits MVR or reports only melt flow rate without the corresponding test temperature and load prevents a moulder from detecting off-spec resin. The MVR of standard injection moulding grades typically lies between 6 cm³/10 min and 22 cm³/10 min; extrusion grades may be 3–6 cm³/10 min; high-flow optical media grades may exceed 25 cm³/10 min. A shift of 2–3 cm³/10 min from the original lot can indicate regrind content, heat exposure, or an off-spec polymerisation batch. In an authorised distribution channel, the CoA carries the same MVR value as the manufacturer’s release specification and identifies the analytical method. In a trader channel, the documentation may report a nominal value that cannot be traced to a specific silo lot.

Acceptance testing for specification-grade PC normally covers the group of properties listed below. The values are typical reference points from published datasheets; exact limits are grade-specific and should be taken from the manufacturer’s technical datasheet.

The presence of these values on a CoA, with a lot number and production date, indicates a specification-grade supply. Absence or conflicting values should be treated as a supply-chain risk rather than a minor documentation gap.

Thermal Stability, Regrind Content and Melt Viscosity Drift

Repeated heat histories degrade polycarbonate by hydrolysis and oxidative chain scission. At moulding temperatures above 320°C, prolonged residence times above 5 minutes can produce yellowing, gas bubbles, and molecular weight reduction. On a 36 L/D co-rotating twin-screw compounding line with vacuum venting at −0.08 MPa, melt viscosity drift is controlled by stabiliser level, screw speed, and residence time; an unknown heat history from a trader-supplied lot introduces a variance that cannot be predicted from a copied CoA. Regrind content above 20% by mass can lower notched impact strength by 10–25% compared with virgin material, depending on the number of heat cycles and drying conditions. An authorised distributor provides virgin resin with a defined regrind policy or a certified post-consumer recycled grade. A stockist or trader may not be able to declare the regrind fraction because incoming material may have been repalletised or blended.

For food-contact polycarbonate, the resin must comply with FDA 21 CFR 177.1580 and, in the European Union, Commission Regulation (EU) No 10/2011 with specific migration limits. For medical devices, the resin supplier may support the manufacturer’s assessment under ISO 10993-1, but the supplier typically provides a formulation disclosure or change-management agreement. An authorised distributor maintains these documents under version control and issues change notifications when the manufacturer modifies the polymerisation stabiliser package or mould-release system. A stockist without manufacturer authorisation cannot guarantee that a specific lot reflects the same formulation as the qualification lot. Traders may not be able to provide an EU declaration of conformity for REACH Article 33 or a RoHS Directive 2011/65/EU Annex II compliance statement for cadmium, lead, mercury, hexavalent chromium, PBB and PBDE.

A Supply-Chain Audit Framework for PC Resin Documentation

Purchasing polycarbonate for a controlled manufacturing process requires a documentation audit that includes the certificate of analysis, certificate of conformance, safety data sheet, REACH SVHC statement, RoHS Annex II statement, and the supplier’s ISO 9001:2015 certificate scope. The CoA should list the raw material lot number, production date, test methods, results, and signatory. The CoC should confirm that the lot conforms to the manufacturer’s sales specification. A physical audit should include warehouse temperature and humidity records, pest-control logs, and segregation of approved and non-approved lots. If the supplier cannot produce these documents for a specific lot before shipment, the purchase is not a specification-grade supply chain.

Polycarbonate is compounded with UV stabilisers, flame retardants, and glass fibre for outdoor, electrical, and structural applications. In a 20 wt% short glass fibre PC compound, flexural modulus can rise from approximately 2.3 GPa to 5.5–6.5 GPa, while tensile stress at break may shift into the 90–110 MPa range; MVR at 300°C/1.2 kg commonly falls below 5 cm³/10 min. These changes are measured by ISO 527-2 and ISO 178. A supplier with an authorised line to the manufacturer can provide a matched lot of UV-stabilised PC with a defined UV package and documented accelerated weathering data under ISO 4892-2. Flame-retardant PC compounds tested to UL 94 and IEC 60695-11-10 can achieve V-0 at 1.5 mm thickness, but the rating depends on the specific formulation and additive package; off-spec material may still be presented with a copied UL yellow card in an unauthorised channel. A stockist or trader may offer material labelled as “UV grade” without the additive concentration or weathering certificate, leaving the moulder unable to predict yellowness index shift after 1000 h of xenon arc exposure.