Soluble matter lost, = [conditioned weight − reconditioned weightconditioned weight] × 100
In addition to panels containing no polyglu- caramide, two additional controls were used in
this test. One was a pressed panel containing only the polyvinyl alcohol Airvol 203S used in the
pressed test panels. The other sample was a stan- dard fiber-reinforced test panel containing 24
soft wood fiber, 24 hard wood fiber, 19 a-cel- lulose and 33 filler other agricultural fibers.
This panel is typical of agricultural fiber-based composite panels that need to be coated with
water-resistant materials.
3. Results and discussion
3
.
1
. Synthesis of poly glucaramides
The results of the polymerization are summa- rized in Table 1. The yields were generally in the
range of 45 to 75. The one exception was the trioxa
polymer, poly4,7,10-trioxatride-
camethylene
D
-glucaramide where the yield was only 14. The melting points of the resultant
polymers were typically between 209 and 213°C. The only exception was polytetramethylene
D
- glucaramide at 195°C in which the short chain
length of the diamine component contributes to a lower melting point. X-ray powder patterns Fig.
2 showed that the synthesized polyglucaramides were semicrystalline polymers with between 40
and 50 crystallinity.
The synthesis of the polyglucaramides has been found to be simple, efficient and versatile.
The initial step in the path to polyglucaramides is the production of
D
-glucaric acid obtained from
D
-glucose. This reaction occurs readily by oxida- tion of
D
-glucose with concentrated nitric acid. This step limits the overall efficiency of the entire
production of polyglucaramides from glucose to polymer. The reason for this is the temperature
increase during the oxidation. If the temperature increases beyond 60°C, the glucose decomposes
rather than being oxidized. The use of N
2
bub- bling Kiely et al., 1997 in the system prevents
the drastic increase in temperature. In addition, we found that placing the reaction flask in an ice
bath during the initial stage of the oxidation further reduced the extent of glucose degradation.
After stabilization of the mixture, the reaction was returned to the 45°C water bath for the
duration of the oxidation.
D
-glucaric acid was obtained in 55 yield from the reaction. Interest-
ingly, when the oxidation was scaled to 50 and 300 g of glucose, the yield increased to 60 and
79 respectively. Thus, it seems from this study that larger batches are feasible, an important fac-
tor in the commercialization of this technology.
The polymerization reaction is likewise facile and proceeded without complication. The poly-
merization also demonstrates the versatility of the synthesis. Virtually any diamine could be used to
produce a polyglucaramide depending on the desired properties of the final polymer. In the
present study, the nonlinear diamines, 2-methyl- 1,5-pentanediamine and 1,3-diaminopentane, did
not yield solid polymers. While these products may be useful for some applications, they did not
suit the needs of the present project, which was based on mixing solid polymers and pressing them
into panels. As a result, these polymers were not fully characterized. Also, compounds with multi-
ple primary amino groups could be used in the polymerization, assuming proper stoichiometric
control of both monomers. For example, the use of a triamine should enable a network polymer
structure to be formed.
Hoagland 1981; Hoagland et al. 1987 has suggested that aminolysis reactions of aldaric
acids, diacids, such as glucaric acid which are derived from the oxidation of carbohydrates, de-
pend on a base-catalyzed lactonization followed by aminolysis of the lactone. Thus, the activation
of aldaric acid diesters results from the formation and inherent reactivity of these lactones. Kiely
and Lin 1989 reported that glucaric acid is typi- cally generated as a mixture of the pure acid form,
a multiple acid-lactone, and a dilactone. However, the product of the esterification is not critical and
any mixture can be used for polymerization. Thus, the polymerization mechanism of glucaric
acid with diamines involves the formation of a lactone of esterified glucaric acid followed by
aminolysis by the diamine. The inclusion of tri-
ethylamine in the reaction ensured that the poly- merization environment was sufficiently alkaline
to continue lactonization throughout the polymer- ization. Other studies Kiely and Chen, 1994;
Chen and Kiely, 1996 were specifically directed toward the synthesis of lactones of esterified glu-
caric acid in order to increase polymerization efficiency. Our goal was to keep the system as
simple as possible with for potential commercial applications. From the results of the polymeriza-
tion, it is evident that the triethylamine was suffi- cient to promote the formation of glucaric acid
lactones to produce adequate polyglucaramides with desirable properties.
One of the objectives of this project was to investigate
the commercial
applicability of
polyglucaramide production from starch as a renewable source for the glucaric acid monomer.
The conversion of starch to glucose is readily accomplished Lloyd and Nelson, 1992. How-
ever, to commercialize polyglucaramides, large quantities of the polymers must be economically
produced. To date, polyglucaramides have only been produced on a relatively small scale. In
previous studies Kiely and Chen, 1994; Kiely et al., 1994; Chen and Kiely, 1996 polyglu-
caramides were made in batches of less than 10 g. In this study, polyglucaramides were produced
in 100 g batches. The commercial demand for nylon resin excluding nylon fiber is currently
over half a billion kg per year with approximately 5 annual growth predicted. Nylon 6,6 resin cur-
rently sells for between 1.10 and 1.30kg. The cost of glucose is about 0.26kg which indicates
that polyglucaramides could compete economi- cally with nylon. Another factor to consider is
that the properties of the polyglucaramides must to be optimized to fit into specific applications. As
with other polymers from renewable resources, their physical properties must match or exceed
those of polymers already in use in order to be accepted commercially. With the versatility avail-
able in the chemistry of the production of polyglucaramides, these polymers could be pro-
duced in quantities competitive with commercial nylon resins although it is likely that they will be
used for different end-use applications.
3
.
2
. Mechanical testing of fiber-reinforced panels Mechanical testing was performed in order to
assess whether there was any increase in the strength of the pressed composite panels due to
the incorporation of the polyglucaramides. Table 2 shows the effect on tensile strength and
Young’s modulus of an increase of polyglu- caramide. Panels with polyoctamethylene
D
-glu- caramide showed an increase in tensile strength
proportional to an increase in polyglucaramide content. A binomial regression analysis of the
data gave an R
2
value of 0.982. For panels con- taining polydecamethylene
D
-glucaramide, ten- sile
strength reached
a maximum
at a
concentration of 33 – 37 determined by bino- mial regression analysis; R
2
= 0.774 and a further
increase in polyglucaramide corresponded to a decrease in tensile strength. Similar behavior was
seen for Young’s modulus. Panels containing polyoctamethylene
D
-glucaramide showed an in- crease in Young’s modulus proportional to an
increase in polyglucaramide content R
2
= 0.618. For panels containing polydecamethylene
D
-glucaramide, it again appeared that there was a maximum in Young’s modulus at between 33
and 37 of the polyglucaramide R
2
= 0.456. It
is not clear from the experiment why there was a difference in the behavior of the polyoc-
tamethylene
D
-glucaramide versus polydeca- methylene
D
-glucaramide. The inclusion of polyglucaramides in the pan-
els did not correspond to an improvement in the strength of the test panels. Thus, the primary
advantage of polyglucaramides in a pressed panel formulation is to impart water resistance.
3
.
3
. Water resistance of fiber-reinforced panels Results of the water resistance measurements of
the panels are presented in Table 3. Because the polyglucaramides chosen are water-insoluble it
was expected that they would impart some degree of water resistance to the panels. The control
containing only polyvinyl alcohol dissolved in the water during the immersion phase of the test.
The other control, containing several agricultural fibers retained its shape but increased in weight by
Table 3 Water resistance of fiber-reinforced panels containing polyglucaramides
Soluble matter lost Polyglucaramide
State of panels after immersion Increase in weight
a
Poly octamethylene
D
-glucaramide nd
nd disintegrated
46 a 17
slight deformation 228 a
33 ab 183 ab
retained shape 33
50 172 ab
24 ac retained shape
6 d retained shape
130 c 67
Poly decamethylene
D
-glucaramide nd
nd disintegrated
17 45 a
184 a very slight deformation
34 b 171 a
retained shape 33
170 a 50
17 c retained shape
173 a 67
1 d retained shape
a
Within columns, means followed by the same letter do not differ significantly at a 95 confidence interval.
nearly 560 after immersion and lost 3.4 of its soluble
matter. Samples
containing only
polyvinyl alcohol
and a
-cellulose but
no polyglucaramide also completely disintegrated
during the immersion. For panels containing polyoctamethylene
D
- glucaramide, the increase in weight after immer-
sion and the amount of soluble matter lost during immersion
both decreased
with increasing
amounts of polyoctamethylene
D
-glucaramide Table 3. Linear regression analysis of the data
for weight increase gave an R
2
value of 0.955 while for soluble matter lost R
2
was 0.980. For panels
containing polydecamethylene
D
-glu- caramide, there was no significant change in
weight increase after immersion Table 3; R
2
= 0.474. However, the amount of soluble matter
lost decreased significantly so that there was virtu- ally no loss at the highest concentration of
polydecamethylene
D
-glucaramide R
2
= 0.995.
It was also observed that panels containing the polyglucaramides retained their shape during
immersion in contrast to the control samples which disintegrated during immersion.
These results show that the water resistance of fiber-reinforced pressed panels can be greatly im-
proved by including polyglucaramides in the formulation. In addition to improved water resis-
tance, inclusion of the polyglucaramides main- tained the structural integrity of the panels during
immersion in water. As the amount of polyglu- caramide in the panel increased, both the in-
crease in weight and the amount of soluble matter lost decreased substantially.
4. Conclusions
