Carbohydrate composition in Eucalyptus wood and pulps: Comparison between Py-GC/MS and acid hydrolysis

In analytical pyrolysis, carbohydrates are degraded into stable anhydrosugars, which are analyzed by GC/MS. The benefit of Py-GC/MS is that fiber composition including carbohydrates, lignin and its S/G ratio can be determined simultaneously from fiber-based materials without need of extensive pretreatment, contrary to the traditional method. In this study, the relative carbohydrate composition of various Eucalyptus species was determined by Py-GC/MS. In addition, pulps produced from the same species by soda-AQ and soda-O₂ processes were analyzed similarly. The results were compared with those obtained by acid hydrolysis followed by HPLC. This comparison showed that the relative carbohydrate composition determined by Py-GC/MS for the wood samples differed from the values obtained by acid hydrolysis. Significantly better correlation between the two methods was observed for the pulp samples cooked to varying kappa number levels. Fractionated pyrolysis was applied in order to find explanation to the observed difference in the degradation behavior of carbohydrates in wood and pulp samples. Due to the close association of lignin and carbohydrates, the thermal behavior of lignin was followed as well. The results showed that the thermal behavior of xylan and cellulose differed in the wood samples, but were almost equal in the pulp samples. Thermal degradation of xylan was similar with lignin in both sample types. Similar thermal behavior between the components is a prerequisite for reliable Py-GC/MS analysis. Therefore, this method cannot be recommended for the comparison of carbohydrate compositions between different wood raw materials. However, it is applicable to pulp samples and may find application in research for profiling carbohydrate compositional changes with processingmethods: and conditions.