Lignin polyols

Reactions of alkoxylated lignin with diisocyanates produce thermoset materials because the lignin polyol is always polyfunctional with a functionality greater than 2. The isocyanate-alcohol reaction produces a urethane linkage that when repeated creates a crosslinked, nonreformable polyurethane. This is shown in Fig. 6. A broad spectrum of lignin-based urethanes have been made and tested. The data show that these materials match if not exceed the properties of synthetic polyurethanes made without lignin [60]. 

Property Kraft Lignin Polyol Hydrolyzed Copolymer Polyol Unhydrolyzed Copolymer Polyol... 

MeadWestvaco USA Non-sulfonated kraft lignin, lignosulfonates Lignin products hydroxymethylated lignin, propoxylated lignin polyols additives for cements and animal feeds Adhesives for particle boards Wax emulsifier Dispersants for dyes and pigments, ceramics, refractories and concrete... 

In this section, PU composites are designed using plant components in both matrix and filler, i.e. two types of lignin-polyol derived from KL and LS are used to prepare polyurethane matrix and wood powder as fillers [165, 166]. In order... 

Lignin polyols were prepared using KL or LS which was solved in DEG, TEG, or PEG. In order to control the reaction, polyols obtained from ML were also added. Figure 42 shows examples of PU composites derived from LSP/MLP, 50/50 mixture, filled with A1 (011)3. The mixing ratio of A1 (011)3 is shown as wt% in total polyol. The dark brown colour comes from colour of LS. 

Polyurethanes (PU s). SL and 4,4 -diphenylmethane diisocyanate (MDI) were dissolved in tetrahydrofuran (THF), and the solution was stirred for 1 hr at 60°C. A THF solution of polyethylene glycol (PEG 400) and diethyl bis(2-hydroxyethyl)aminomethylphosphonate (polyol containing phosphorous) was added to the reaction mixture, and the reaction time was extended for 1 hr. In all reactions, the molar ratio of the total amount of isocyanate groups to the total amount of hydroxyl groups (NCO/OH) was maintained at 1.2. The lignin content in PU was 20 wt%. Each solution was drawn on a glass plate, and allowed to dry for 48 hr. The residual solvent in a sample was removed under vacuum and curing of each PU film was carried out at 120°C for 3 hr under a pressure of 50 kg/cm2. 

Table II shows the correlation of wt% of polyol containing phosphorous in PU with 20 wt% of lignin with oxygen indices which were obtained according to the procedure of JIS method. In this method, the inflammability of a sample is tested in a mixture of oxygen and nitrogen under a constant flow rate of the mixture. The oxygen index is the minimum concentration of oxygen in which a sample is inflammable. The oxygen index for PU without phosphorous and those for PU s with phosphorous are 19.3 and 24.6, respectively. That is, qualitatively, PU s with phosphorous were not inflammable in air and PU without phosphorous was inflammable. This indicates that PU becomes less inflammable by the addition of 3 wt% of polyol containing phosphorous.

Figure 5. TG curves for polyurethanes (PU s) (containing 20 wt% of lignin) prepared with polyol containing phosphorous measured in air. Number indicated for each line shows the content of polyol with phosphorous expressed in wt%. Heating rate 10°C/min. Flow rate 15 ml/min.

From the results obtained in this study, it is concluded that lignin in PU s retards the thermal degradation of PU s in air and also that PU s containing lignin become nonflammable in air with the addition of a polyol containing phosphorous. 

Although the use of lignin as an additive to polyurethanes is not new (15-20), even the most judicious selection of lignin isolation or modification schemes has not allowed researchers to overcome the incorporation limit of 25 to 40 weight percent of lignin as an active component in polyurethanes. Solvent fractionation allows for the isolation of lignin fractions with well defined solubilities and functionalities (21,22). Both of these features are critical for the practical inclusion of lignin into liquid polyol systems. 

Materials. The materials are described in detail in the studies summarized in Table I. Most of these results are based on kraft lignin. The NCO/OH ratio of all of these networks were high greater than 1.5. All of the networks were prepared from homogeneous solutions of the lignin-based polyol, added (soft segment) polyol, and diisocyanate. Films were cast and cured under mild conditions with a controlled loss of solvent. The films were post-cured to insure complete reaction (25). 

Various types of lignin-derived polyurethane products and their precursors appeared to satisfy these constraints. This paper summarizes experimental efforts aimed at developing lignin-derived polyol, polyisocyanate, and polyurethane products. 

Li.Qnin-VQJu.vzd PoLyoLi. Polyhydroxy (polyol) components may be prepared from lignin using a one-, two-, or three-step modi-... 

Low copolymer to propylene oxide ratios make it obviously difficult to totally liquefy lignin, Table II. Such conditions, however, seem to favor polyols with low total hydroxyl numbers. The oxyalkylation reaction appears to require catalyzation by zinc chloride or base catalysts in concentrations of about 10% or less for successful completion. The presence of an initiator (ethylene glycol) helps completion of the reaction in particular when the unhydrolyzed copolymer is used as substrate (Table III). 

The degree to which physical properties of polyols depend on the nature and prior treatment of the lignin employed in the oxyalkylation reaction is indicated in Table IV. Polyols pre-... 

Polyol Functionality in Relation to Method of Preparation--Ratio of Lignin Copolymer to Propylene Oxide (All Reactions 4 hrs. reaction time temperature 200-250°C)... 

Lignin Preparation Initiator (%) Catalyst (V> OH Number COOH Number Polyol Yield1 ... 

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