05 | 2010

Polyurethanes | Elastomers
New Biobased Polyurethane
from Lignin and Soy Polyols
M. Özgür Seydibeyoğlu
Manjusri Misra
Amar Mohanty
Bioproducts Discovery &
Development Centre
Department of Plant Agriculture,
University of Guelph,
Guelph, Ontario, Canada
Figure 1: Lignin Particles
(Electron Microscopy Images)
Lignin being the second most abundant polymer in the
world is undervalued which is a by-product in the pulppaper
and lignocellulosic industries [1]. Lignin with high
e-modulus value (5-6.7 GPa) offers many new materials as a
polymer and as a reinforcing phase. Lignin particles are shown
in Figure 1 (Electron microscopy Hitachi S-570 at 10 kV).
On the other side, biobased polyurethane materials take a lot
of attention to replace petroleum based polyurethanes (Figure
2 showing lignin incorporated polyurethane structure) [4].
Polyurethane has two important components, the isocyanate
and the polyol. These two reactants have many different forms
creating a wealth of different of products and applications.
Recent research is focused on replacing petroleum based
polyol with plant based polyols [5-7]. One of the most commonly
used polyol is the castor oil due its high hydroxyl numbers [6].
Another commonly used soy polyol is obtained from soybean
oils. However the use of soy polyol based polyurethanes is
limited due to lower mechanical properties. There are studies
to reinforce biobased polyurethanes with glass fibers and hemp
fibers to overcome the low mechanical properties [8, 9].
In this study, lignin was used as reinforcement for soy polyol
based polyurethanes. The lignin (Protobind 2400 from ALM
Private Limited, Hoshiarpur, Punjab, India) with a hydroxyl value
of 400 mg KOH/g was blended with soy polyol with hydroxyl value
of 166 mg KOH/g. Afterwards, the polyol blend was reacted with
different isocyanates at 150ºC and cured for 8 hours. Three
different isocyanates were used from Huntsman Chemicals,
PMDI (polymeric diphenyl methane diisocyanate (pMDI, Rubinate
M)), MDI (diphenyl methane diisocyanate, Rubinate 9511),
and modified MDI (Rubinate 9271). Tensile testing was done
to understand the ultimate strength, e-modulus and percent
elongation of the materials synthesized.
The lignin was incorporated at 5 wt % in soy polyol based
polyurethanes prepared with three different isocyanates. For
all the polyurethanes, the lignin showed reinforcing effect.
The tensile strength was improved by 70%, 57%, and 118% for
PMDI, MDI, and MMDI based polyurethanes respectively. The
percent elongation values were 13.50%, 87.30%, and 105.00%
respectively. Figure 3a and Figure 3b shows two different
polyurethanes obtained with lignin and soy polyol reacted with
different isocyanates representing different elongation values
obtained.
42 bioplastics MAGAZINE [05/10] Vol. 5