Browsing by Author "Maree, Chelaine"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Lignin phenol formaldehyde resins synthesised using South African spent pulping liquor
    (Stellenbosch : Stellenbosch University, 2021-12) Maree, Chelaine; Gorgens, Johann F.; Tyhoda, Luvuyo; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: The current study investigated to which extent phenol could be replaced by lignins to produce lignin phenol formaldehyde (LPF) resins. This was done utilising soda lignin and sodium lignosulphonate as by- products from the South African pulping industry. These industrial lignins were characterised for phenolic hydroxyl group content, proximate analyses, mid- infrared (IR) spectroscopy, and thermogravimetric analyses (TGA). Soda black liquor was either spray- dried or acid precipitated to isolate the soda lignin. The acid precipitated soda lignin was then further acid purified. The lignosulphonate was received in spray-dried form and purified using a dialysis membrane of 3500 Da. Purified soda lignin indicated the highest reactivity towards formaldehyde and was therefore investigated further to produce LPF resins at 60%, 80% and 100% substitution of phenol by lignin. The LPF resins were characterised for their free formaldehyde content, pH values, mid-IR spectroscopy, thermogravimetric analyses, and shear strength. At 60% and 80% substitution a one-pot phenolation and LPF synthesis method was used where the soda lignin was first phenolated before formaldehyde was added, while at 100% substitution no phenolation was performed. Phenolation increased the phenolic hydroxyl content by up to 105% and 124% at 80% and 60% substitution, respectively. Three face-centred central composite designs (CCD) were used to attain the maximum adhesive strength at each substitution level. The parameters optimised in each CCD included the phenolation reaction temperature, sodium hydroxide to phenolated lignin (NaOH/PL) ratio, and formaldehyde to phenolated lignin (F/PL) ratio. The best synthesis reaction conditions at 60% and 80% substitution were at the lower bound of the range tested, with a NaOH/PL molar ratio of 0.124 and a F/PL molar ratio of 1. At 100% substitution without any modification, the optimum NaOH/PL molar ratio was 0.477, while the best F/PL molar ratio was at 3, which was the upper bound of the tested range. Plywood made with LPF60, LPF80, and LPF100 resins attained their highest shear strengths of 0.786, 1.09, and 0.987 MPa, respectively, which adhered to the GB/T 14732-2013 standard (≥ 0.7 MPa). A substitution level of 68% produced the highest shear strength of 1.11 MPa. The good performance of this soda lignin as a LPF resin was further confirmed by producing high-density particleboard with the LPF68 resin giving a MOR and MOE of 40 MPa and 3209 MPa, respectively, which adhered to the ANSI A208.1-1999 standard. Furthermore, good resistance of the resin to water absorption (37.2 wt%) and thickness swelling (13.5 wt%) was also proven. This unclean pulping lignin was the first lignin to produce LPF resins at 100% substitution, without requiring modification or additives.