Thioplast®G (unmodified polysulfide) types are ideal for their most important application as a sealant because the key properties of cured Thioplast® G are elasticity and pronounced chemical resistance. As regards curing conditions, their behaviour is uncritical. Physical properties are also easy to adapt to specific application requirements using various fillers, plasticisers and special modifying additives.
Chemistry of THIOPLAST® G
Thioplast results from the polycondensation of bis-(2-chloroethyl-)formal with alkali polysulfide. This reaction generates long-chain macromolecules which are then cut to the required chain length by reductive splitting with sodium dithionite. The disulfide groups are at the same time converted into reactive thiol terminal groups. By introducing a trifunctional component (e.g. 1, 2, 3-trichloropropane) during synthesis, a third thiol terminal group can be added to a specific number of Thioplast molecules to determine the extent of cross-linking during the curing process. The value for n may vary between 7 and 38 depending on the amount of the splitting agent used. For particular applications, chain length and branching will have to be varied. The chemical composition of liquid G-type THIOPLAST® is described in outline in the following structural formula:
Typical properties
All Thioplast types are medium to high viscous liquids of light brown color. The average molecular weight (calculated from the thiol terminal group content), as a measure of chain length and the degree of branching, determine the viscosity. Consequently, viscosity is the most important characteristic feature of a THIOPLASTT® G type.
Characteristic features of the Thioplast types
(see pdf file)
Application field Sealants
THIOPLAST® of the G type are typically used as basic polymer for sealants, but may also be used for other applications. Typical applications are:
- manufacturing of insulating glass
- construction
- machine, marine and aircraft industry
- coatings (e.g. concrete coatings)
- molding compounds
- modification of epoxies and rubbers
- leather impregnation
- grinding wheel binder
- printing blankets
THIOPLAST® G Types
Akzo Nobel currently manufactures nine types of THIOPLAST® G, differing in molecular weight (chain length) and degree of branching. This product range will meet requirements for most applications, but specific, tailor-made polymers can be produced on special request.
Compounding
Thioplasts are base polymers for elastic, chemical and weather resistant sealants. Using various fillers, plasticisers and special modifying additives it is possible to adjust the physical properties of Thioplast polymers to meet specific application requirements and to reduce material cost.
The choice of the Thioplast type depends on the desired processing and application properties of the compound. Higher branched types provide high-elastic hard products after curing whereas lower branched types lead to weak-elastic products that have excellent resistance to chemicals and weathering.
Low viscosity types enable the formulation of pouring highly reactive compounds. High viscosity Thioplast types are mainly used for gun grade compounds.
Product Data Sheets
Thioplast® G (G1, G4, G10, G12, G21, G22, G44, G112, G131)
Processing
Thioplast compounds are commonly formulated as one or two component systems. The A part contains the Thioplast polymer, the B part the curing agent. A one component system consists of a complete package containing all ingredients. They are mixed under low humidity conditions prior to packaging in air tight, moisture resistant containers and will cure when exposed to environmental moisture.
Preparing the compounds requires the use of planetary mixers or high speed dispersers. A triple-roll mill should be additionally used to produce a maximum of uniformity of the curing paste and reduction of occluded air.