Dataset on the structural characterization of organosolv lignin obtained from ensiled Poaceae grass and load-dependent molecular weight changes during thermoplastic processing

This article presents experimental data of organosolv lignin from Poacea grass and structural changes after compounding and injection molding as presented in the research article “Effects of high-lignin-loading on thermal, mechanical, and morphological properties of bioplastic composites” [1]. It supplements the article with morphological (SEM), spectroscopic (31P NMR, FT-IR) and chromatographic (GPC, EA) data of the starting lignin as well as molar mass characteristics (mass average molar mass (Mw) and Polydispersity (D)) of the extracted lignin. Refer to Schwarz et al. [2] for a detailed description of the production of the organosolv residue and for further information on the raw material used for lignin extraction. The dataset is made publicly available and can be useful for extended lignin research and critical analyzes.


Specifications
Value of the data • The data are convenient to examine the structural characteristics of organosolv lignin from herbaceous plants such as Poaceae grass and can be compared with other related studies. • The data establish a link between lignin content in bioplastic composites and load-dependent molecular weight changes. • These data allow other researchers to extend the characterization of lignin in highly-filled composites.

Data
Morphological characteristics of lignin from Poaceae grass are shown in Fig. 1. Molecular weight change upon solvent-extraction of the organosolv residue and molecular weight changes of lignin as a function of lignin loading in processed lignin bioplastic composites [1]. are given in Fig. 2. Data on lignin purity are given in Table 1.
Raw spectral data of the starting lignin are shown in Figs. 3 and 4 and band assignments and hydroxyl group contents are given in Tables 2 and 3, respectively.

Sample collection and preparation
A lignin-rich fraction was obtained by organosolvation of a grass silage press cake (PC) batch, described earlier by Schwarz et al. [2]. The obtained solid lignin phase was Soxhlet-extracted for 24 h using ethyl acetate (EtOAc), air dried overnight and then stored at ambient conditions until use.

Purity analysis
Lignin purity analysis was conducted according to NREL standard methods [11]. Acid insoluble lignin (Klason lignin) was examined by sulfuric acid hydrolysis. Residual carbohydrate and ash   1. a) and c) Scanning electron micrographs of a precipitated Poaceae grass lignin particle displaying the particle surface and b) and d) size distribution of precipitated lignin particles and size distribution of clustered particles on the particle surface obtained from image analysis. content were determined according to NREL/TP-510-48087 and sulfur content was determined using elemental analysis [12]. Measurements were run on vacuum-dried samples in duplicate and data are given as the arithmetic averages.

Fourier-transform infrared spectroscopy (FT-IR)
FT-IR analysis was performed to examine the starting lignin. Direct transmittance was measured by using the KBr pellet technique with a lignin concentration of 0.3 wt% in 300 mg KBr. The following parameters were used: spectral range: 400-4000 cm −1 , spectral resolution: 2 cm −1 , total scans: 128, background: KBr.

Morphological analysis
Mean lignin particle size and particle size distribution were evaluated using a scanning electron microscope operated at 10 kV and by image analysis.

31 P NMR
Spectral data were obtained according to a previously reported procedure and data on different functional groups present in lignin were obtained from integration of the spectra and calculated as described herein [13].

Gel permeation chromatography (GPC)
GPC was used to examine the mass average molecular weight and molecular weight distribution of isolated (starting) and processed lignin. For the determination of molecular weight changes following thermoplastic processing, lignin was Soxhlet-extracted for 24 h from ground composites using DMSO and lyophilized. The measurements were performed at 50°C using 0.075 M DMSO/LiNO 3 as the Table 1 Data on purity analysis of obtained Poaceae grass lignin: Mass average molecular weight, residual sugar, ash, sulfur content and mean particle size.

Molar mass
Purity Mean particle size