Polycarbonate Rod, Medical Grade

Medical-grade polycarbonate rod is gamma-stabilised stock produced from resin the manufacturer states meets USP Class VI and ISO 10993 for NON-IMPLANTABLE medical applications, lot controlled and traceable. That qualifier is the most load-bearing phrase in the sentence and it is the manufacturer's own. It is suitable for gamma, electron-beam and ethylene-oxide sterilisation, and for limited autoclaving. Mechanical properties are those of unfilled polycarbonate: specific gravity 1.20, tensile at yield around 9,000 to 10,000 psi, flexural modulus around 340,000 psi, heat deflection 270F at 264 psi.

Four things to be straight about, because this is the area where listings overclaim most. "Medical grade" is not a standard and implies nothing by itself. The compliance attaches to the resin, not to the sheet, the rod or the part you machine from it - biocompatibility of a finished device has to be established by the device manufacturer. Gamma stabilisation is about resisting yellowing during sterilisation, not about biocompatibility, and the two get conflated constantly. And autoclaving is published as limited, not unlimited: polycarbonate is hydrolysis-sensitive and repeated steam cycles degrade it, so this is not an autoclavable material in the sense a customer usually means.

It is machined into instrument handles and housings, fluid-path and laboratory components, device fixtures, and single-use or limited-reuse parts.

Machining and annealing. Polycarbonate machines cleanly with sharp tools and good chip clearance, and it is notch-sensitive, so avoid sharp internal corners, scribed lines and deep tool marks - that sensitivity is the same effect that makes published notched impact figures scatter so widely. Machine-grade plate and rod are supplied stress-relieved and most machined parts need no annealing. Consider annealing when you remove a large proportion of the stock, when you remove it mostly from one face, or when the part will see chemical exposure, because residual machining stress plus a marginal chemical is the main cause of stress crazing. The cycle we work to for unfilled polycarbonate is a ramp to 275F over about four hours, a hold of 30 minutes per 1/4 inch of thickness and a cool-down at 50F per hour, fixtured to prevent distortion, with critical dimensions finish-machined afterwards. Glass-filled grades anneal at 290F.

Chemical compatibility and cleaning, which is where most polycarbonate failures start. Clean it with mild diluted dish soap and a soft microfibre cloth, or an ammonia-free glass cleaner. Do NOT use ammoniated glass cleaner - the common blue kind - because ammonia attacks polycarbonate, and the resin maker's own testing shows 0.1% ammonia is enough to do damage in the presence of water. Also avoid abrasive or high-alkaline cleaners, scrapers and squeegees, dry rubbing, and solvent in direct sun. Isopropyl alcohol diluted 50/50 with water handles oil and tar. Acetone, MEK, methylene chloride, chloroform, toluene, xylene and aromatic fuels all attack it, and so do amines and the plasticisers that migrate out of flexible PVC - which is why PVC gasket, tape and cable tie contact is a real failure mode. The important subtlety is that chemical resistance is not a fixed property: stress cracking only develops where the part is in tension, so a cold-bent, over-torqued or tightly framed part will fail with chemicals a compatibility chart calls safe.