The influence of temperature and moisture on the optical properties of cellulose in the presence of metal chlorides and glucuronic acid

• The influence of Mg2+, Ca2+, Fe3+ ions and glucuronic acid on the dry and humid heat-induced (120180C) discoloration of cotton linter sheets was investigated. The quantity of the added metal ions was similar to that of metal ions found in wood and pulp. Heat-induced ageing (120150C, pH 5) under dry conditions caused only slight discoloration of the reference sheets and of the sheets impregnated with the metal ions. However, during ageing at 180C, the presence of Mg2+ ions accelerated the discoloration. An initial pH in the range of 38 had no great influence on the discoloration of the reference sheets, but a low pH in combination with Mg2+ ions increased the discoloration drastically. Under humid ageing conditions at 180C (<30 min), the sheets discolored approximately twice as much as under dry conditions; the difference in discoloration caused by the metal ions was less than in dry ageing. Adding glucuronic acid to the sheets caused extensive discoloration under dry ageing conditions (120180°C), while Ca2+ and Mg2+ ions decreased the glucuronic acid induced discoloration. Under humid conditions (180°C), however, Mg2+ and Ca2+ ions did not prevent the discoloration caused by glucuronic acid. An increase in the absorption coefficient was observed at 285 nm, most likely due to the formation of 5-hydroxy-2-methyl-furaldehyde (HMF) and 2-furaldehyde (furfural). GC-MS analysis reveals increased formation of HMF in the sheets impregnated with Mg2+ ions. Degradation of the cellulose in which the alkaline earth metals act as Lewis acids is proposed.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Pappers-, massa- och fiberteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Paper, Pulp and Fiber Technology (hsv//eng)

Nyckelord

Cellulose

Discoloration

Temperature

Calcium

Magnesium

Iron

HMF

Furfural

Cellulose and paper engineering

Cellulosa- och pappersteknik

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)