Methylzinnmercaptid — Frequently Asked Questions

Mixed-metal stabilisers form metal soaps and chlorides that scatter light, but methyltin mercaptides dissolve in the PVC and leave no opaque residue. They also replace unstable chlorine atoms in the polymer early in processing, which prevents the yellowing that shows first in clear products. That combination of clarity and early colour is why they remain the benchmark stabiliser for clear rigid film, sheet and bottles.

Monomethyltin compounds react quickly and mainly protect early colour, while dimethyltin compounds work for longer and provide long-term heat stability. Grades with more monomethyltin give brighter initial colour; grades with more dimethyltin give a longer processing window before degradation. The best ratio depends on your process time and temperature, so compare grades by ratio as well as tin content.

Dosage is expressed in parts per hundred resin (phr). Rigid pipe formulations typically use about 0.3–0.6 phr, because pipe tolerates some colour and has a short heat history. Clear sheet and film usually need about 1.0–2.0 phr for colour and clarity. Lubricants, fillers, processing temperature and regrind content all change the requirement, so confirm the dosage in your own trials.

EU REACH Annex XVII entry 20, mirrored in UK REACH, restricts tri-substituted organotins and certain dibutyltin and dioctyltin compounds in some articles. Methyltin compounds are not named in that entry. An importer should still confirm that each component is registered for the import, check the safety data sheet classification, and ask for impurity data on other organotins if the finished article falls within a restricted use.

CPVC processes at higher temperatures than PVC and needs a stabiliser with more long-term heat stability. A separate methyltin grade formulated for CPVC is listed for that purpose. Standard grades may be used in some CPVC blends, but check with a processing trial, because an under-stabilised CPVC compound can degrade rapidly in the extruder.

The sulfur-containing ligands carry a characteristic odour, which becomes stronger if moisture or heat hydrolyses the ester groups in storage. Keep drums tightly closed in a cool, dry place and use stock in rotation. During processing, local exhaust ventilation at the extruder or calender removes vapour. Low-odour grades exist; if odour matters in your finished product, mention it in the enquiry.