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Lanxess organophosphorus flame retardants  # 4 (74), 2009

Otto Mauer
Lanxess Functional Chemicals Business Unit

Lanxess, the largest special chemicals manufacturers presents to plastics processors high quality phosphorus-containing flame retardants with unique characteristics

Flame retardants groups
Flame retardants are the largest group of polymer additives with a share of 30% exclusively of pigments and dyes. In 2007 global consumption volume for this type of additives was about 1.7 million tones. It is forecasted that the growth rate of the market will keep its positions of 3% a year generally due to consumption growth in Asia. The trend is driven not only by improving advantages of flame proof materials but also by continuously tightening fire safety standards. Flame retardants group involves thousands of commercial products containing hundreds of various chemicals. It is common practice to divide these chemicals into 6 different classes: aluminum trihydrate, bromine chemicals, organophosphorus flame retardants, antimony oxide, chlorine chemicals and others. Organophosphorus chemicals have a share of 14% of global flame retardant consumption by volume and 23% in money terms.
Organophosphorus flame retardants find their application in thermoplastic polymers and blends (PVC, PU/ABS, HIPS/POP (high impact polystyrene/ polyoxyphenylene)), thermohardering resins (PFR (phenolic-formaldehyde resins), PU, polyesters, PMMA), elastomers (NBR, SBR, CPR, EPR and others) as well as in coatings, sealers and adhesives. The main characteristics of organophosphorus flame retardants distinguishing them from other classes are their secondary properties ensuring addition processing and manufacturing benefits. That is why they are widely used as technological additives (for example for  polyol, plastisol and resin viscosity reduction), plasticizers (for PVC and acrylates), nontoxic and almost nonvolatile solvents and wetting agents (for producing high-filled, free-blowing pigment and technological additives slushes).

Adequate replacement for halogens
The most of halogen-containing flame retardants are very effective. And it is commonly believed that their substitution with organophosphorus halogen free flame retardants results in reducing of fire proof characteristics. However in many cases the statement is not right and adequate replacement of halogenated flame retardants with organophosphorus ones is particularly proven during experiments on rigid foamed PU insulation. Two insulation plates were manufactured in rigid foamed PU specially for trials. Levagard PP (tris-(2-chlorisopropyl)-phosphate) and halogen free Levagard DMPP (dimethylpropane phosphonate) flame retardants were chosen for the first and the second plate correspondingly. Both products have successfully passed SBI fireproofness test and halogen free PU insulation foam showed better characteristics by all criteria. Another example is unsaturated polyester resins. Flame retardant blends for such resins usually contain vast amount of cheap aluminum hydroxine. Disadvantages of the blends containing 300 weight parts per 100 resin parts and even greater filler amounts include high viscosity making processing more difficult and poor mechanical characteristics of hardened resin. Viscosity reduction and mechanical properties improvement can be achieved by using blends based on ammonium polyphosphate as a flame retardant. But in which case quite a high content of flame retardant (75 php) still persist. Flame retardant dosage can be reduced even greatly (down to 19 php) along with preserving material properties according to UL94 V-0 standard by means of combination of liquid phosphonate and solid phosphate. The advantages of the combination include preservation of compound low viscosity and hardened resin mechanical properties thanks to low filler concentration.
Appliance of unsaturated polyester resins for automotive parts manufacturing it is necessary to take into account smoke density generated with combustion. Halogen free organophosphorus chemicals show significantly less smoke density compared to halogenated flame retardants. During the ASTM-D 662 E smoke density tests resins with organophosphorus flame retardants show results of 220 points and resins with inorganic phosphorus flame retatdants – 150 points. For reference smoke density of unsaturated polyester resins is as much as 500 points and aluminum hydroxide – 75 points.

New composites capabilities
If there are strict requirements for flame retardant considering weight loss, virgin additives appliance will be limited because of their volatility. That is why more and more reactive chemicals which can be embedded in polymer matrix are being developed. Lanxess, special chemistry manufacturer has developed a new  reactive, halogen free organophosphorus compound posed as transparent liquid named Levagard TP  LXS
51053. Main features of the new products include high phosphorus content (about 20%) and low viscosity (about 40 mP). Hydroxyl value of the product is 300-400 mg KOH/g, acid value is less than 0.5 mg KOH/g, water content is less than 0.5%. The major advantage of Levagard TP LXS 51053 is its low volatility.
The appliance example of the new additives showing great properties considering processing, effectiveness and foam characteristic is regular flexible PU. Trials involving various flame retardants showed that Levagard TP LXS 51053 does not increase polyol viscosity, contrariwise some viscosity lowering was noticed. Blend viscosity which was about 650 mP at 230°С is not significantly higher than viscosity of cresyl diphenyl phosphate blend and lower than viscosity of bromated blends, TDCP blends, chlorinated diphosphates and control specimen. Economical advantages of the new flame retardant are as important as its technical properties. For successful FMVSS 302 test passing it was required only two pieces of Levagard TP LXS 51053 which is equal to TDCP and chlorinated diphosphate and less than DPK and bromine blend.
Thus organophosphorus flame retardants meet the most of requirements of existing and new fire safety tests; they are virtually colorless, can be easily dispersed and have valuable secondary properties such as viscosity decreasing and plasticity improving; they are very effective for various plastics including unsaturated polyesters and foamed PUs; they are halogen free (ensuring smoke corrosiveness reduction); they have moderate smoke generation and low volatility. Lanxess produces wide organophosphorus flame retardants portfolio under brand names Disflamoll и Levagard


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