Methylene Chloride Polycarbonate Solvent

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Designated MC-PC-99.9/AN, the product is an amylene-stabilised methylene chloride solvent system intended for controlled dissolution of bisphenol A polycarbonate homopolymer and copolymer feedstocks in coating, casting, recovery, and solvent-cement applications. The model suffix AN indicates the amylene stabilizer package; PC identifies the polycarbonate-processing grade; 99.9 refers to the minimum assay of 99.9% methylene chloride by capillary gas chromatography with flame ionisation detection. The solvent corresponds to CAS 75-09-2, EINECS 200-838-9, and the chlorinated solvent specification ASTM D4701. It is supplied in 200 L epoxy-lined steel drums or 1,000 L stainless steel intermediate bulk containers under nitrogen blanket. The amylene content of 20–50 ppm suppresses acid-catalysed decomposition during storage in unlined steel and high-density polyethylene packaging; water content is controlled below 50 ppm by ASTM E203 because moisture promotes hydrochloric acid formation in the presence of polycarbonate hydrolysis products. Typical nonvolatile residue is below 10 ppm by ASTM D2109, and acidity as HCl is below 5 ppm by ASTM D2106. This grade is differentiated from general-purpose methylene chloride by its tighter nonvolatile residue limit and its stabilizer specification, which allow use in optical polycarbonate film casting where surface defects from residual impurities and acid attack are critical.

What limits solution viscosity and filtration throughput in polycarbonate dissolution?

For unwrapped bisphenol A polycarbonate pellets of 1 mm nominal diameter, dissolution in MC-PC-99.9/AN at 25 °C and 101.325 kPa proceeds to a transparent solution in a closed baffled stainless steel dissolver when the stirrer tip speed is held above 2.5 m/s. Pellet moisture must be reduced to below 0.02% by drying at 120 °C for 4 h before dissolution; moisture above this threshold accelerates hydrolysis, lowers solution viscosity, and creates carbon dioxide bubbles during subsequent film drying. For a 20 wt% solution of 30,000 g/mol weight-average molecular weight polycarbonate, Brookfield RV DV2T readings with an SC4-27 spindle at 25 °C typically lie between 900 mPa·s and 1,800 mPa·s. The dominant source of variation is not average molecular weight alone, but the presence of gel-like skins and dust from high-shear compounding; these fragments raise filtered pressure at a 3 µm absolute-rated polypropylene depth filter above 1.0 bar in less than 20 min unless a 10 µm sintered stainless steel guard filter is installed. Dissolution is exothermic and the solvent’s normal boiling point of 39.6 °C is reached locally if polycarbonate is added too rapidly; a jacketed vessel with chilled water at 10 °C on the reactor jacket is employed when the addition rate exceeds 2 kg/min per 100 L of solvent. Open-top mixing is not used because the vessel headspace concentration exceeds the OSHA 25 ppm 8-hour time-weighted average unless local exhaust ventilation maintains capture velocity above 0.5 m/s.

Post-industrial polycarbonate regrind from optical disc and automotive glazing lines is recovered by dissolving the ground flake at 12–18 wt% in MC-PC-99.9/AN inside a nitrogen-blanketed 500 L glass-lined dissolver maintained at 35 °C. The glass-lining specification avoids metal-ion extraction from steel vessels, which otherwise appears as iron contamination in the precipitated polymer and as brown discoloration after prolonged contact with slightly acidic solvent. The solution is passed through 10 µm and 2 µm polypropylene depth filters in series, then injected into methanol antisolvent under high-shear mixing between 1,500 rpm and 2,500 rpm. The resulting polycarbonate powder shows a median particle size of 150–350 µm and is washed with deionised water until conductivity falls below 10 µS/cm. The recovered resin is dissolved again in MC-PC-99.9/AN and tested according to ISO 1628-4 to confirm that the viscosity number remains within 5% of the feedstock value. Greater deviation indicates chain scission from alkaline antisolvent carryover or from metal contamination. Contact surfaces in this operation are limited to 316L stainless steel, borosilicate glass, or high-density polyethylene; aluminium, zinc, and carbon steel are excluded because residual acidity and trace water can generate corrosion products that increase ash residue and reduce polycarbonate clarity after re-precipitation.

Amylene-stabilised solvent recovery and impurity rejection limits

Solvent recovery from polycarbonate solutions is performed in a wiped-film evaporator with a jacket temperature not exceeding 80 °C and a condenser outlet near 5 °C. The feed must be filtered to remove polymer gels larger than 5 µm before entering the evaporator; unfiltered feed causes mechanical fouling on the wiper blades and lowers heat-transfer coefficient by more than 20% over a 72 h production run. The amylene stabilizer in the 20–50 ppm range suppresses hydrochloric acid accumulation in the recovered distillate; unstabilised methylene chloride recovered from polycarbonate solution containing 50 ppm water develops acidity above 5 ppm as HCl within 72 h under humid storage. ASTM D2106 titration of the recovered solvent is used as the batch-release control, and batches exceeding 5 ppm acidity are redistilled over a sodium bicarbonate bed or rejected for optical-grade film casting. Across a 0.5 m² wiped-film evaporator operating at 40–60 kg/h feed rate, methylene chloride recovery typically exceeds 95% by mass. However, when the polycarbonate feedstock contains oligomers below 1,000 g/mol, the distillate nonvolatile residue can exceed 10 ppm by ASTM D2109, requiring a fractional distillation column operated at 2:1 to 4:1 reflux ratio to reject oligomers. Compared with high-boiling chlorinated solvents such as 1,1,2,2-tetrachloroethane, recovery energy is lower because the methylene chloride distillate can be condensed at 5 °C against standard chilled water rather than vacuum or high-pressure steam. This is the primary energy difference when solvent recovery is integrated into continuous polycarbonate dissolution lines.

When methylene chloride replaces tetrachloroethane in polycarbonate film casting

Film casting trials replacing 1,1,2,2-tetrachloroethane with MC-PC-99.9/AN require a reformulated drying profile because methylene chloride has a normal boiling point of 39.6 °C compared with 146.5 °C for tetrachloroethane, and a vapour pressure at 20 °C of approximately 47 kPa. In a closed-loop film caster with a 3 m heated zone and a slot-die gap of 300 µm, the first drying zone is held at 25 °C for 30 s to avoid surface skinning and blister formation. The second and third zones are set at 45 °C and 60 °C respectively, remaining below the polycarbonate glass transition to prevent premature film orientation. Residual solvent in the cast film is controlled below 50 ppm by static headspace gas chromatography according to ASTM D4526. The lower solvent viscosity of methylene chloride at 25 °C, approximately 0.42 mPa·s versus 1.75 mPa·s for tetrachloroethane, yields lower solution viscosity at equivalent 18 wt% polycarbonate solids and improves levelling, but edge bead formation increases because the faster evaporation rate concentrates polymer at the slot-die exit. Unlike tetrachloroethane, methylene chloride does not require high-pressure steam for recovery; however, closed-loop ventilation and condenser recovery are mandatory to meet the OSHA 25 ppm 8-hour exposure limit. The lower viscosity also permits higher solids loading while maintaining a shear viscosity below 2,000 mPa·s for slot-die coating, whereas tetrachloroethane solutions of the same polymer reach that limit at lower solids. Published data for direct pilot-scale substitution is limited, so drying profiles are verified by residual solvent measurement rather than by residence time alone.

For polycarbonate solvent cementing and adhesive compounding, MC-PC-99.9/AN is used as carrier solvent at 5–10 wt% polycarbonate resin solids. The cement is applied by syringe or brush inside a ventilated enclosure with capture velocity above 0.5 m/s, and the assembled joint is held at 23 °C and 50% relative humidity for 24 h. Tensile-shear testing according to ASTM D3163 on 3.0 mm polycarbonate sheet results in cohesive substrate failure when residual methylene chloride in the bond line is below 100 ppm, measured by headspace gas chromatography. Drying faster than 24 h or below 40% relative humidity produces surface whitening at the joint edge because rapid cooling from solvent evaporation condenses ambient moisture; this is controlled by adding 2–5 wt% of a high-boiling retarder such as cyclohexanone only when the downstream application can tolerate the slower release. The solvent cement is incompatible with amine-catalysed epoxy compounds, which can induce polycarbonate stress cracking at the joint interface.

Batch-release limits establish the minimum acceptable purity for optical film casting

For optical film casting, the 10 ppm nonvolatile residue limit is the controlling specification; residues from general-purpose chlorinated solvents leave visible surface defects in film thinner than 100 µm. The 0.5 ppm iron limit prevents metal-catalysed darkening of polycarbonate during long solvent recovery cycles. Water above 50 ppm increases the acidity of recovered solvent and raises the risk of carbonate hydrolysis when the solution is stored at 35 °C for more than 72 h. The amylene stabilizer is intentionally kept below 50 ppm to avoid plasticising the final film or altering the glass transition temperature; residual amylene is stripped with the methylene chloride in the drying zones.

MC-PC-99.9/AN is classified as a chlorinated solvent; occupational exposure is controlled under OSHA 29 CFR 1910.1052 with an 8-hour time-weighted average of 25 ppm and a short-term exposure limit of 125 ppm. In the European Economic Area, methylene chloride is restricted in paint stripper formulations under REACH Annex XVII Entry 59; this restriction does not apply to industrial polycarbonate processing but requires demonstration of worker exposure control. The solvent is not supplied for consumer paint removal or for open-vapour degreasing. Contact with aluminium powder, zinc, or magnesium must be avoided because finely divided metals can decompose chlorinated solvents under exothermic conditions. The product should not be blended with strong oxidizers or with amine-based additives in the same tank, because amine reactions can generate hydrochloric acid and accelerate polycarbonate chain scission. For all applications, the solvent transfer system is equipped with conductive piping and nitrogen blanketing to exclude moisture and reduce vapour release. Published data for long-term polycarbonate solution stability in this specific formulation is limited to internal batch records, so each production lot is re-tested for viscosity number retention after 72 h at 35 °C before release for optical film casting.