Two constitutional structural schemes are proposed attempting to unify and rationalize a series of focused NMR and chromatographic determinations aimed at providing an integrated picture for the structure of softwood kraft lignin.

The need for renewable alternatives to conventional petroleum based polymers has been the motivation for work on biobased composites, blends and materials whose foundations are carbon neutral feedstocks. Lignin, an abundant plant derived feedstock and waste byproduct of the cellulosic ethanol and pulp and paper industry, qualifies as a renewable material. Despite the fact that it is often difficult to blend lignin with other polymers due to its complex structure and reactivity, published research over the past decades, has focused on issues such as lignin miscibility with other polymers, the thermal and mechanical strength behavior of its copolymers and its fractions as well as efforts at tuning its thermal properties via chemical modifications and other means. As such, this study attempts to offer a comprehensive overview that largely discusses the importance of these processes with the aim of finding an effective, cost efficient and environmentally friendly means that may allow the utilization of this important and largely ignored biopolymer.

The main difficulties in wood and pulp analyses arise principally from their numerous components with different chemical structures. Therefore, the basic problem in a specific analytical procedure may be the selective separation of the main carbohydrate-derived components from lignin due to their chemical association and structural coexistence. The processing of the wood determines some structural modification in its components depending on the type of wood and the applied procedure. Fourier transform infrared (FT-IR) spectrometry and X-ray diffraction have been applied to analyze Eucalyptus g. wood chips and unbleached and chloritebleached pulp. The differences between samples have been established by examination of the spectra of the fractions obtained by successive extraction (acetone extractives, acetone free extractive samples, hemicelluloses, and lignins) by evaluating the derivative spectra, band deconvolution, etc. The energy and the hydrogen bonding distance have been evaluated. The relationship between spectral characteristics and sample composition has been established, as well as the variation of the degree of crystallinity after pulping and bleaching. The integral absorption and lignin/carbohydrate ratios calculated from FT-IR spectra of the IR bands assigned to different bending or stretching in lignin groups are stronger in the spectrum of eucalyptus chips than those from brown stock (BS) pulp spectra because of the smaller total amount of lignin in the latter. FT-IR spectra clearly show that after chlorite bleaching the structure of the wood components is partially modified or removed. Along with FT-IR data, the X-ray results confirmed the low content of lignin in the pulp samples by increasing the calculated values of the crystalline parameters. It was concluded that FT-IR spectroscopy can be used as a quick method to differentiate Eucalyptus globulus samples.