purified cellulose (Whatman filter paper no. 1), Riverdale sulphate pulp, Royal Kraft sulphate pulp, MoDo Crown sulphite pulp
Ingredients
cellulose, Ca(OH)2, Mg(HCO3)2, N,N-(5-nitro,1,3-phenylene)bisglutaramide, KOH, phosphate buffer
Preparation Steps
Original Recipe Text
The cellulose samples were prepared by immersion into aqueous solutions of Ca(OH)2 (0.01 mol l−1) or Mg(HCO3)2 (0.04 mol l−1) to introduce approximately 0.03 mmol g−1 of alkali. Half of the dried samples were then immersed into solutions of N,N-(5-nitro,1,3-phenylene)bisglutaramide (NPG) 0.01 mol l−1, with pH adjusted to 7 using KOH (p. 314). Artificial ageing was conducted under ISO Standard 5630/3 conditions (80°C at 65% RH) in a Vötsch VC 0020 ageing oven (p. 314). Extraction of aged samples was performed using 0.1 mol l−1 phosphate buffer (pH 7) assisted by sonification for 3 hours to perform chromatographic determinations (p. 314).
Evidence
"The cellulose samples in this work were purified cellulose (sample no. 1, Whatman filter paper no. 1, degree of polymerisation — DP = 2902) and bleached chemical cellulose samples: Riverdale sulphate pulp (sample no. 2, DP = 2535); Royal Kraft sulphate pulp (sample no. 3, DP = 2735) and MoDo Crown sulphite pulp (sample no. 4, DP = 4206)."
Remarks
The study demonstrates that hydroxyl radicals (HO•) are key intermediates in the autoxidation of alkaline paper (pH > 7). The NPG probe reacts with HO• to form coloured stable products, o-HNPG and p-HNPG, which show absorption maxima at 450–460 nm (p. 314-316). It was noted that the formation of these radicals is the driving force behind the chain-scission process (DP decrease) in bleached chemical pulps (p. 318). Higher pH in samples containing MgCO3 was linked to higher HO• production and more rapid bond scission compared to CaCO3-buffered samples (p. 318). The method is advantageous because it is non-destructive, requires small sample amounts, and is more sensitive than Electron Spin Resonance (ESR) for detecting radicals in purified cellulose (p. 313).