Buying recycled polycarbonate: PCR content claims and how to verify them requires treating a supplier declaration as a chain-of-custody data set rather than as a material-grade property. Polycarbonate (PC) is a bisphenol-A–based engineering thermoplastic with a glass transition temperature near 147 °C when measured by differential scanning calorimetry per ISO 11357-2:2020; this transition remains useful as a first-pass identity marker in recycled streams. Virgin PC density is close to 1.20 g/cm³ per ISO 1183-1:2019, which provides only a weak contamination check because filled or blended recycled compounds shift density in different directions. Post-consumer recycled (PCR) feedstocks for PC derive from 19 L water carboys, glazing sheet, lighting covers, medical housings, and optical-media scrap. Each source carries a different additive package, coating residue, flame-retardant history, and weathering signature. A claim of “post-consumer recycled polycarbonate” without a numeric mass fraction, a documented chain-of-custody model, and a third-party certificate is insufficient under ISO 14021:2016, Section 7.8, which requires self-declared recycled content claims to state pre-consumer and post-consumer fractions separately and to be supported by traceable inventory records. The central verification problem for PC is that the recycled repeat unit is chemically identical to virgin resin; no routine analytical instrument can directly read the PCR percentage from a molded part. Verification therefore operates in two linked domains: document audit and degradation or contamination testing.

What Is Actually Measurable in a Recycled PC Lot?

ATR-FTIR confirms the polycarbonate backbone through the carbonyl absorption near 1775 cm⁻¹ and C–O stretching near 1220 cm⁻¹, but it cannot quantify recycled content. Melt flow rate measured per ISO 1133-1:2022 at 300 °C/1.2 kg is more informative: a post-consumer lot with suppressed molecular weight due to hydrolysis, UV exposure, or multiple heat histories will present as a higher melt flow rate than the corresponding virgin grade. Virgin low-viscosity injection-grade PC commonly falls between 10 g/10 min and 30 g/10 min under those conditions; a PCR lot that arrives 25% above the supplier’s certificate of analysis value is a candidate for reduced melt strength, excessive drool, and thinner weld lines. Differential scanning calorimetry per ISO 11357-2:2020 can expose contamination from PET or ABS because PET displays a melting endotherm near 250 °C and ABS a second glass transition near 100–110 °C. However, a compounded PC/ABS blend will also show the ABS transition; therefore, contamination screening must be paired with FTIR and ash analysis rather than thermal analysis alone. Ash content per ISO 3451-1:2019 is a useful low-cost indicator of inorganic contamination. Values above 0.10 wt% for translucent PC suggest metal flakes, label foil, or filler carryover from mixed post-consumer bales. Yellowness index measured per ISO 17223:2014 or ASTM E313-20 tracks thermo-oxidative and UV history; recycled PC from greenhouse or automotive glazing can show elevated yellowness before melt flow rate reveals degradation, making optical properties a sensitive early-warning test for applications requiring transparency.

Chain-of-Custody Documentation Under ISO 22095

ISO 22095:2020 defines identity preserved, segregated, controlled blending, and mass balance chain-of-custody models. For recycled PC, true identity preserved or segregated supply is rare outside closed-loop water-bottle collection systems because mixed bales from municipal material recovery facilities are the dominant feedstock. Mass balance is the commercial default: certified PCR input tonnage entering a production site is allocated to output lots over an accounting period, not by physical tracing of each pellet. A buyer verifying a PCR claim should request the mass-balance ledger, PCR input weight tickets, conversion-loss records, and the certificate number under UL 2809 or an equivalent third-party scheme. The certificate should state the PCR percentage, feedstock category, chain-of-custody model, and certification scope; a certificate that lists only “recycled content” without the model cannot be audited against ISO 22095:2020. ISCC PLUS operates as a mass-balance sustainability certification, not as a polymer test method, and therefore provides no analytical evidence for the presence of post-consumer PC in a molded component. REACH obligations remain separate: electronic-origin PC scrap should be screened against the Candidate List of substances of very high concern and legacy brominated flame retardants, especially when the source is display housings or monitor equipment.

Incoming lot verification should follow a three-part sequence: document audit, identity confirmation, and degradation marker measurement. The certificate of analysis should list moisture content per ISO 15512:2019, melt flow rate per ISO 1133-1:2022, ash per ISO 3451-1:2019, and, for transparent grades, yellowness index per ISO 17223:2014. A missing moisture value is a more immediate process risk than a missing PCR declaration. PC hydrolyzes when moisture remains above 0.02 wt% at melt temperatures, generating carbon dioxide and phenolic end groups; the visible result is silver streaking and a measurable upward drift in melt flow rate. Pre-drying in a closed-loop desiccant dryer with a dew point no higher than −40 °C and an air temperature of 120 °C for 4 h is standard for flake or pelletized PCR PC, followed by moisture verification before melt processing.

The acceptance windows in the table are for incoming lot quality, not for certified PCR content. Because no routine analytical test can measure PCR percentage directly, the document package remains the primary proof of recycled content; the physical tests are used to detect whether the recycled lot can survive the intended process without excessive viscosity loss or contamination. If a dispute arises, size-exclusion chromatography can be used for molecular weight root-cause analysis, but it does not identify the post-consumer origin of the polymer. Covert tracer masterbatches can be used in closed-loop, high-value PC streams, but they are not a generic verification method for merchant PCR compounds.

When Melt Flow and Moisture Interact in Production

At melt temperatures above 300 °C, residual moisture in PC becomes a kinetic driver for carbonate hydrolysis. The interaction is nonlinear: a lot that measures 0.03 wt% moisture may produce surface defects in a high-shear injection screw even if its melt flow rate is within specification. Injection molding of PCR PC on a 1200 kN clamp machine with a two-cavity test mold typically requires a melt temperature of 280–320 °C, a mold temperature of 70–120 °C, and a screw-back pressure below 1.5 MPa to limit shear heating. If melt flow rate shifts more than 25% relative to the certificate of analysis, the process window narrows: short shots appear in flow-length-limited cavities, weld-line strength drops, and clamp force requirements change because the lower viscosity pack pressure requirement is altered. In extrusion compounding with a corotating twin-screw extruder of 40:1 L/D, vacuum venting at −0.08 MPa or better is required to strip volatiles from post-consumer fractions; without venting, moisture and degradation gases remain in the melt and create splay, voids, and additional hydrolytic chain scission.

A production-scale evaluation for PCR PC should include a purge of the injection molding machine with virgin PC to establish a baseline fill ratio, then a switch to the PCR lot under identical injection velocity and melt temperature. The fill ratio difference across 20 consecutive shots should not exceed 5% if the PCR material is to be used interchangeably with virgin PC in an existing tool. Tensile properties per ISO 527-2:2012 from a Type A specimen provide an objective mechanical check: virgin low-viscosity PC typically retains elongation at break above 50%, while a contaminated or extensively degraded PCR lot can fall below 25%, even when the yield stress appears unchanged. Notched impact testing per ISO 180:2019 is a more sensitive probe for immiscible contamination, because small polyolefin or PET domains act as stress concentrators and reduce impact resistance before tensile yield changes. For critical load-bearing applications, the purchaser should require positive identification of the recycled feedstock stream, not simply a percentage claim; published data for specific PCR PC configurations is limited, so a limited-scale molding trial under the intended part’s wall thickness and gate geometry is the most direct verification of fitness for use.

An alternate production-scale approach for PC PCR is compounding at the converter site. A corotating twin-screw extruder with 40:1 L/D, side-feed dosing, and vacuum venting at −0.08 MPa can blend PCR PC with virgin PC at controlled ratios, but the PCR claim on downstream parts must reflect the actual PCR mass fraction after the blend. Metering losses at hopper feeders and screw retention of material create batch-to-batch variance; therefore, the actual PCR fraction may lag the target by 2% to 5% unless the feeder calibration is verified with traceable weights. This variance is process-specific and must be measured on the line, not assumed from the pellet certificate.