Flame-retardant coatings for rigid polyurethane foam based on mixtures of polysaccharides and polyborate
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Flame-retardant coatings for rigid polyurethane foam based on mixtures of polysaccharides and polyborate Isao Tsuyumoto
Ó American Coatings Association 2020 Abstract New types of flame-retardant coatings for rigid polyurethane foam (RPUF) are developed using mixtures of amorphous sodium polyborate (SPB) and various polysaccharides. Based on our previous research reporting that the RPUF coated with a mixture of SPB and starch shows high flame retardancy, polysaccharides such as carboxymethyl cellulose, hydroxyethyl cellulose, glucomannan, 2-hydroxypropyl guar gum (HPG), and gellan gum are used instead of starch. By coating each mixture on the surface, the RPUF (10 mm thickness) endures the premixed flame of butane gas burner with length of 100 mm for more than 12 min, and the backside temperatures remain within the range of 100–160°C. The high flame retardancy is successfully achieved with lower adhesive amounts of the mixtures (8.9–19.1 mg/cm2) than that of the starch/SPB mixture (51.3 mg/cm2). Water resistance is also substantially improved by using gellan gum, CMC, or glucomannan with NaOH. The elution ratio when immersed in water for 12 h is significantly suppressed to 4.8% using the gellan gum/SPB mixture compared with 80.1% using the starch/SPB mixture. The differential thermal analysis and thermogravimetry of the coating mixtures and the scanning electron microscope observations of combustion residues suggest the flame-retardant mechanism that a carbonaceous foam layer is produced from polysaccharides by the action of SPB foam layer and both of the foam layers protect inside from heat and oxygen. Keywords Flame retardant, Polyurethane, Foam, Borate, Polysaccharide, Coating
I. Tsuyumoto (&) Department of Applied Chemistry, College of Bioscience and Chemistry, Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichi, Ishikawa 9218501, Japan e-mail: [email protected]
Introduction Polyurethane foam (PUF) is widely used for various applications such as heat insulators in buildings and refrigerators, cushions in cars, trains and upholstered furniture, and mattresses. Flame-retardant treatments of PUF are essential for fire prevention because it easily catches fire and goes up in flames due to high contact area with air. As for PUF, halogenated phosphate esters such as tris (1-chloro-2-propyl) phosphate (TCPP), tris (1,3-dichloro-2-propyl) phosphate (TDCP), and tris (2-chloroethyl) phosphate (TCEP) have been extensively used as the flame retardants, though their restrictions are recommended by the European Commission (EU) because of a potential carcinogenicity risk for infants.1–3 Concerns regarding human health are increasing because toxic compounds may be released in fire, disposal, and normal use of the halogenated flame retardants, and thus many researchers have been intensively investigating nonhalogenated flame retardants.4–6 Red phosphorus has been reported to impart high flame retardancy specifically to polyurethane foam, while red phosphorus itself is a highly combustible hazardous materia
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