Polyurethane Additives (Incuding Polyurea And Polyisocyanurate Additives)
Since Polyurethane (PU) chemistry was discovered in Germany in 1937, this versatile plastic material has enjoyed uninterrupted growth globally and today comprises about 5% of all plastic sold in the world. The applications for Polyurethane are, in order of consumption - furniture and bedding (flexible foam), Automotive (Flexible foams, moulded foams, elastomers and coatings), construction (rigid foam panels), coatings and adhesives, appliances (rigid foam insulation) and many industrial parts (mainly elastomers).
Beyond the two major raw materials used to produce a PU system, namely Polyol and Isocyanate, there are a great number of chemical products which are added to control or modify the processing of Polyurethanes and their final properties.
These additives include, chain extenders, crosslinkers, catalysts, stabilisers, anti-oxidants, processing aids, colorants, flame-retardants, adhesion promoters, solvents, diluents, plasticisers and moisture scavengers. Southern Chemicals is active in servicing the Southern African region for these additives. Specifically materials available in stock include:
Chain-extenders, curing agents and crosslinkers are generally low-molecular weight polyols or polyamines used to improve PU properties. Typically chain-extenders and curing agents are used in flexible PU’s, microcellular elastomers, casting elastomers, polyureas, adhesives and coatings. Hydroxyl (OH) groups react with diisocyanates to form polyurethane hard segments while amine groups react with diisocyanates to form polyurea hard segments. Those hard segments segregate, resulting in modulus increase and higher glass transition (Tg).
Southern Chemicals supports local customers with the following glycol and diamine chain extenders and crosslinkers.
- Diethylene Glycol (DEG)
- Dipropylene Glycol (DPG)
- 1,4 Butane Diol (BDO)
- 2-Methyl-1,3 Propane Diol (MP-Diol)
- Diethanolamine (DEOA)
- Ethylene Diamine (EDA)
- Isophorone Diamine (IPDA)
- Diethyltoluene diamine (DETDA)
- Dimethylthiotoluene diamine (DMTDA)
- Tetramethylhexanediamine (TMHDA)
- Hexamethylenediamine (HMDA)
- Polyetheramine D230, D400, D2000
In the absence of catalysts, the isocyanate group (NCO- ) reacts rather slowly with hydroxyl groups (-OH) and water itself. The catalyst choice for PU manufacture is therefore directed at obtaining an optimum profile among several reactions that can occur during the process. Different catalyst types are used for the reaction of an isocyanate with water or polyol. Catalysts here are typically an aliphatic or aromatic tertiary amine, or an organometallic compound. Tertiary amines are mostly used to catalyze the polyaddition reaction of isocyanate with water, forming urea and CO2. On the other hand organometallic catalysts are mainly used to catalyze the polymerization reaction of an isocyanate and a polyol. Carboxylic acid salts of alkaline metals, phenols and symmetrical triazines are used to catalyze the isocyanate to form a polyisocyanurate (PIR).
Catalysts are selected to promote either the “Gel” reaction (polyaddition), or “blow” reaction (Water/isocyanate forming CO2). Also, “balanced” blends of these catalysts are available. Further, delayed catalysts have become important in flexible moulded foams, where it is important to combine good flowability (into the mold) with short demold times.
The following list represents the main catalyst types currently available ex-stock from Southern Chemicals:
- Dimethylethanolamine (DMEA)
- Dimethylethoxyethanolamine (DMEE)
- Bis(2-dimethylaminoethyl)ether (BDMAEE) (A-1)
- Triethylene diamine (TEDA solid and bends)
- Pentamethyldiethylenetriamine (PMDETA)
- Dimethylpiperazine (DMP)
- Dimethylcyclohexylamine (DMCHA)
- Dimethylbenzylamine (BDMA)
- Pentamethyl-dipropylenetriamine (PMDETA)
- Triethylamine (TEA)
- Dimethylaminopropylamine (DMAPA)
- N-Ethyl morpholine (NEM)
- Stannous Octoate
- Dibutyltin Dilaurate
- Potassium Acetate
- Potassium Octoate
- Dimethyltin mercaptide
Most PU foams are made with the aid of non-ionic, silicone-based surfactants. They perform several functions in the system which are critical to the foam properties.
- Reduce surface tension
- Emulsify incompatible formulation components
- Promote nucleation of air during mixing
- Stabilize the rising foam
- Control cell-size in the final foam.
Antioxidants (Anti-scorch agents)
These materials are included to inhibit the tendency of polyurethane foams to undergo oxidation when exposed to oxygen at normal or elevated temperatures. The effect of “scorching “ in flexible foams is in effect oxidation due to high processing temperatures which can occur in high-water formulations or when foams are processed in high humidity climates. The addition of antioxidants available from Southern Chemicals will help prevent scorching and physical deterioration of foams due to this phenomena.
All polyurethanes based on aromatic isocyanates will turn dark shades of yellow upon aging and exposure to light. The yellowing can be a concern due to aesthetic considerations and will often be visible depending on the foam covering. Typical generic chemistry applied in antioxidants include Benzotraizoles and Benzophenones which are available from Southern Chemicals.
Southern Chemicals maintains stock of high-quality polyether-based colourants for PU foams and plastics. Available are black, red, blue, yellow, and violet. These products display low viscosities with excellent dispersions for homogenous colour deelopment.
Plasticizers can be either reactive or non-reactive. Non-reactive plasticizers are generally esters which are used mostly in PU elastomers. Phthallate plasticisers which were commonly used are being replaced by improved non-toxic types such as the “Benzoflex” range supplied by Southern Chemicals.
PU Processing Additives
Southern Chemicals supplies a number of processing aids for the PU foam industry. Their incorporation into, “on the edge” formulations will allow the manufacturer to achieve unique foam properties. For example, using the “Geolite” range of additives will enable the formulator to process very low TDI-index formulations, resulting in softer feel foam. Also by reducing the TDI-index, higher water levels can be added, reducing the methylene chloride addition levels. Other additives avaible will allow for higher load-bearing foams to be produced within a given density range. Flame Retardants
Flexible PU foams have a large surface area and high air permeability and thus will burn on ignition. Flame retardants are often added for safety and legislative reasons. In flexible foams, the most widely used flame-retardants are chlorinated phosphate esters. Chlorinated paraffin and melamine are also used but to a lesser extent .
Available currently from Southern Chemicals:
|Used in flexible and rigid PU foams|
|Used in rigid PU foams|