Irving, 1995; Glenn et al., 1996, but they do not have good water resistance. Therefore, a water-re-
sistant coating must be applied to the starch- based product in order to impart water resistivity
to it. The purpose of the present study was to incorporate a water-insoluble polymer derived
from renewable resources in the formulation of starch-based plastic products in order to avoid the
need for a coating.
Polyglucaramides or hydroxylated nylons are one class of water-insoluble polymer derived from
renewable resources. These polymers are struc- turally analogous to nylons in that they are com-
posed of a diacid component and a diamine component. With polyglucaramides, the diacid
component is glucaric acid, a six-carbon diacid with hydroxyl groups at positions 2, 3, 4 and 5,
hence the term hydroxylated nylon. Glucaric acid is a product of the oxidation of glucose. The
chemistry of polyglucaramides was developed by Kiely and coworkers beginning in the late 1980s
Kiely and Lin, 1989; Kiely and Chen, 1994; Kiely et al., 1994; Chen and Kiely, 1996. The synthesis
of polyglucaramides involves a reaction se- quence based on unprotected esterified
D
-glucaric acid by simple condensation reactions. This sys-
tem is efficient and allows for a great deal of versatility in polymer composition because of the
large variety of diamines that can be used.
The first step in the production of polyglu- caramides is the hydrolysis of starch by either
chemical i.e. acid or enzymatic methods or a combined approach to glucose see Fig. 1. In the
second step, the glucose is oxidized to form glu- caric acid. Following a direct esterification of
glucaric acid, it can be reacted with a multifunc- tional amine, usually a diamine, to form the
polyglucaramide see Fig. 1. The polymeriza- tion reaction occurs at room temperature and no
specialized reaction conditions, such as an inert atmosphere, are needed. The polymer is isolated
by filtration.
In this
study, semicrystalline
polyglu- caramides were prepared and were processed
with various agricultural fibers to form composite panels.
2. Materials and methods
2
.
1
. Synthesis of
D
-glucaric acid
D
-glucaric acid was prepared according to a method modified from those of Mehltretter 1963
and Kiely et al. 1997.
D
-glucose 25.0 g; Sigma, St. Louis, MO and 26.4 ml of concentrated
HNO
3
Trace Metal Grade; 70 ww; Fisher, Pittsburgh, PA were placed in a 500 ml round
bottom flask. Bubbling N
2
gas was delivered to the mixture by way of a 10 ml pipette. The
temperature of the stirred mixture was raised to 45°C. After the glucose dissolved, the flask was
transferred to an ice bath and a few crystals of NaNO
2
Mallinckrodt, Paris, KY were added to initiate the oxidation. The temperature of the
mixture immediately began to increase and a large volume of brown gas was produced. The mixture
temperature was controlled with N
2
bubbling so that it did not exceed 60°C. After the temperature
decreased to approximately 40°C, the flask was transferred to a 45°C water bath for approxi-
mately 4 h and the N
2
bubbling was continued. After the production of brown gas subsided, an
additional 8.9 ml of concentrated HNO
3
was added and the flask was heated as before, at 45°C
with N
2
, for an additional 4 h. At this point, the oxidation was deemed complete. The mixture was
transferred to a 400 ml beaker in an ice bath and the pH was adjusted to 9.0 with 8 M KOH
Baker, Phillipsburg, NJ. Following cooling to room temperature, the solution was diluted with
distilled water and passed through a column 4 × 40 cm containing an ion retardation resin Bio-
Rad AG
®
11 A8; Bio – Rad, Hercules, CA. Fractions of approximately 200 ml were collected
from the column. The fractions of the product were then combined together and concentrated by
rotary evaporation to produce a viscous syrup. The syrup was transferred to a 400 ml beaker in
an ice bath and the pH was adjusted to between 3.5 and 4.0 with concentrated HNO
3
or until the monopotassium glucaric acid began to precipitate.
The monopotassium glucaric acid was then filtered, washed with cold ethanol, and dried in
vacuo at 65°C 55 yield. This reaction was also scaled proportionally for 300 g
D
-glucose 79 yield.
2
.
2
. Synthesis of poly glucaramides
A series of ten diamine compounds were used to synthesize the polyglucaramides in this study.
In all cases, the diamine was added to the es- terified glucaric acid as a 1.14 M methanol solu-
tion. The diamines Aldrich used are listed with the masses used of each in parentheses: 1,4-di-
aminobutane 1.78 g, 1,6-diaminohexane 2.35 g, 1,8-diaminooctane 2.91 g, 1,10-diaminodecane
3.48 g, 1,12-diaminododecane 4.05 g, 2-methyl- 1,5-pentanediamine 2.35 g, 1,3-diaminopentane
2.06 g, 4,9-dioxa-1,12-dodecanediamine 4.13 g, 4,7,10-trioxa-1,13-tridecanediamine 4.45 g, and
m-xylylenediamine 2.75 g. Polyglucaramides were all synthesized by a
direct esterification method adapted from Kiely et al. 1994. Acetyl chloride 3.0 ml; Aldrich, Mil-
waukee, WI was added dropwise with stirring to 25 ml of methanol HPLC grade; Fisher in a 250
ml round bottom flask cooled in an ice bath. Then, 5 g of monopotassium glucaric acid 20.1
mmol was added to the mixture. The round bottom flask was transferred to an oil bath and
the mixture was refluxed for 3 h. The mixture was cooled to room temperature and filtered to re-
Fig. 1. Formation and polymerization of glucaric acid
Table 1 Properties of synthesized polyglucaramides
Sample Yield
mp °C Crystal
M
n
NMR M
n
GPC M
w
GPC M
w
M
n
GPC polytetramethylene
60 195
– –
– –
–
D
-glucaramide 54
211 44
polyhexamethylene 882
426 529
1.2
D
-glucaramide polyoctamethylene
53 209
45 1034
380 506
1.3
D
-glucaramide 60
212 45
polydecamethylene 952
299 335
1.1
D
-glucaramide 66
213 41
polydodecamethylene 440
286 323
1.1
D
-glucaramide 74
211 45
polym-xylylene 3565
558 899
1.6
D
-glucaramide 2.2
45 211
41 poly4,9-dioxadode-
2254 638
1384 camethylene
D
-glucaramide 2.1
14 213
poly4,7,10-trioxatride- 48
3694 542
1123 camethylene
D
-glucaramide 37
– –
– –
– poly4-methylpen-
– tamethylene
D
-glucaramide 37
– –
– –
– –
poly1-ethyltrimethylene
D
-glucaramide
move KCl. The filtrate was concentrated by ro- tary evaporation at 65°C to a viscous syrup. The
syrup was then dissolved in 20 ml of methanol. Triethylamine Aldrich was added until the pH
was between 8.5 and 9.0. A methanol solution of the diamine 20.2 mmol was added and the entire
mixture stirred at room temperature for 3 – 4 h. The polymer typically began to precipitate within
10 – 20 min. After 3 – 4 h, the reaction mixture was filtered to isolate the polymer. The polymer was
washed three times with 10 ml methanol and three times with 10 ml acetone. The polyglucaramide
was dried in vacuo at 65°C for 12 h. Melting points
determined by
Differential Scanning
Calorimetry DSC, molecular weights deter- mined by Nuclear Magnetic Resonance NMR
spectroscopy and Gel Permeation Chromatogra- phyGPC, and crystallinity determined from the
X-ray powder patterns of the polymers are listed in Table 1.
The structures of the polyglucaramides were confirmed with NMR spectroscopy. Individual
results for the polymers are: Polyhexamethylene
D
-glucaramide:
1
H NMR DMSO d 3.98 d, 1H, H-2, 3.88 broad s, 1H, H-3, 3.69 dd, 1H, H-4,
3.93 dd, 1H, H-5, 3.07 broad d, 4H, H-1 and H-6, 1.40 broad s, 4H, H-2 and H-5, 1.25
broad s, 4H, H-3 and H-4. Polyoctamethylene
D
-glucaramide:
1
H NMR DMSO d 3.98 d, 1H, H-2, 3.87 t, 1H, H-3, 3.68 dd, 1H, H-4, 3.93
dd, 1H, H-5, 3.07 broad d, 4H, H-1 and H-8, 1.40 broad s, 4H, H-2 and H-7, 1.24 s, 8H,
H-3, H-4, H-5 and H-6. Polydecamethylene
D
-glucaramide:
1
H NMR DMSO d 3.97 d, 1H, H-2, 3.86 broad s, 1H, H-3, 3.68 dd, 1H, H-4,
3.92 broad d, 1H, H- 5, 3.07 m, 4H, H-1 and H-10, 1.40 broad s, 4H, H-2 and H-9, 1.24 s,
12H, H-3, H-4, H-5, H-6, H-7 and H-8. Poly- dodecamethylene
D
-glucaramide:
1
H NMR
DMSO d 3.97 d, 1H, H-2, 3.86 t, 1H, H-3, 3.68 dd, 1H, H-4, 3.92 d, 1H, H-5, 3.07 m,
4H, H-1 and H-12, 1.40 broad s, 4H, H-2 and H-11, 1.24 s, 16H, H-3, H-4, H-5, H-6, H-7,
H-8, H-9 and H-10. Polym-xylylene
D
-glu-
caramide:
1
H NMR DMSO d 4.12 d, 1H, H-2, 3.92 s, 1H, H-3, 3.80 dd, 1H, H-4, 3.99
d, 1H, H-5, 7.30 s, 1H, Ar-H, 7.21 d, 2H, Ar-H, 7.16 s, 1H, Ar-H, 4.30 dd, 4H, CH
2
-Ar. Poly4,9-dioxadodecamethylene
D
-glucaramide:
1
H NMR DMSO d 3.98 d, 1H, H-2, 3.87 t, 1H, H-3, 3.69 dd, 1H, H-4, 3.92 d, 1H, H-5,
3.36 d, 8H, H-3, H-5, H-8 and H-10, 3.14 d, 4H, H-1 and H-12, 1.65 t, 4H, H-2 and H-11,
1.52 s, 4H, H-6 and H-7. Poly4,7,10-trioxa- tridecamethylene
D
-glucaramide:
1
H NMR
DMSO d 3.99 d, 1H, H-2, 3.88 t, 1H, H-3, 3.70 dd, 1H, H-4, 3.92 d, 1H, H-5, 3.51 dd,
8H, H-5, H-6, H-8 and H-9, 3.41 t, 4H, H-3 and H-11, 3.14 d, 4H, H-1 and H-13, 1.65 t,
4H, H-2 and H-12.
2
.
3
. General analytical methods Nuclear magnetic resonance NMR spectra of
the polyglucaramides were recorded at 298 K from samples in dimethyl sulfoxide DMSO with
tetramethylsilane TMS as an internal standard on a Bruker ARX400 Billerica, MA spectrome-
ter operating at 400.14 MHZ for
1
H and 100.62 MHZ for
13
C. Single pulse experiments were run for both nuclei. A 30° pulse at a 2.3 s repetition
rate was used for the carbon spectra, and a 90° pulse at a 7 – 8 s repetition rate was used for the
proton spectra. The structures of the polymer products determined by NMR spectroscopy were
in agreement with previously published references Kiely et al., 1994; Chen and Kiely, 1996. NMR
was also used to estimate the molecular weight of the polymers obtained. Representative proton
spectra are shown for polyhexamethylene
D
-glu- caramide and poly4,9-dioxadodecamethylene
D
-glucaramide in Fig. 3 and Fig. 4, respectively. Differential scanning calorimetry DSC profi-
les of the polymers were measured using a TA Instruments DSC 2910 modulated DSC New
Castle, DE. In modulated DSC a sinusoidal os- cillation is overlaid on the linear heating ramp to
yield a heating profile in which the average sample temperature increases with time, but not in a
linear fashion. The effects of a more complex heating profile are as if multiple experiments were
determined simultaneously on the same sample; one at a linear heating rate and one at an instan-
Fig. 2. X-ray powder patterns of synthesized polyglucaramides
Fig. 3.
1
H NMR Spectrum of polyhexamethylene
D
-glucaramide
Fig. 4.
1
H NMR Spectrum of poly4,9-dioxadodecamethylene
D
-glucaramide
taneous heating rate. The DSC profiles were run from room temperature to 300°C at a heating rate
of 5°Cmin. All DSC scans were featureless from room temperature to the melting points near
210°C.
X-ray powder patterns Fig. 2 were measured on a Philips X’Pert diffractometer Mahwah, NJ.
Sample scans were run in continuous mode from 4.0 to 34.0° at a scan speed of 0.02°s. A fixed 15°
primary mask was used along with a fixed 0.5° divergence slit. Crystallinity was determined by an
integration method where the percent crystallinity was taken as the area of the diffractogram due to
the crystalline content divided by the total area under the diffractogram both crystalline and
amorphous content.
Molecular weights of the synthesized polymers were determined using NMR and gel permeation
chromatography GPC. For NMR analysis the method of Shit and Maiti 1986 was used
wherein the molecular weight is determined based on the integration of the
1
H NMR spectrum. The integration for the end group protons of the poly-
mer is compared to the integration for a known set of protons in the backbone of the polymer in
order to calculate the average degree of polymer- ization, and thus M
n
. For GPC analysis, aliquots were dissolved in DMSO High Purity; Burdick
and Jackson, Muskegon, MI and injected onto a column bank Waters Associates Styragel HT6E,
HT6E, HT2, maintained at 60°C, and eluted with DMSO at a flow rate of 0.3 mlmin. Detection
was by refractive index Water Associates Model 410, Milford, MA at 50°C. Molecular weights
were calculated by interpolation to a calibration curve generated using a polysaccharide calibration
kit Polymer Laboratories, part number 2090- 0100, Amherst, MA, under identical chromato-
graphic
conditions. The
molecular weights
obtained by GPC were lower than those estimated from NMR see Table 1. In general, the samples
showed narrow polydispersities of between 1.1 and 2.2.
2
.
4
. Formation of pressed test panels Fiber reinforced test panels were fabricated us-
ing polyglucaramides as a water-insoluble binder with polyvinyl alcohol, which is a water soluble
polymer chosen to highlight the water resistance of polyglucaramides and cellulose fiber. The
panels 125 × 32 × 2 mm were prepared by press- ing the components in a mold on a laboratory
Carver Press Model C; Carver Inc., Wabash, IN. Panels contained 0 – 66 polyvinyl alcohol
Airvol 203S; Air Products, Allentown, PA, 0 – 66
polyglucaramide and
33 a
-cellulose Sigma, which had previously been ground in a
Wiley mill c 20 mesh. The various mixtures were dry-mixed by passing them through a Wiley
mill c 10 mesh prior to introduction into the mold. The panels were pressed at 210°C and
34474 kPa 5000 psi for 1 min. The mold was removed from the press and allowed to cool for 2
min before removing the panel. All of the polyglucaramide fabricated panels were tested
for quality including visual appearance, presence of voids and uniformity. The best candidates were
selected for further testing. These were the poly- octamethylene
D
-glucaramide and
polyde- camethylene
D
-glucaramide panels. Six panels of each of the composition listed in Table 2 were
prepared and tested for mechanical properties and water absorption.
2
.
5
. Mechanical testing of pressed test panels Panels were tested mechanically in an Instron
universal testing machine Model 4500; Canton, MA using Series IX Automated Materials Test-
ing System version 7.50. The panels were tested using a standard plastics tensile test derived from
ASTM method D638M-91a Annual Book of ASTM Standards, 1992. The crosshead speed
was 25.0 mmmin with a 1.0 kN load. The tensile strength and Young’s modulus were calculated by
the computer software. The tensile strength was calculated as the maximum tensile stress reached
by the sample during the tensile test. Young’s modulus was taken as the initial slope of the
stress – strain curve.
2
.
6
. Water absorption test The water absorption test to determine the
water resistance of the pressed panels was based on ASTM D 570-95 Annual Book of ASTM
Standards, 1996 entitled Standard Test Method for Water Absorption of Plastics. The specimens
were cut to size 36 × 32 mm using a utility knife. Each specimen was weighed to the nearest 0.0001
g and its dimensions width, length and thickness were measured. The specimens were then condi-
tioned for 16 h at 50°C. They were weighed conditioned weight and immersed in distilled
water for 24 h at room temperature 23 9 2°C. After 24 h, the specimens were removed from the
water, the surface water wiped off with a dry cloth and weighed wet weight. The physical state
of specimens after immersion was also noted. After weighing, the specimens were reconditioned
by drying for 24 h at 50°C, and reweighed recon- ditioned weight. This test provides two useful
values. The first is the percentage increase in weight during immersion:
Increase in weight, = [wet weight − conditioned weight
conditioned weight] × 100 The second is the percent soluble matter lost
during immersion:
Table 2 Mechanical properties of fiber-reinforced panels containing
polyglucaramides Tensile strength
Polyglucaramide Young’s
MPa
a
modulus MPa Poly
octamethylene
D
-glucaramide 94 a
0.346 ab 0.561 bc
17 180 b
33 0.894 c
129 c 50
0.996 c 183 b
1.30 cd 67
203 b Poly
decamethylene
D
-glucaramide 94 a
0.346 a 1.02 b
17 200 b
0.823 b 33
151 bc 50
0.915 b 137 cd
0.573 bc 67
129 cd
a
Within columns, means followed by the same letter do not differ significantly at a 95 confidence interval.
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
