Depolymerization of ethylene diamine-pretreated pulp samples

It is necessary to establish a common protocol for the complete dissolution of pulp, plant holocellulose, and cellulose in a solvent suitable for measuring their molar masses and molar mass distributions. Soaking pretreatment of wood chemical pulp, holocellulose, and bacterial, tunicate, or algal cellulose samples in ethylene diamine (EDA) for 4 days facilitates the complete dissolution of such samples in 8% LiCl/N,N-dimethylacetamide. The molar mass parameters of the samples may then be obtained by size-exclusion chromatography with multiangle laser light scattering and refractive index detection. However, when hardwood bleached kraft pulp (HBKP) samples were pretreated with EDA under an air atmosphere for 4 days, their degrees of polymerization (DPs) were clearly lower than those pretreated with EDA for 1 day. In contrast, bacterial cellulose or mercerized cotton lint cellulose had almost the same DP values between the EDA-pretreated sample for 1 and 4 days. When the HBKP was reduced with NaBH₄ before EDA pretreatment under an air atmosphere for 4 days, or soaked in EDA under an N₂ atmosphere for 4 days, the DP value became similar to that of the sample pretreated in EDA under an air atmosphere for 1 day. Thus, one of the above pretreatments is required for reliable and reproducible DP values for HBKPs. The obtained results indicate that the carbonyl groups present in the HBKP hemicellulose fractions participate in the depolymerization behavior by EDA pretreatment under an air atmosphere for 4 days.

Graphical abstract