Treating catalytically oxidized nanofibrillar cellulose hydrogel

A heat treating method for preventing a greater than 30% change in viscosity of nanofibrillar cellulose hydrogel, the method comprising:

• providing an oxidized nanofibrillar cellulose hydrogel having a dry-matter content of at least 0.6 weight-%, wherein the oxidation has been carried out through N-oxyl mediated catalytic oxidation of cellulose-based raw material, and has at most 50 μmol of aldehyde groups per gram of dry nanofibrillar cellulose;
• subjecting the nanofibrillar cellulose hydrogel to a heat treatment, wherein the heat treatment comprises heating the nanofibrillar cellulose hydrogel at a predetermined temperature within the range of 100-150° C. in a closed environment, for a period of time in the range of 1 second to 180 minutes, wherein the predetermined temperature and the period of time are chosen such that the number of viable micro-organisms in the nanofibrillar cellulose hydrogel is reduced;
• and
• cooling the nanofibrillar cellulose hydrogel to a temperature below 80° C. in the closed environment,
• wherein the nanofibrillar cellulose hydrogel after the heat treatment has a viscosity of 2000-40000 mPas as measured at a 0.8% (w/w) concentration of the nanofibrillar cellulose in water with a Brookfield viscometer at a temperature of 20° C., with a vane spindle and a measuring speed of 10 rpm.

A heat treated nanofibrillar cellulose hydrogel formed using a heat treating method for preventing a greater than 30% change in viscosity of nanofibrillar cellulose hydrogel, the method comprising:

• providing an oxidized nanofibrillar cellulose hydrogel having a dry-matter content of at least 0.6 weight-%, wherein the oxidation has been carried out through N-oxyl mediated catalytic oxidation of cellulose-based raw material, and has at most 50 μmol of aldehyde groups per gram of dry nanofibrillar cellulose;
• subjecting the nanofibrillar cellulose hydrogel to a heat treatment, wherein the heat treatment comprises heating the nanofibrillar cellulose hydrogel at a predetermined temperature within the range of 100-150° C. in a closed environment, for a period of time in the range of 1 second to 180 minutes, wherein the predetermined temperature and the period of time are chosen such that the number of viable micro-organisms in the nanofibrillar cellulose hydrogel is reduced;
• and
• cooling the nanofibrillar cellulose hydrogel to a temperature below 80° C. in the closed environment,
• wherein the heat treated nanofibrillar cellulose hydrogel has a viscosity of 2000-40000 mPas as measured at a 0.8% (w/w) concentration of the nanofibrillar cellulose in water with a Brookfield viscometer at a temperature of 20° C., with a vane spindle and a measuring speed of 10 rpm.