New broom fiber (Spartium junceum L.) derivatives: Preparation and characterization

Article abstract of DOI:10.1021/jf071711k

In the past decade interest in biopolymers has increased. Attempts were made to prepare new composite systems from biopolymers by binding different synthetic polymers to a biopolymer backbone. This paper reports the synthesis and characterization of deriv

Full text of DOI:10.1021/jf071711k

J. Agric. Food Chem. 2007, 55, 9489–9495 9489
New Broom Fiber (Spartium junceum L.) Derivatives:
Preparation and Characterization
,
†
†
†
ROBERTA CASSANO,* SONIA TROMBINO, ERMELINDA BLOISE,
†
†
§
RITA MUZZALUPO, FRANCESCA IEMMA, GIUSEPPE CHIDICHIMO, AND
†
NEVIO PICCI
Departments of Pharmaceutical Sciences and Chemistry, University of Calabria, Rende (CS), Italy
In the past decade interest in biopolymers has increased. Attempts were made to prepare new
composite systems from biopolymers by binding different synthetic polymers to a biopolymer backbone.
This paper reports the synthesis and characterization of derivatized broom fibers to prepare composites
with either degradability or fireproofing properties. Synthetic strategies are described for the introduction
of polymerizable functional groups or fluorine atoms on the glucose of cellulose chains of broom.
The fibers containing polymerizable groups were copolymerized with dimethylacrylamide and styrene
and, after that, investigated by optical polarizing microscopy (OPM) and scanning electron microscopy
analysis (SEM). The materials containing fluorine were submitted to thermogravimetric analysis (TGA)
and differential scanning calorimetry (DSC) for the purpose of verifying the fireproofing. Such
derivatized biomaterials could be successfully used for applications in agriculture and in the packaging
area.
KEYWORDS: Broom fibers; functionalization; fluorine; agriculture; packaging; polymer
INTRODUCTION
such as their poor compatibility with a hydrophobic polymer
matrix, the high affinity of natural fibers toward water, and their
relatively poor thermal stability. This leads to the formation of
weak interfaces that result in poor mechanical properties of the
composites.
Over the past decade, polymer composites reinforced with
natural fibers have received ever-increasing attention, from both
academic and industry points of view. The main advantages
that they have are low cost and high specific mechanical
properties that allow their usage as a good, renewable alterna-
tives to the most common synthetic reinforcement, such as glass
fibers, which are not biodegradable (1–3). There is a wide variety
of different natural fibers applicable as reinforcement or fillers.
Cotton, jute, and flax are the vegetable fibers most commonly
used to reinforce polymers such as polystyrene (4, 5), polyesters
For such reason the idea to link halogenated or polymerizable
molecules to broom fibers by covalent bond (Figure 1) to
produce poorly flammable materials and to improve fiber
strength and fiber/matrix adhesion in fiber composites was
conceived (11). These systems could be applied in agriculture
and in the packaging area. In this paper, we report the synthesis
and characterization of broom fiber derivatives obtained by
esterification with molecules containing fire retardant or poly-
merizable groups. Trifluoroacetic acid and heptafluorobutyric
acid were used as efficient flame retardants in substitution of
ozone-depleting and toxic substances containing chlorine and
bromine (12). To obtain renewable plastic fibers, they were
initially reacted with acryloyl chloride, 4-vinylbenzyl chloride,
and 4-vinylbenzoyl chloride. Oxidized broom fibers were suc-
cessfully used to prepare an amide-linked polymerizable con-
jugate with 4-aminomethyl styrene chlorohydrate. The obtained
materials were characterized by Fourier transform infrared (FT-
IR) spectroscopy; the degree of substitution (DS) of ester, ether,
and amide derivatives was determined by titration. Moreover,
the fireproofing of materials containing fluorine was evaluated
by thermogravimetric analysis (TGA) and differential scanning
calorimetric (DSC) measurement. The broom fibers derivatized
with polymerizables groups were copolymerized with dimethy-
lacrylamide and styrene, both in equimolecular amounts or with
(
6), polyolefins (7, 8), and epoxy resins (9, 10) due to their
availability and properties. Broom is a further important fiber
with numerous advantages, abundantly available, and biode-
gradable; because it is made of cellulose, on combustion, broom
fibers do not generate toxic gases and are able to produce
materials by combination with plastic mixtures. These fibers,
known as vermenes, show extraordinary traction resistance and
flexibility. Broom fiber and generally vegetable fiber composites
provide improved specific or synergistic characteristics not
obtainable by any of the original components alone and can be
highly cost-effective materials for a number of applications such
as those for the food industry. Besides the advantages mentioned
above, the fiber composites possess also some disadvantages
*
Corresponding author (telephone +39 984493296; fax +39
9
84493163; e-mail roberta.cassano@unical.it).
†
Department of Pharmaceutical Sciences.
Department of Chemistry.
§
1
0.1021/jf071711k CCC: $37.00  2007 American Chemical Society
Published on Web 10/19/2007

9490 J. Agric. Food Chem., Vol. 55, No. 23, 2007
Cassano et al.
material was filtered off, washed with diethyl ether (300 mL), and dried
at room temperature for 20 h under vacuum. The crude product contains
traces of TFA and diethyl ether. These impurities can be removed by
heating the product to 150 °C for 40 min under vacuum (14). FT-IR
analysis confirmed ester linkage of trifluoroacetic derivative 2. Yield
)
1.4 g.
Synthesis of Heptafluorobutyrate Broom Fibers (3). This deriva-
tive was prepared according to the same procedure as in the previous
section employing 0.9 g of pretreated broom fibers, 20 mL of
Figure 1. Schematic illustration of fiber derivatization.
heptafluorobutyric acid (CF
tyric anhydride (CF CF CF
IR analysis confirmed ester linkage of heptafluorobutyric derivative 3.
Yield ) 0.49 g.
3
CF
CO)
2
CF
2
COOH), 10 mL of heptafluorobu-
the comonomers in large excess to obtain fibers covered from
one polymeric girdle. These latter, inserted as support fibers in
polymeric materials, would furnish strong interfaces and then
composites with a much greater resistance than those realized
with nontreated fibers. The unreacted, derivatized, and polym-
erized broom fibers were submitted to morphological analysis
using high-resolution optical and scanning electron microscopes.
3
2
2
2
O, and 200 mL of diethyl ether. FT-
Synthesis of Acrylate Broom Fibers (4). To a heterogeneous system
of 1.1 g of pretreated broom fibers in 50 mL of DMA and 3.3 g of
LiCl in a three-necked flask equipped with a stirrer was added under
inert atmosphere a mixture of 10 mL (0.124 mol) of dried pyridine
and 20 mL of DMA (15). Acryloyl chloride (5 mL, 0.061 mol) was
added within 30 min. The stirring was continued at room temperature.
Then the heterogeneous reaction mixture was initially left to stand
overnight and stirred for a further 6 h at 30 °C. After that, it was filtered
off, washed with 200 mL of methanol, suspended in 96% (w/w) ethanol,
and carefully dispersed. After filtration and washing with ethanol (four
times with approximately 25 mL of ethanol), the material was dried at
MATERIALS AND METHODS
Chemicals and Materials. Natural cellulose fibers from broom
(
Spartium junceum L.) were supplied by Prof. G. Salerno (Depart-
ment of Chemistry, University of Calabria, Italy). N,N-Dimethyl-
formamide (DMF), N,N-dimethylacetamide (DMA), lithium chloride
(
LiCl), dicyclohexylcarbodiimide (DCC), thionyl chloride (SOCl
pyridine (Py), sulfuric acid (H SO ), sodium hydroxide (NaOH),
acryloyl chloride (CH dCHCOCl), trifluoroacetic acid (CF COOH;
TFA), trifluoroacetic anhydride [(CF CO) O; TFAA], heptafluo-
robutyric acid (CF CF CF COOH), heptafluorobutyric anhydride
CF CF CF CO) O, 4-vinylbenzyl chloride (CH dCHC CH Cl),
2
),
50 °C under vacuum. FT-IR analysis confirmed ester linkage of acrylic
2
4
derivative 4. Yield ) 1.4 g.
Synthesis of Vinylbenzoate Broom Fibers (5). Thionyl chloride
2
3
3
2
(
14.6 mL) was added to 10.8 g (0.072 mol) of 4-vinylbenzoic acid,
3
2
2
and the mixture was stirred for 2 h at 40 °C. The residual SOCl content
was removed by distillation under vacuum, and after that, 6.2 g of
vinylbenzoyl chloride was collected at 81 °C/2 torr. The latter (5.8 g,
2
(
3
2
2
2
2
6
H
4
2
vinylbenzoic acid, dimethylacrylamide (DMAA), styrene, azobi-
s(isobutyronitrile) (AIBN), potassium phthalimide, hydrazine mono-
hydrate, hydrochloric acid, phosphoric acid, calcium acetate,
phenolphthalein, and sodium nitrite were supplied by Sigma
Chemical Co. (St. Louis, MO). Ethanol and diethyl ether were
obtained from Fluka Chemika-Biochemika (Buchs, Switzerland) and
Carlo Erba Reagents (Milan, Italy). Water, trifluoroacetic acid
0
.03 mol) was added, within 30 min, to a solution of pretreated broom
fibers (0.8 g) in 36 mL of DMA, 2.4 g of LiCl, and 7 mL of dry
pyridine. Then the heterogeneous system was left to stand overnight
and stirred for a further 6 h at 30 °C. After the addition of methanol
(200 mL), filtration, suspension in ethanol (150 mL), and final filtration,
the sample was dried at 50 °C under vacuum. FT-IR analysis confirmed
ester linkage of acrylic derivative 5. Yield ) 0.9 g.
(
3
CF COOH), and acetonitrile (ACN) were of HPLC grade and
obtained from Fluka Chemika-Biochemika.
Synthesis of Vinylbenzyl Ether Broom Fiber Derivative (6).
Pretreated broom fibers (1.1 g) were suspended in 50 mL of DMA and
3.3 g of LiCl. After the addition of 10 mL (0.124 mol) of dried pyridine
and 20 mL of DMA, 8.5 mL of 4-vinylbenzyl chloride (9.2 g, 0.060
mol) was added slowly during 10 min. The mixture was stirred for
70 h at 25 °C and for 6 h at 30 °C. After cooling at room temperature,
the resulting material was amended with methanol (200 mL), filtered
off, and washed many times with ethanol (200 mL). The product was
dried at 50 °C under vacuum. FT-IR analysis confirmed ether linkage
of derivative 6. Yield ) 0.8 g.
Measurements. FT-IR spectra were measured on a Jasco 4200
using KBr disks. UV–vis spectra were performed by a V-530 JASCO
spectrophotometer. HPLC analysis was performed with a Jasco BIP-I
pump and a Jasco UVDEC-100-V detector set at 247 nm. A C18
Supelcosil LC-18 material, 3 µm particle size, in a 4.6 × 150 mm
cartridge format (Supelco, Bellefonte, PA) column with linear
gradient 0% B–100% B in 10 min (A, 0.1% CF
.1% CF COOH in ACN, 1 mL/min) was employed. The measure-
ment of transition temperatures was carried out using DSC-
3 2
COOH in H O; B,
0
3
-
1
NETZSCH 200 by heating 0.8 mg of sample at 5 °C min , operated
under nitrogen. Scanning electron microscopy (SEM) photographs
of the materials before and after polymerization were obtained with
a JEOL JSMT 300 A; the surface of the samples was made
conductive by deposition of a gold layer on the samples in a vacuum
chamber. The polymerized materials were also studied with an
Olympus FV1000-IX81 polarizing optical microscope. Thermo-
gravimetric analysis of halogenated broom fibers was performed in
air using a Perkin-Elmer Pyris 1 TGA.
Synthesis of Oxidized Broom Fiber–Aminomethyl Styrene Con-
jugate (7). Appropriate amounts of oxidized broom fibers (0.8 g,
-3
equivalent to 2.3 mmol/g of COOH), DCC (1.6 g, 8 × 10 mol), and
-3
AMS (16) (1.2 g, 7 × 10 mol) were placed in 60 mL of DMF and
stirred at room temperature. The concentration of free AMS was
periodically monitored by HPLC. The reaction supernatant (250 µL)
was withdrawn, appropriately diluted with the HPLC mobile phase,
and then analyzed. The reaction was stopped when the amount of AMS
in the reaction medium no longer declined. The reaction mixture was
then filtered, and the material obtained was thoroughly washed with
methanol (150 mL) and dried at 50 °C in a vacuum desiccator. FT-IR
analysis confirmed ester linkage of amidic derivative 7. Yield ) 0.9 g
of pure product.
Fiber Chemical Modification. Broom fibers were pretreated to
obtain delignified materials (13). In particular, the broom fibers were
reacted with aqueous alkali (about 10% NaOH) for 10 min (under
reflux) and filtered to obtain the complete separation of fibrous
substances from the marrow. The delignified materials were washed,
until neutrality, with distilled water and then autoclaved with pressur-
izing air (40 bar of total pressure) for 3 h to 120 °C.
Pretreated broom fibers were subjected to the heterogeneous reactions
shown in Scheme (1 after drying overnight at 80 °C under reduced
pressure until a constant weight.
Determination of the Carboxyl Group Content of Cellulose
Samples by Methylene Blue Sorption. A weighted fiber sample was
suspended in 25 mL of aqueous methylene blue chloride solution (300
mg/L) and 25 mL of borate buffer of pH 8.5 for 1 h at 20 °C in a 100
mL flask and then filtered. Ten milliliters of the filtrate was transferred
to a 100 mL calibrated flask. Then 10 mL of 0.1 N HCl and
subsequently water, up to 100 mL, were added. Then the methylene
blue content of the liquid was determined photometrically, employing
Synthesis of Trifluoroacetate Broom Fibers (2). TFA (40 mL)
was added to 1.0 g of pretreated broom fibers, and the mixture was
kept for 20 min at room temperature. Then 20 mL of TFAA was added
and the mixture was stirred at room temperature for 4 h. The resulting

New Broom Fiber Derivatives
J. Agric. Food Chem., Vol. 55, No. 23, 2007 9491
Scheme 1. Various Routes to Regioselectively Functionalized Pretreated Broom Fiber Esters and Ether with Different Moieties
a calibration plot, and from the result the total amount of free,
nonsorbed, methylene blue is calculated. The carboxyl group content
of the sample is obtained according to
Determination of Vinylbenzyl and Aminomethyl Styrene Content
of Derivatives 6 and 7. The classical method to obtain information on
the vinyl group of 6 and 7 is the number iodine determinations (19).
(
blank titers - sample titer, mL)(0.01269)(100)
mmolof COOH/g of oven-dry sample ) [(7.5 - A) × 0.00313]/E
iodine no. )
sample wt (g)
(
1)
(
3)
where A is the total amount of free methylene blue (mg) and E is the
weight of oven-dry sample (g) (17, 18).
An iodine monochloride (Wij;s reagent) reagent is reacted with the
double bonds, and the excess reagent (as iodine) is titrated with sodium
thiosulfate solution. More exactly, 0.3 g of 6 was mixed with 20 mL
if Wij’s solution and 10 mL of carbon tetrachloride/glacial acetic acid
Quantitative Analysis of Ester Groups. A sample of 50 mg of
ester derivative was dispersed in 5 mL of 0.25 M ethanolic sodium
hydroxide solution under reflux for 17 h. The dosing in return of the
excess of soda was realized by titration with 0.1 N HCl (first equivalent
point). The moles of chloride acid used between the first and second
equivalence correspond to the moles of free esters. The degree of
substitution (DS) was determined by
3
:7. It is then left in the dark for 30 min. Next, 15 mL of 10% potassium
3
iodide solution and 10 cm of deionized water are added. This is then
titrated against 0.1 M sodium thiosulfate(VI) solution and five drops
of 1% starch paste solution. One milliliter of 0.1 M sodium thiosulfate
solution is equal to 0.01269 g of iodine. The difference between a
control titration and the titration with the fat present multiplied by this
factor gives the mass of iodine absorbed by the broom fiber derivatives
MMglucose unit
DS )
(2)
(
gsample/nfree ester
)
- MMfree ester - MMH O
(
)
2
6
and 7.
where nfree ester is equal to (V2° ep – V1° ep) × [HCl], MMglucose unit is the
Copolymerization of Broom Fibers. The grafting of derivative 4,
molecular mass of the glucose unit, gsample is the weight of the sample,
with structopendant unsaturated ester moieties, was carried out in DMF
employing AIBN as initiator and DMAA or styrene as comonomer
(20). The materials copolymerized with DMAA were washed first with
n
free ester is the moles of free ester, MMfree ester is the molecular mass of
free ester, and MMH2O is the molecular mass of water.

9492 J. Agric. Food Chem., Vol. 55, No. 23, 2007
Cassano et al.
Table 1. Experimental Conditions of the Copolymerization Reactions
washing solvents
derivative 4 (g) comonomer DMAA (g) comonomer styrene (g) initiator AIBN (g) solvent DMF (mL) H2O (mL) washing solvents n-hexane (mL) acetone (mL)
1
0
0
0
.0
0.46
9.62
0.01
0.30
0.01
0.22
25.0
25.0
25.0
25.0
3·20
3·300
3·20
.57
.50
.51
3·300
3·20
3·300
0.5
7.13
3·20
3·300
Table 2. Degree of Substitution Values of Compounds 2–5
water and after with acetone. On the contrary, those copolymerized
with styrene were washed initially with n-hexane and subsequently with
acetone. The experimental conditions of the copolymerization reactions
are reported in Table 1. Further studies to prepare copolymers of the
materials 5–7 are in progress.
compound
substitution degree
2
3
4
5
0.82
0.37
1.70
0.71
RESULTS
Synthesis of Broom Fiber Derivatives 2–7. Halogenated or
polymerizable materials (2–6) were realized from pretreated
broom fibers using trifluoroacetic and heptafluorobutyric acids
or acryloyl chloride, vinylbenzoyl chloride, 4-vinylbenzyl
chloride. Moreover, the conjugate 7 was prepared after initial
oxidation of broom fibers and subsequent reaction with ami-
nomethyl styrene chloridate. The formation of broom cellulose
esters of organic acids was conducted along the routes of
esterification of alcoholic hydroxy groups, well-known from
low molecular organic chemistry: the chloride of the organic
acid in question or the anhydride with the corresponding acid
was employed as the agent to obtain an appreciable degree
of esterification. Halogenated esters of broom cellulose (2,
cellulose compounds still containing a fairly large number of
free hydroxy groups. Thus, information on the extent of
reaction and on distribution of the substituents is of great
importance. The extent of reaction is usually characterized
by the DS, denoting the average number of hydroxy groups
modified per AGU, and thus covering the range from 0 to 3.
With regard to the DS values of samples 2–5, determined
by titration and calculated by eq 1, they were 0.82 and 0.37
for trifluoroacetate (2) and heptafluorobutyrate (3) esters,
respectively, 1.70 for acrylate derivative (4), and finally of
0.71 for vinylbenzoate derivative (5) (Table 2).
Vinylbenzyl and Aminomethyl Styrene Content of Deriva-
tives 6 and 7. Samples 6 and 7 were independently reacted
with an excess of iodine monochloride solution (Wij’s reagent)
under controlled conditions. Halogens add quantitatively to the
vinyl group. Unreacted halogens were determined by titration
with thiosulfate. The iodine number, defined as the grams of
halogen, expressed as iodine, was 17 (corresponding to 0.65
mmol/g) for derivative 6 and 26 (equivalent to 0.98 mmol/g)
for derivative 7.
3
) with substituted monocarboxylic aliphatic acids were
prepared by reaction with a mixture of CF3COOH and
CF3CO)2O or CF3CF2CF2COOH and (CF3CF2CF2CO)2O.
(
Partial recovery of derivative 3 was ascribed to the remark-
able fragmentation of fibers after treatment with
CF3CF2CF2COOH and (CF3CF2CF2CO)2O. Acrylate and
vinylbenzoate esters (4, 5) were prepared with acryloyl- or
vinylbenzoyl chloride as the agent in the presence of pyrydine
in DMA/LiCl as the medium (21). Cellulose etherification was
performed with the broom fibers suspended in an aprotic system
such as DMA/LiCl to obtain 6. The synthesis pathway consists
in the reaction of fibers with 4-vinylbenzyl chloride in the
presence of pyridine as base (22). Finally, the oxidized broom
fiber–aminomethyl styrene conjugate 7 was prepared through
reaction of 6-carboxy fiber derivatives with 4-aminomethylsty-
rene chloridate using N,N′-dicyclohexylcarbodiimide as a
condensation agent and N,N-dimethylformamide as solvent. The
FT-IR Investigations. FT-IR spectroscopy was used to obtain
qualitative information about the broom fibers after derivatiza-
tion. The FT-IR spectra of unreacted broom fibers (1) and
derivatives 2–7 are compared in Figure 2. As reported, the band
at 1644 cm- (spectrum a) typical of unreacted broom fibers is
visible in the spectra of all derivatives. Additionally, spectrum
b of 2 shows the characteristic peak of carboxylic group of ester
at 1786 cm- . The spectrum of derivative 3, not shown, is
1
1
-
1
analogous to spectrum b. The peaks at 1729 and 1722 cm in
spectra d and f are due to CdO stretching vibration belonging
to the carboxylic groups of the esters 4 and 5. Note the stretching
6-carboxy broom fiber derivative was synthesized in accordance
with a procedure found in the literature (23), and the determi-
nation of carboxyl group content was realized by methylene
blue sorption (17). Its FT-IR spectra showed considerable
changes in comparison with the spectra of starting fibers and
an oxidized sample. The formation of all broom fiber derivatives
was confirmed by FT-IR spectroscopy. Their yields are 1.4 g
for trifluoroacetate broom fibers, 0.49 g for heptafluorobutyric
derivative, 1.4 g for acrylic ester, 0.9 g for vinylbenzoate broom
fibers, 0.8 g for vinylbenzyl ether broom fiber derivative, and
-
1
vibration of vinyl group (CdC) with the ether 6 at 1655 cm
in spectrum c. The peak at about 1732 cm- in spectrum e is
1
due to CdO (amide) stretching vibration of the amide 7. In
-
1
spectra e, f, and c the peaks between 3000 and 3100 cm are
assigned to C–H (aromatic) stretching vibration due to the
phenyl group of compounds 5–7.
High-Resolution Optical Microscopy and Scanning Elec-
tron Microscopy (SEM). The surface roughness characteriza-
tion was initially effected through investigation with high-
resolution optical microscope (Figure 3). Morphological analysis
of the fiber was also carried out using SEM, which is the most
widely used of the surface analytical techniques. SEM represents
an invaluable tool for studying surface topography and failure
analysis. The technique, which enables qualitative three-
dimensional (3-D) imaging of surface features, clearly illustrated,
as did the optical microscopy, that the untreated broom fiber
0
.9 g for oxidized broom fiber–aminomethyl styrene
conjugate.
Carboxylic Group Content of Broom Fiber Derivatives
2
–5 (DS). Complete or partial esterification of the hydroxy
groups is among the principal reaction routes to the cellulose
derivatives carrying covalently bound substituents. A complete
functionalization of all the hydroxy groups of cellulose is
more an exception than a rule, and most of the products are

New Broom Fiber Derivatives
J. Agric. Food Chem., Vol. 55, No. 23, 2007 9493
Figure 3. Optical micrographs of acrylated broom fibers copolymerized
with (a) a stoichiometric amount of DMAA and (b) an excess of DMAA.
material that maintains unchanged its fibrous nature but show
that it is covered by a polymeric layer to the same fiber. The
material functionalized with styrenic groups, copolymerized with
an equimolecular amount or excess of styrene, furnished fibrous
materials covered with a varying thickness layer of styrenic
polymer. The thickness of the polymeric layer is obviously a
function of the excess of comonomer used. Photomicrographs
of the surface of copolymerized fibers show what has been, until
now, suggested.
TGA. In a TGA mass loss versus increasing temperature of
a sample is recorded. The TGA was performed on heating from
3
0 to 600 °C 5 mg samples at 10 °C/min under oxygen flow
(30 mL/min). Experiments were repeated twice. These operating
conditions allowed us to study the thermo-oxidative degradation
of broom fibers modified with fireproofing compounds such as
trifluoroacetic and heptafluorobutyric acids. Figure 5 reports
the weight loss curves (top) and the corresponding weight loss
rates (bottom). Thermo-oxidative degradation of underivatized
fibers takes place in two steps. The first step of volatilization
(
between 225 and 400 °C with a maximum rate of decomposi-
tion υmax dec at 357 °C) left a carbonaceous residue of about 40
wt % of the initial mass, whereas in the second step (between
4
10 and 520, υmax dec at 474 °C) the residue is fully volatilized.
The poly fluoro acid treatment modifies the thermo-oxidative
behavior of broom fibers with respect to those not derivatized.
Similarly to what was observed for the neat fibers, heptafluo-
robutyric acid derivatized fiber 3 thermo-oxidative weight loss
takes place in two well-separated steps; however, the first step
of weight loss is shifted to lower temperature (from υmax dec )
3
57 °C to υmax dec ) 319 °C), whereas the second step takes
place abruptly, as evidenced by the sharpened weight loss rate
curve (Figure 5, bottom). The trifluoroacetic acid derivatized
fiber (2) has three steps of weight loss: the first two, partially
overlapped, from 225 to 370 °C with υmax dec at 286 and 306
°
C, the third one from 380 to 420 °C with υmax dec at 405 °C.
The release of halogen derivates, which is a fundamental step
of the flame-retardant mechanism of halides (24), may explain
the reduced thermal stability of derivatized fibers, evidenced
by the shift to lower temperature of the first weight loss steps.
The last weight loss steps, at 474 °C for 3 and at 405 °C for 2,
respectively, may be due to a rapid collapse of a protective
Figure 2. FT-IR spectra of broom fibers: unreacted (1); trifluoroacetate
(2); vinylbenzyl ether (6); acrylated (4); oxidized broom fiber–aminomethyl
styrene conjugate (7) vinylbenzoate (5).
(carbonaceous) layer formed during the earlier thermo-oxidative
degradation steps of the chemically modified fibers, followed
by an abruptly oxidation of the organic residue. To fully
understand the chemical degradation mechanism that led to the
observed thermo-oxidative behaviors, a more focused study is
needed.
surface (Figure 4a) was not more homogeneous than that
exhibited by materials copolymerized with a stoichiometric
amount of DMAA (Figure 4b) and copolymerized with an
excess of DMAA (Figure 4c). All derivatives are shown to be
fibrous and to have a smoother surface compared with that of
untreated fibers. The broom fibers containing acrylic groups
furnished, after copolymerization with dimethylacrylamide, a
DISCUSSION
Broom fiber derivatives with a variety of DS values were
successfully prepared by introducing polymerizable or polyha-

9494 J. Agric. Food Chem., Vol. 55, No. 23, 2007
Cassano et al.
Figure 4. Photomicrographs of broom fibres: (a) unreacted; (b) copolymerized with a stoichiometric amount of DMAA; (c) copolymerized with an excess
of DMAA.
Figure 6. Schematic illustration of polymerized halogenated fibers.
resistance to those realized with nontreated fibers. In the future,
derivatives containing fluorine atoms will be submitted to
treatment with compounds containing polymerizable groups to
obtain halogenated, poorly flammable, polymerizable materials
(
Figure 6). These materials, entirely obtained by renewable
sources, could be used in agriculture, in the realization of
cordage or for packings of natural products, or to replace
aluminum-based containers (25, 26) used in food packaging.
In fact, the National Institute of Nutrition (NIN), which is part
of the Indian Council of Medical Research, has concluded that
the intake of aluminum compounds from many sources is on
the rise and producing detrimental effects on human health.
Particularly, the aluminum may contribute significantly to the
development of Alzheimer’s disease and other nervous disorders
Figure 5. Thermogravimetry (a) and derivative (b) curves of broom fibers
and of fibers functionalized with trifluoroacetic and heptafluorobutyric acids.
logenated residues in pretreated material. The formation of all
broom fiber derivatives was confirmed by FT-IR spectroscopy.
Fluorinated material thermal stability was evaluated by TGA.
The results suggested that the presence of the fluorine atoms
changes the thermal decomposition behavior of broom fibers.
The decreased ignition of broom fibers modified with TFA in
comparison with heptafluorobutyrate derivative is mostly at-
tributed to the different DS. Relative to the broom fibers
derivatized with polymerizable groups, the choice to use
acrylamidic or styrenic monomers for their covering has been
dictated by the necessity to have on the surface a hydrophilic
or lipophilic polymeric layer, covalently linked to the fiber. This
should allow the fibers so modified to be used as filler in
composite polymeric material that should present a much greater
(
27).
ACKNOWLEDGMENT
We thank Prof. G. Camino and Dr. A. Castrovinci (Center
of Culture for the Engineering of the Plastic Materials, Turin
Polytechnic-Center of Alexandria) for the thermogravimetric
analysis.

New Broom Fiber Derivatives
J. Agric. Food Chem., Vol. 55, No. 23, 2007 9495
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