Derivatives of native lignin from annual fibre feedstocks
The present invention provides derivatives of native lignin having certain aliphatic hydroxyl content. Surprisingly, it has been found that consistent and predictable antioxidant activity may be provided by selecting for derivatives of native lignin having certain aliphatic hydroxyl content.
1. A method of producing an annual fibre lignin derivative having an aliphatic hydroxyl content of from about 1 mmol/g to 3.25 mmol/g, a normalized RSI of 15 or greater, and a weight average molecular weight of from about 500 g/mol to about 5000 g/mol, comprising:
a) pulping an annual fibre biomass by a pulping process selected from the group consisting of: steam explosion, acid hydrolysis, ammonia fiber expansion, autohydrolysis, sulphite pulping and modifications thereof, kraft process and modifications thereof, soda pulping and modifications thereof, and organosolv process;
b) heating the pulp;
c) maintaining the elevated temperature for 1 minute or longer;
d) separating the cellulosic pulp from the lignin rich pulp; and
e) recovering derivatives of native lignin, wherein the derivatives have an aliphatic hydroxyl content of from about 1 mmol/g to about 3.25 mmol/g, a weight average molecular weight of from about 500 g/mol to about 5000 g/mol, and a normalized RSI of 15 or greater.
2. The method according to claim 1 , wherein the pulping process is steam explosion.
3. The method according to claim 1 , wherein the pulping process is an organosolv process.
4. The method according to claim 1 , wherein the pulping process is sulphite pulping.
5. The method according to claim 1 , wherein the pulping process is acid hydrolysis.
6. The method according to claim 1 , wherein the pulping process is kraft process and modifications thereof.