Hydroxypropylated lignins

The objective of this present work was to investigate the feasibility of using GPC/DV for absolute molecular weight determination of hydroxypropylated lignins. In order to verify the validity of the universal calibration method, vapor phase osmometry (VPO) was used to provide reference number average molecular weight values. Comparisons with LALLS results have also been made and will be reported in another publication. 

The results of the molecular weight determination of the hydroxypropy-lated lignins by VPO are shown in Table I. It may be noted that for all samples, there was about a 20% increase in apparent molecular weights between freshly prepared solutions and those tested three days later. It is postulated that such an increase was due to a time dependent association of the hydroxypropylated lignin molecules in solution. 

Kraft and steam explosion hydroxypropyl lignins (HPL) None D 15... 

Only one of the approaches considered here, chain-extension with propylene oxide of hydroxypropyl lignins, allowed for the preparation of networks with substantial elongation at break. Typical of most polyurethanes, an increase in the elongation at break resulted in a corresponding decrease in modulus and strength. This represents the most complex modification procedure of those discussed, although process development could probably simplify this modification for adoption on industrial scale. 

This paper examines two types of hydroxypropyl lignin based macromers, and these are illustrated schematically in Figure 1. Macromers with propylene oxide (PO) are formed by reducing the number of available hydroxyl groups on HPL followed by chain extension with PO and macromers with cellulose triacetate (CTA) are synthesized by attaching a monofunctional CTA chain to a limited number of terminal OH groups on HPL via a suitable grafting reaction. 

Materials. Hydroxypropyl lignin (HPL) Organosolv (aqueous ethanol) lignin from aspen, supplied by Repap Technologies Inc. (formerly the Biological Energy Corporation) of Valley Forge, PA, was hydroxypropylated by reaction with propylene oxide in the usual manner (9). This derivative was isolated and purified as described previously (9). 

Chain extension with PO Partially blocked hydroxypropyl lignin derivatives were reacted with propylene oxide in toluene, using KOH as catalyst, for the purpose of creating extended propyl ether chains. This has been reported elsewhere (13). 

Figure 1. Schematic representation of two types of hydroxypropyl lignin-based macromers.

Although techniques such as NMR spectroscopy can provide valuable information about the structure of hydroxypropyl lignins (4), we perceive a need for the development of synthetic methodology for model compounds which incorporate the structural features thought to be present in hydrox-ypropyl lignins. Such compounds can be used for studies of reaction kinetics as well as for confirming spectral assignments. 

Table I. Electron Impact Mass Spectral Fragmentation of Hydroxypropyl Lignin Model Compounds...

Figure 5. Hydroxypropyl lignin degradation and analysis scheme.

Compounds Identified in the VPC/MS Analysis of a Hydrogenated Hydroxypropyl Lignin... 

Bleaching of Hydroxypropyl Lignin with Hydrogen Peroxide... 

It was the intent of the present investigation to examine the one step bleachability of non-phenolic, water-insoluble hydroxypropyl lignin (HPL) derivatives with hydrogen peroxide in homogeneous phase (i.e., aqueous ethanol). 

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