Analysis And Reaction Of THP Salts With Hide Collagen

Tetrakis hydroxymethyl phosphonium salts which will be referred to herein as "THP salts"have long been used as fire-retardants for textile and bactericide. Later THP salts were also used in oil field water treatment system and cooling water system because of their foamless, low toxic and biodegradable performances. In 1950's THP salts were tried in leather production and nowadays they became the research focus of chrome-free tanning materials again. The condensations of THP salts and resorcinol and the conjunction of THP salts with melamine formaldehyde are effective main tanning agents giving leather high hydrothermal stability. Out of question, the reactive hydroxymethyl of THP salts can combine with amido groups of collagen but there was few report about the reaction of THP salts with other groups of collagen. The study of the reaction of THP salts with collagen was important for the development of THP chrome-free tanning agents. The determination of tetrakis hydroxymethyl phosphonium chloride, hereafter abbreviated as THPC, was first studied. Iodimetry and potassium iodate can be used to determine the content of THPC in THPC samples. The THPC content in hide powder and substitute of collagen can be determined by spectrophotometric method. First, the hide powder should be digested thoroughly in order to convert THPC to orthophosphate, and then the digested solution will be distilled for a few hours. After these were comlpeted the content of P in the solution can be determined by phosphor-molybdenum blue method then the content of THPC will be obtained. Polycaprolactam, poly vinyl alcohol and butylamine were used as the substitutes of amido, hydroxy and amino group of collagen protein that reacted with THPC. It was found that THPC mainly combined with amino groups of collagen and the cross-linking degree was 2.2. THPC also linked with hydroxyl groups and amido groups of collagen. The combination capacity between THP salts and hydroxyl groups and amido groups changed with pH and at pH 6.0 it reached the maximum. It was also found that THPOH or TrHP or the mixture of them was the effective crosslinking agents and TrHPO was not reactive with hide collagen. It was found that the crosslinking between THP salts and amino compounds in situ can improve the hydrothermal stability of the hide. When THP salts penetrated into leather first and then dicyandiamine were enriched the shrinking temperature of the leather reached 90 ℃. The tanning was most effective when performed by first impregnating the leather with a THP salt, in the succession of dicyandiamine and then raising the pH above 6. The optimal mol ratio is n(THPS):n(dicyandiamine)=0.41:1,n(THPC):n(dicyandiamine)=1.76:1. It was also found that THPS has a better crosslinking property than THPC. The leather tanned by THP salts was full and soft and the grain was satin. The shrinking temperature was 90℃, the tensile strength was 18.8Mpa and the tearing strength was139.9N/mm. The heat aging property and storage property of THP salts tanned leather was superior relatively to glutaraldehyde and oxazolidine tanned leather.