Cleavage of lignin model compounds and ligninox using aqueous oxalic acid

Article abstract of DOI:10.1039/c9ob01452g

Aqueous oxalic acid cleaves oxidised β-O-4 lignin model compounds by two distinct mechanisms that are dependent on the presence of the hydroxymethyl substituent. Various β-O-4 phenoxyacetophenones that do not contain the hydroxymethyl substituent undergo oxidative cleavage upon exposure to aqueous oxalic acid in the presence of air, likely through concerted ring opening of a dioxetane intermediate to give the corresponding benzoic acid and phenyl formate. Importantly, detrimental side reactions arising from singlet oxygen and hydroperoxy radicals (from both O₂ and oxalic acid) are minimal when the cleavage is run under air compared to neat oxygen. When oxidised β-O-4 lignin model compounds bearing the hydroxymethyl group are cleaved by aqueous oxalic acid, the resulting diketone and phenol products arise from a redox neutral cleavage that is analogous to the formic acid-sodium formate mediated lignin cleavage process reported by Stahl. Aqueous oxalic acid also cleaves lignin itself, with oxidised milled wood lignin (MWL^ox) from Pinus radiata giving a 14% yield of ethyl acetate soluble aromatics with good selectivity for vanillin. Aqueous oxalic acid appears to be a promising lignin cleavage system given the benign, bio-based reagents, absence of metals and organic solvents and a simple extraction procedure that enables oxalic acid recycling.

Full text of DOI:10.1039/c9ob01452g

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Page 1 of 22
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ox
Cleavage of Lignin Model Compounds and Lignin using
D
A
OI
q
: 10
u
.10
e
3
o
9/C9OB01452G
u
s
Oxalic Acid
a
b
a
Ashley C. Lindsay, Shinji Kudo and Jonathan Sperry *
a
Centre for Green Chemical Science, University of Auckland, 23 Symonds Street, Auckland,
New Zealand
b
Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasuga Koen,
Kasuga 816-8580, Japan
E-mail: j.sperry@auckland.ac.nz

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DOI: 10.1039/C9OB01452G
Abstract
Aqueous oxalic acid cleaves oxidised β-O-4 lignin model compounds by two distinct
mechanisms that is dependent on the presence of the hydroxymethyl substituent. Various β-O-
4
phenoxyacetophenones that do not contain the hydroxymethyl substituent undergo oxidative
cleavage upon exposure to aqueous oxalic acid in the presence of air, likely through concerted
ring opening of a dioxetane intermediate to give the corresponding benzoic acid and phenyl
formate. Importantly, detrimental side reactions arising from singlet oxygen and hydroperoxy
radicals (from both O and oxalic acid) are minimal when the cleavage is run under air
2
compared to neat oxygen. When oxidised β-O-4 lignin model compounds bearing the
hydroxymethyl group are cleaved by aqueous oxalic acid, the resulting diketone and phenol
products arise from a redox neutral cleavage that is analogous to the formic acid-sodium
formate mediated lignin cleavage process reported by Stahl. Aqueous oxalic acid also cleaves
ox
lignin itself, with oxidised milled wood lignin (MWL ) from Pinus radiata giving a 14% yield
of ethyl acetate soluble aromatics with good selectivity for vanillin. Aqueous oxalic acid
appears to be a promising lignin cleavage system given the benign, bio-based reagents, absence
of metals and organic solvents and a simple extraction procedure that enables oxalic acid
recycling.

Page 3 of 22
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DOI: 10.1039/C9OB01452G
Introduction
The vast majority of carbon-based chemicals manufactured within the global chemical industry
1
are derived from finite fossil reserves . A sustainable alternative to current practise will involve
biorefineries processing renewable biomass into valuable base chemicals that can replace those
1
-3
currently sourced from non-renewable resources . The main feedstock in these biorefineries
will be lignocellulosic biomass (dry plant matter) that consists of cellulose (35-50%),
4
hemicellulose (20-35%) and lignin (10-25%) . Lignin, an excellent potential source of bio-
based aromatic compounds, is a robust, amorphous biopolymer made up of phenylpropanoid
units randomly linked via several distinct C-O and C-C crosslinks that render the biopolymer
resistant to depolymerisation (Figure 1)3, 5-13. The most abundant linkage within lignin is the β-
O-4 alkyl aryl ether (ca 50% of linkages in both soft and hardwood), efficient cleavage of
which is vital its depolymerisation8, 12, 14-21
.
OMe
O
O
MeO
O
HO
OH
O
MeO
MeO
O
OH
OMe
O
MeO
HO
OH
O
OH
MeO
OH
HO
O
O
O
O
O
OMe
OH
OH
O
HO
MeO
HO
OH
O
MeO
OMe
MeO
O
HO
HO
O
O
HO
O
O
OMe
HO
OH
OMe
O
MeO
OMe
O
Figure 1: Representative lignin structure highlighting β-O-4 aryl ether linkage (red).

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A common strategy for cleavage of the β-O-4 linkage involves an initial oxidation to give the
DOI: 10.1039/C9OB01452G
β-O-4 phenoxyacetophenone 1, and subsequent C-O bond scission17, 18, 21. The oxidation step
results in a decrease in the dissociation enthalpy of the C-O aryl ether bond, allowing for more
2
2
mild cleavage conditions to be subsequently employed . Existing methods for the cleavage
of oxidised β-O-4 phenoxyacetophenone system 1 include a variety of reductive23-29
,
oxidative30-40 and catalytic processes41-50 that yield different aromatic cleavage products
depending on conditions used (Scheme 1).
Scheme 1: Oxidation of the β-O-4 linkage and cleavage of the resulting β-O-4
phenoxyacetophenone under reductive23-29, oxidative30-40 and catalytic conditions41-50
.
Many of the cleavage methods outlined in Scheme 1 use organic solvents23, 25, 30, 32, 37, 38, 44-48
including acetonitrile27, 36, 41-43, 50, n-hexanes26 toluene31 and ethyl acetate24 that present
environmental and safety concerns, particularly on large scale51
methods require flammable hydrogen gas23-27, often at high pressure24, 26, 28 and temperature
,
.
Existing reductive cleavage

Page 5 of 22
Organic & Biomolecular Chemistry
150-275 °C)23-28, in the presence of transition-metal catalysts23-29. Catalytic approaches use a
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DOI: 10.1039/C9OB01452G
(
range of transition-metal photocatalysts41, 42, 44-46, 50, porous organic frameworks and catalysts
43
4
7
30-40
require transition-metal catalysts30-32,
based on palladium . Current oxidative procedures
3
6, 40
33
30.
and can feature undesirable additives such as H
3
PO
4
and BF
3
·OEt
2
A valuable addition to the existing methods outlined in Scheme 1 would be a cheap, robust
40
cleavage protocol that is mediated by air at atmospheric pressure and free from both organic
solvent and metals. Our preliminary proposal towards this goal is shown in Scheme 2. The
diacid oxalic acid would mediate the enolisation of the phenoxyacetophenone system 2 under
aqueous conditions to give 3 that upon reaction with the oxygen present in air would undergo
C-O bond cleavage30-39 to the corresponding phenol (4) and benzoic acid (5). Oxalic acid is a
good candidate for large scale lignin depolymerisation as it is a low cost, water soluble
crystalline solid that is stable at room temperature52, 53. It is fully biodegradable, natural
compound that is industrially manufactured through the oxidation of carbohydrates from
biorenewable feedstocks such as sugar, reclaimed starch and molasses, with a world-wide
5
2
manufacturing capacity currently in excess 150,000 tonnes per annum . A recent report
detailing the production of oxalic acid by hydrogenation of carbon dioxide emphasises its
54
potential as a readily accessible, biobased reagent for future industrial processes .
Furthermore, the fractionation of lignocellulosic biomass into hemicellulose sugars, cellulose
pulp and lignin using the oxalic acid-based OrganoCat process further highlights the potential
of oxalic acid in biomass processing55, 56
.

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DOI: 10.1039/C9OB01452G
Scheme 2: Proposed metal and organic solvent-free oxidative cleavage of the β-O-4 linkage
Results and Discussion
We set out to examine the proposal in Scheme 2 and began by subjecting the β-O-4 model 6 to
aqueous oxalic acid in the presence of air (Table 1). Treating the model 6 with a 0.02 M aqueous
solution of oxalic acid at 100 °C gave trace amounts of p-anisic acid (7) (entry 1). Increasing
the concentration of oxalic acid to 1 M and 2 M did not improve the yield of the cleavage
product 7 (entry 2 and 3). Gradually increasing the concentration of oxalic acid (3-16 M)
increased the yield of 7 to 73%, also resulting in the isolation of guaiacol (8) in all cases (entries
4
-7). The instability of guaiacol (8) under oxidative conditions30, 57, 58 explains the low yield in
this instance. When no oxalic acid was present, only trace amounts of 7 were observed, clearly
indicating oxalic acid is vital for the cleavage reaction (entry 8). When the cleavage was
conducted under nitrogen gas, the reaction stalled after 24 h, indicating that the oxidative
conditions were indeed essential for efficient cleavage (entry 9). However, when the cleavage
reaction was run under an oxygen atmosphere, the yield of p-anisic acid (7) greatly reduced
and p-acetanisole (9) was formed (entry 10). This unexpected result suggested there was more
than one mechanism operating in this process. Indeed, the oxidative cleavage of β-O-4 linkages
5
9
30,
mediated by O has been proposed to occur through singlet oxygen , radical intermediates
2

Page 7 of 22
Organic & Biomolecular Chemistry
3
2, 33, 36
34
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DOI: 10.1039/C9OB01452G
or direct reaction with oxygen . In order to decipher the mechanism(s) underpinning
this cleavage reaction, a detailed mechanistic study was performed. First, the singlet oxygen
60
generator Rose Bengal was added to the cleavage reaction under an oxygen atmosphere in
under ambient light conditions and in the presence of a desk lamp (entries 11-12). These
conditions slightly reduced the yield of 7, but led to a slight increase in yield of p-acetanisole
5
9
(
9) . When Rose Bengal was added to reaction under air, the cleavage was significantly
inhibited (entry 13). The combination of these results indicate that the formation of 9 is likely
occurring through a singlet oxygen mediated process that is most prevalent when a pure oxygen
atmosphere is present. Next, in order to determine if the formation of 7 and 8 proceeded through
a radical pathway, the radical scavenger (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)34
was added to the reaction under an air atmosphere, which led to no significant effect on the
yield (entries 7 vs 14). This suggests that the formation of 7 and 8 does not occur via a radical
mediated process; indeed, the addition of TEMPO under an oxygen atmosphere led to an
increased yield of p-anisic acid (7) in a much faster reaction time (entry 15). This result is likely
due to the quenching of hydroperoxy radicals30, 32, 33, 36 photolytically formed under an oxygen
atmosphere that are otherwise detrimental to the cleavage reaction (entries 10 v 15). Next, we
set out to investigate if oxalic acid, which is known to undergo degradation in the presence of
oxygen and light to produce hydrogen peroxide (and hence hydroperoxy radicals) and carbon
61
dioxide , was detrimental to the reaction. Thus, the cleavage reaction was conducted in the
dark, and in the presence of a desk lamp, to hinder and promote H production from oxalic
2
O
2
acid, respectively. When the cleavage was run in the dark, the yield of p-anisic acid (7) was
significantly increased compared to ambient light conditions (entries 10 and 16) and only trace
amounts of p-acetanisole (9) were observed. When a desk lamp was shone onto the reaction, a
reduced yield of p-anisic acid (7) was observed that was more in agreement with the initial
surprising result (entries 10 and 17). These results infer that oxalic acid undergoes a light-O
2

Organic & Biomolecular Chemistry
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6
1
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DOI: 10.1039/C9OB01452G
mediated degradation into hydrogen peroxide and hydroperoxy radicals that are detrimental
to the cleavage, and that this process is most noticeable when the reaction is run under an
oxygen atmosphere. Indeed, when hydrogen peroxide was added under controlled conditions,
the yield of 7 was significantly reduced (entry 18). Based on all of the data in Table 1, it is
interesting to note that running this cleavage under neat oxygen leads to undesired side
reactions and the lower oxygen content in air is actually beneficial for this process.

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DOI: 10.1039/C9OB01452G
Table 1: Oxidative Cleavage of β-O-4 Model 6
Desk
a
Time
h)
Product
Oxalic acid
Entry
Atmosphere
Additive
-
1
Lamp
(
molL )
(
and yield
(
42W)
1
2
3
4
5
6
7
8
9
0.02
1
120
96
48
24
24
24
24
120
24
10
air
air
air
air
air
air
air
air
-
-
-
-
-
-
-
-
-
-
-
-
7 (trace)
7 (trace)
-
2
-
7 (trace)
3
-
7 (20%), 8 (11%)
7 (29%), 8 (11%)
7 (53%), 8 (18%)
7 (73%), 8 (10%)
7 (trace)c
4
-
8
-
16b
-
-
-
16
16
N
O
O
2
2
2
-
7 (15%)d
1
1
0
1
-
7 (29%), 9 (5%)
2
4
Rose Bengal
7 (16%), 8 (25%), 9
16
16
(
9%)
2
4
O
2
Rose Bengal
Yes
7 (20%), 8 (20%), 9
8%)
1
2
(
1
1
1
1
3
4
5
6
16
16
16
16
24
30
6.5
22
air
air
Rose Bengal
TEMPO
TEMPO
-
-
-
-
7 (4%), 8 (8%)
7 (68%), 8 (11%)
7 (80%), 8 (9%)
7 (80%), 9 (trace)
O
O
2
2
DARK
Yes
1
1
7
8
16
16
24
24
O
2
-
7 (44%), 9 (trace)
7 (36%), 8 (6%)
Air
H
2
O
2
DARK
a
b
-1
c
Oxalic acid dihydrate; 16 molL = 21 equivalents; reaction abandoned after 5 days with only trace amounts
d
of 7 observed; reaction stalled with no further cleavage occurring.

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Based on the study outlined in Table 1 ruling out both singlet oxygen and radical mediated
DOI: 10.1039/C9OB01452G
cleavage mechanisms when air is used, we proceeded to develop a plausible mechanistic
scenario for the formation of 7 and 8 from model 6. We initially set out to investigate if the
mechanism was akin to that reported by Han, who identified the intermediate glyoxal 10 during
the oxidative cleavage of 2-phenoxyacetophenone (2) into phenol (4) and benzoic acid (5)
3
4
catalysed by the ionic liquid [OMIm][OAc] (Scheme 3, A) . Attempts to synthesise the
putative glyoxal intermediate 11 from both p-acetanisole (9) and 2-hydroxy-4'-
methoxyacetophenone (12) using a variety of oxidative conditions62-67 led to only p-anisic acid
(
7), presumably resulting from the decarboxylation of the intermediate glyoxal 11 (Scheme 3,
B). The facile nature of this decarboxylation under oxidative conditions implies that glyoxal
1 could be an intermediate in this cleavage reaction; however, when the putative glyoxylic
1
acid intermediate 13 (also proposed by Han, Scheme 3, A) was subjected to our cleavage
conditions, p-anisic acid (7) was not formed, inferring the cleavage (ie, the formation of 7 from
6
) does not proceed via a glyoxylic acid intermediate 13.

Page 11 of 22
Organic & Biomolecular Chemistry
O
O
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DOI: 10.1039/C9OB01452G
A
[OMIm][OAc], O2
H O, 373 K
OH
O
2
+
HO
2
4
5
[
OMIm][OAc]
O
H2O
O2
O
H
HO
[
O]
O
O
glyoxal 10
glyoxylic acid
B
O
DMSO/H O
2
HO
or IBX
O
OMe
O
12
H
76-100%
O
HO
O
OMe
Me
OMe
glyoxal 11
not observed
SeO or KMnO
2
4
7
OMe
9
O
KOH, KMnO4
oxalic acid, H O
2
HO
H O, rt, 16 h
2
100 °C, 48 h
O
45%
OMe
glyoxylic acid 13
3
4
Scheme 3: A) Han’s proposed mechanism , B) Investigation of key intermediates 11 and 13
Based on all the results accumulated thus far, a plausible mechanistic scenario for the oxidative,
oxalic acid-mediated cleavage can be proposed (Scheme 4). An initial acid mediated
enolisation of 6 occurs to give 14; reaction with molecular oxygen generates an unstable
6
8
dioxetane intermediate 15 that could potentially fragment via two pathways . In pathway A,
ring opening of 15 gives hydroperoxide 16 which, after reduction to alcohol 17 (potentially
6
9
mediated by oxalic acid ), proceeds through an acid-mediated C-O bond cleavage to yield
guaiacol (8) and glyoxal 11. Attack of water, subsequent loss of formic acid to anisaldehyde
70
(
18) and oxidation would give p-anisic acid (7) . Alternatively, in pathway B, dioxetane 15
7
1
undergoes C-C bond cleavage through a concerted ring opening to give p-anisic (7) and
phenyl formate 19, the later undergoing facile cleavage the under acidic reaction conditions72
to give guaiacol (8). In a control experiment, anisaldehyde (18) did not convert into p-anisic

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acid (7) under the cleavage conditions, suggesting pathway B is operating. The formation of p-
DOI: 10.1039/C9OB01452G
acetanisole (9) is likely a result of singlet oxygen induced C-O bond cleavage, which has been
reported to proceed via initial reaction of singlet oxygen with the acetophenone ring in 659
.
OMe
OH
OMe
O
O
O
H+
H
6
9
OMe
OMe
O
1O
O
2
HO
O
OMe
OH
O2
O
14
OMe
OMe
O
OMe
OH
O
O
Pathway A
O
OOH
OMe
O
16
15
OMe
reduction
O
Pathway B
OMe
H
O
O
H
O
H+
OH
OMe
O
H O
2
17
HO
+
-HCOOH
OMe
OMe
7
19
O
OH
O2
H
O
+
OMe
O
H
8
OMe
11
OMe
H2O
O
18
O
HO
H
O
1,2-shift
-
HCO H
HO
2
OH
H+
OMe
OMe
Scheme 4: Proposed mechanism of oxidative oxalic acid-mediated cleavage of 6
With a plausible mechanism established, the optimised cleavage conditions were examined on
a number of other β-O-4 lignin model compounds (20-25, Table 2). These conditions proved
to be successful, with good to moderate yields of the corresponding carboxylic acid cleavage
products obtained in all instances. Moreover, this procedure does not require traditional

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extraction based work-up procedures. Upon cooling, oxalic acid dihydrate crystallises from the
DOI: 10.1039/C9OB01452G
reaction mixture, and the desired cleavage products can be simply washed with ethyl acetate
from the resultant crystals. The residual oxalic acid can be reused in the cleavage three times
with no reduction in yield (see supporting information).
Table 2: Cleavage of phenoxyacetophenone lignin model compounds with aqueous oxalic acid
ox
Lignin Model Compounds
Product(s) and yield
1
2
5
3
4
2
2
2
0: R =R =R =OMe; R =R =H
-
7 (67%)
7 (60%)
27 (85%)
7 (27%)
27 (57%)
27 (37%)
3
5
1
2
4
1: R =R =OMe; R =R =R =H
26 (10%)
3
4
5
1
2
2: R =R =R =OMe; R =R =H
-
5
1
2
3
4
2
2
2
3: R =OMe; R =R =R =R =H
-
2
4
5
1
3
4: R =R =R =OMe; R =R =H
-
1
2
4
5
3
5: R =R =R =R =OMe; R =H
28 (22%)
With the successful cleavage of phenoxyacetophenone models 20-25 achieved, we anticipated
that the same conditions could also cleave oxidised β-O-4 models of type 29 bearing a
hydroxymethyl substituent (Scheme 5). Based on Stahl’s pioneering, redox neutral cleavage of
lignin models using sodium formate-formic acid,53, 73 we anticipated an initial oxalylation of
7
4
2
9 would lead to 30. Upon E1H-3c4e elimination of 30 to enol 31, tautomerisation and
hydrolysis would deliver diketone 32 and phenol 4.

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Scheme 5: Proposed oxalic acid-mediated cleavage of oxidised hydroxymethyl model 29 based
on the work of Stahl
The oxalic acid conditions proved to be successful on a variety of oxidised hydroxymethyl β-
O-4 models 33-38, with good to excellent yields of the diketones 39-40 isolated in all examples
(
Table 3). Variable yields of the phenol component 26, 28 and 8 were also observed, in line
with their reported instability under acidic conditions. The isolation of diketones 39-40 and
phenols 26, 28 and 8 infers that the cleavage is occurring by an analogous redox neutral
mechanism reported previously.57, 74

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Table 3: Cleavage of oxidised hydroxymethyl containing β-O-4 models with aqueous oxalic
acid.
ox
Lignin Model Compounds
Product(s) and yield
1
2
5
3
4
3
3
3
3
3
3
3: R =R =R =OMe; R =R =H
26 (100 %)
39 (91 %)
39 (98 %)
40 (86 %)
40 (54 %)
40 (54 %)
39 (100%)
3
5
1
2
4
4: R =R =OMe; R =R =R =H
28 (27 %)
-
3
4
5
1
2
5: R =R =R =OMe; R =R =H
2
4
5
1
3
6: R =R =R =OMe; R =R =H
8 (22 %)
26 (39 %)
8 (70 %)
1
2
4
5
3
7: R =R =R =R =OMe; R =H
2
5
1
3
4
8: R =R =OMe; R =R =R =H
With the cleavage of several β-O-4 model systems successfully developed, the
depolymerisation of lignin was investigated. Milled wood lignin (MWL) from Pinus radiata,
7
5
the fast growing tree at the core of the New Zealand forestry industry , was pre-washed with
ethyl acetate and subjected to the oxalic acid cleavage conditions, which resulted in a 4 wt%
1
yield of ethyl acetate soluble aromatics, along with an insoluble char-like by-product. H HSQC
NMR of the char showed the disappearance of key lignin linkages, indicating the
depolymerisation of the biopolymer, albeit in poor yield (Figure 2, A vs B). The cleavage was
ox
subsequently examined on oxidised Pinus radiata MWL (MWL ). Oxidation of the MWL
2
2
using DDQ was successful, as shown through the disappearance of C-Hα along with the
1
corresponding appearance of the ketone structure in A` in the H HSQC NMR (Figure 2, A vs
ox
C). Subsequent cleavage of the pre-washed MWL under our optimised conditions gave a 14
wt% yield of ethyl acetate soluble aromatics, along with char. The loss of key linkages evident

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1
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DOI: 10.1039/C9OB01452G
by H HSQC NMR analysis demonstrated successful depolymerisation (Figure 2, C vs D). The
1
ox
H NMR of the soluble fraction from MWL showed the cleavage had proceeded with good
selectivity, with vanillin identified as the major product (Figure 2, E), as supported by GC-MS
analysis (see supporting information). The production of vanillin from the cleavage of the
ox
MWL is interesting. Vanillin may form upon formylation of guaiacol by the formic acid
produced during the cleavage (see Scheme 4). Additionally, the oxidation step proposed in
Scheme 4 (18 --> 7) may not operate on the real biopolymer system, instead resulting in
vanillin.

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Figure 2: Partial 2D HSQC NMR spectra (DMSO-d ) of: A) Pinus radiata MWL; B) Pinus
6
radiata MWL after oxalic acid mediated cleavage; C) oxidised Pinus radiata MWL; D)
oxidised Pinus radiata MWL after oxalic acid mediated cleavage. Cross peaks are colour coded
ox
to corresponding key lignin linkages. Reaction conditions: MWL or MWL , oxalic acid (16
1
M), air, 100 °C, 4 h; E) Partial H NMR spectra (DMSO-d
6
) of the ethyl acetate soluble fraction
ox
from the cleavage of MWL (top) versus MWL (bottom). Relevant GPC traces are available
in the supporting information

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DOI: 10.1039/C9OB01452G
Conclusions
The hydroxymethyl substituent on β-O-4 lignin models dictates the mechanism by which they
undergo cleavage in aqueous oxalic acid. β-O-4 models that do not contain the hydroxymethyl
substituent undergo oxidative cleavage in the presence of air, whereas models bearing the
hydroxymethyl group undergo a redox neutral cleavage that is analogous to the formic acid-
sodium formate cleavage process reported by Stahl.52,68 It was also shown that aqueous oxalic
ox
acid cleaves oxidised milled wood lignin (MWL ) from New Zealand Pinus radiata to give a
1
4% yield of ethyl acetate soluble aromatics with good selectivity for vanillin. Advantages of
this cleavage procedure include; (i) the use of benign reagents, oxalic acid and water, with air
as the oxidant; (ii) the absence of any metals and organic solvents; (iii) a simple extraction
procedure that enables oxalic acid recycling. Examination of these cleavage conditions on
various lignin biopolymers are currently underway in our laboratory.
Acknowledgements
We thank the University of Auckland for support though the Faculty Research Development
Fund (FRDF). We thank Dr Ian Suckling (Scion, NZ) for providing the Pinus radiata milled
wood lignin.

Page 19 of 22
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