Keywords
:
Boehmeria ni6ea; Spartium junceum; Spanish Broom; Ramie; Fibre; Mechanical properties; Interface strength; Composite materials
1. Introduction
Application of vegetable products in various branches of industry will benefit from their intrin-
sic biocompatibility and biodegradability. Indus- tries all over the European Community are
looking for raw material for replacing artificial fibres in composite materials CMs to alleviate
problems related with CMs disposal at the end of the technical life. Vegetables fibres could be a
viable alternative to man-made fibres especially asbestos and glass fibres at least in applications
in which the overall performance, evaluated in term of life cycle analysis, has to take into ac-
count the final disposal. A number of suitable plant fibres can be successfully grown in Italy,
including Ramie Boehmeria ni6ea L. Gaud., a member of the Urticaceae, and Spanish Broom
Spartium junceum L. for which promising agro- nomic results have been obtained Oggiano et al.,
1997.
Ramie is a perennial plant native to China, Japan, and the Malay Peninsula, where it has
been used as a textile fibre for centuries due to its excellent fibre Kirby, 1963; Wood and Angus,
1974; Batra and Bell, 1975. The fibres, obtained from the outer part of the stem, are the longest
and one of the strongest fine textile fibres Dempsey, 1975; Jarman et al., 1978. Other ad-
vantages of this fibre is the resistance to bacteria, mildew, and insect attack. Its strength slightly
increases when wet Fontanelli, 1998.
Spartium junceum belonging to the Legumi- nosae family is a perennial shrub, wide-spread
throughout the Mediterranean area Munz and Keck, 1973; Pignatti, 1982 where it naturally
occurs in hilly soils, contributing to lower erosion and risks of nutrient leaching. This plant is some-
what adapted to alkaline and salty soils. The name Spartium is from the Greek word denoting
‘cardage’, in allusion to the use of the plant. By macerating the twigs a good fibre was obtained,
which was made into thread and cords and a coarse sort of cloth. It was cultivated on a large
scale in southern Italy around the thirties; but later it fell out of favour. Recently there has been
a revival of interest in Spanish Broom as a possi- ble source of raw materials to be used in CMs for
automobile applications.
The agronomic characteristics of Ramie and Spanish Broom were investigated for seven years
in the pedoclimatic conditions of Central Italy. In order to evaluate the feasibility to use Ramie and
Spanish Broom fibres in composite materials, the morphology and chemical composition together
with physical and mechanical properties of these fibres were also examined.
2. Materials and methods
2
.
1
. Agronomic aspects A 7-year field trial was set up at the Depart-
ment of Agronomy of the University of Pisa about 43°N; 10°E; 3 m elevation on a deep silt
loam soil sand 15.5; silt 65.5; clay 18.0; organic matter 1.15; pH 8.1; total nitrogen
1.3; assimilable P
2
O
5
35 mg kg
− 1
; exchangeable K
2
O 165 mg kg
− 1
. The soil was characterised by a water table rather superficial with a deph of 120
cm during the driest season. The soil displayed the following hydrological characteristics: field capac-
ity, 27.3 dw, wilting point 9.4 dw.
Meteorological conditions during the seven years of study are shown in Table 1.
The warm-season perennial species used in this evaluation were Ramie, a genotype from Palermo
Botanical garden, and Spanish Broom, one local ecotype. Spanish Broom was transplanted at the
end of April 1992, while Ramie was transplanted at the end of March 1993 Table 2. Stump
sprouting for Spanish Broom and rhizome cut- tings for Ramie were used. During the establish-
ment year, plants were cut at the end of the growing season to allow the vegetative regrowth
in the second year.
The experiment was laid out in a randomised block design with four replicates. Plot size was
48 m
2
. In Ramie they consisted of 16 rows, each 6 m long, with an interrow and interplant spac-
ing of 0.5 m. For Spanish Broom a plant den- sity
of 2
plants m
− 2
0.1 × 0.5 m
was adopted and each plot consisted of 8 rows, each
6 m long.
Table 1 Climatic conditions during trials in 1992–1998 and 1918–1982 mean values
S O
N D
F M
A M
J Years Months
J J
A Rainfall
mm 115.7
191.4 50.6
87.3 15.0
17.5 1992
82.5 45.0
101.8 79.4
18.8 60.6
78.7 36.0
130.2 34.1
0.0 166.0
3.9 1993
13.2 65.1
32.2 2.1
2.6 192.3
91.4 122.9
84.1 21.4
2.0 1994
123.3 58.2
22.3 62.4
1.5 0.8
25.4 88.6
58.4 1995
108.1 71.6
8.2 101.2
2.1 40.6
91.1 136.4
56.8 114.5
2.8 224.6
122.6 77.5
16.1 83.1
49.7 44.5
12.2 98.1
91.7 1996
45.9 37.5
82.4 95.6
21.3 1997
21.1 118.0
55.0 25.0
58.4 7.2
0.0 98.2
95.3 42.2
56.6 56.9
49.0 49.0
1998 24.2
73.6 44.8
1.7 8.8
118.0 99.0
79.0 80.0
1918–1982 83.7
134.2 42.0
89.0 25.0
46.4 67.2
77.5 Temperature min.
°C 2.9
12.9 8.9
4.9 1.6
4.8 7.5
12.3 14.9
17.2 18.9
1992 15.0
2.2 9.5
6.3 6.4
− 0.7
2.2 7.6
11.5 16.2
16.2 19.1
1993 15.7
9.9 5.3
16.9 20.1
18.7 11.6
15.3 1994
12.5 7.5
6.9 3.1
4.4 14.4
11.8 5.9
5.2 1995
3.7 0.5
3.2 8.1
11.6 13.4
18.9 17.9
9.2 4.9
1996 13.1
17.2 10.9
17.1 5.3
15.5 11.9
8.7 4.1
2.0 11.1
4.5 8.1
4.1 7.5
4.6 5.7
12.0 16.6
16.5 19.1
15.9 1997
14.1 11.2
4.9 1.5
2.6 3.0
3.0 1998
10.5 3.6
14.4 16.3
17.8 6.9
3.7 15.0
17.2 14.8
1918–1982 11.0
2.8 17.0
2.3 5.3
8.1 11.6
Temperature max °C
11.9 20.5
17.3 12.7
13.4 15.6
17.5 24.0
24.3 27.5
29.7 1992
25.8 12.1
18.0 14.5
14.2 13.3
13.9 17.4
22.8 27.9
28.2 31.3
1993 25.9
18.4 12.5
26.1 31.0
31.1 21.8
26.1 1994
22.5 17.7
17.6 12.7
13.7 11.1
23.1 15.6
12.8 13.3
13.8 18.0
21.1 23.8
29.8 28.6
1995 23.9
16.5 12.4
12.6 1996
23.7 21.1
28.8 11.3
28.3 27.0
21.6 17.9
14.3 21.6
13.7 16.1
13.1 10.8
17.9 17.4
23.2 25.7
28.0 30.8
27.7 1997
24.9 21.1
14.1 10.5
15.0 1998
15.8 12.9
15.8 23.3
26.4 28.8
29.4 26.2
21.3 15.8
12.0 1918–1982
12.7 11.2
15.1 18.3
22.4 26.1
29.1 29.2
Table 2 Dates of vegetative regrowth and of harvest for Ramie and Spanish Broom at Pisa in the different years of growth
a
Spanish Broom Ramie
Year C2
C3 VR
H VR
C1 1992
10 May –
1993 08 August
18 April 21 October
03 April 11 September
– 18 October
04 April 18 October
24 August 1994
21 June 01 March
19 September –
03 April 1995
22 October 26 February
10 July 1996
02 December 01 March
06 April 05 November
12 June 05 September
25 November 27 March
24 October 18 September
18 February 09 July
1997 15 September
– 26 March
1998 29 September
01 March 08 June
a
VR, Vegetative regrowth; H, Harvest; Ramie was transplanted on 23 March 1993 and Spanish Broom on 23 April 1992; C1, C2, C3, first, second, third cutting.
In order to evaluate maximum crop yield, plants were maintained in optimum water supply
conditions. All plots received the same amount of N, P, and K: 100 Kg ha
− 1
per year. The nitrogen dose was split into two equal pre-planting and
late-spring applications. During the second and the third growing seasons, plots received only 50
Kg ha
− 1
of N in a single dose at the end of winter. Plots were kept weed free by hand hoeing.
The establishment year was not considered and crops were tested starting from the second grow-
ing season. Screening of these species for pheno- logical and biometrics characteristics as well as
for above-ground biomass and stem production was carried out from 1993 to 1998. Cycle length
was measured as the number of days from vegeta- tive regrowth to harvest.
Biometrics and productive determinations were performed on a minimal area of 6 m
2
in the inner part of each plot. According to Iyengar and Bhu-
jang 1961 Ramie harvests were usually accom- plished when the lower part of the stem was
turning brown. Spanish Broom was harvested only once in autumn and plants were cut at 15 cm
from the soil. Aerial dry matter was separated in the different plant organs. The useful part was
represented by stems without cymes and leaves for Ramie and by new branches for Spanish Broom.
After harvest, all plants in the plots were cut 10 – 15 cm above ground for allowing uniform
vegetative regrowth.
Both species were harvested by hand. Spanish Broom new branches and Ramie dry stalks, with
leaves and cymes removed, were decorticated us- ing a small decorticating machine in order to
remove the outer barkepidermis and the bast from the woody core of the stems. Several stalks
were passed through fluted crushing rollers at the entrance to the machine. Stalks were thereby con-
strained as their full length was decorticated in one pass through the machine. During this opera-
tion the cortex, comprising the bast and outer bark, was removed from the stem. The cortex was
scraped to remove most of the outer bark and the parenchyma in the bast and, for Ramie, some of
the gums and pectin. After decortication the fibres were hand brushed for make them suitable for
physical and mechanical testing.
2
.
2
. Morphological, chemical and mechanical characterisation
Fibre bundles were confined in small plastic sleeves and then cross-sectioned. Scanning mi-
croscopy SEM was carried out on gold coated cross-sections.
X-Ray patterns were recorded using Ni-filtered Cu – K radiation from a Siemens 500 D diffrac-
tometer equipped with a scintillator counter and a linear amplifier.
Fourier-transform infrared
spectroscopy FTIR spectra were obtained with a Bruker IFS
66-FTIR spectrometer on samples dispersed in KBr; 32 scans were accumulated for each sample,
with a resolution of 4 cm
− 1
. In accordance with the TAPPI OM 250
method, the lignin content was determined as the sum of insoluble and soluble lignin, the latter
being determined spectrophotometrically at 205 nm.
Pentosan content was determined according to the TAPPI T 223 hm 84 and ash content accord-
ing to the TAPPI 15 OS 58 method. The TAPPI 284 OM 82 method was used to
assess the extractives content and the UNI 8282 method to determine the degree of cellulose poly-
merisation in cupriethylenediamine CED after delignifying the material with sodium chlorite.
2
.
2
.
1
. Fibre strength The tensile properties of selected filaments were
determined with an Instron 1185 load cell 10 N at the cross-head speed of 2 mmmin at room
temperature 20 9 2°C and 70 9 5 relative hu- midity. Since the diameter of filaments, particu-
larly for Ramie, was not uniform, selection of suitable samples was made with the help of a low
magnification microscope; the diameter for each filament was taken at different places with the
help of a precision gauge meter and the average value was used. Diameters were found to vary in
the range 40 – 60 mm. Unlike man made fibres for composites, Ramie and Spanish Broom fibres are
not circular. The diameter referred to in this work is that of the circle of the same area as the
vegetable filaments.
The elastic modulus E was measured by the slope of the conventional stress-strain curves tak-
ing the distance between grips as the gauge length. To measure the strength of fibres different
gauge lengths were used, in the range 10 – 50 mm; a minimum of 50 filaments was taken for each
gauge length to give data statistical meaning.
2
.
2
.
2
. Single fibre composite SFC
tests A silicon rubber mould was used to make dog-
bone shaped single fibre coupons approximately 60 mm long, 10 mm wide, 1 mm thick. Filaments
were selected as to assure their diameters were similar : 50 mm.
The epoxy resin was a bifunctional bisphenol-A type with an epoxy equivalent of : 195 Epikote
828 by Shell. The hardener was p-amine-dicy- cloexyl-methane, used at the content of 25 by
weight. Resin and hardener were intimately mixed at room temperature and freed from air bubbles
by degassing at 50°C for 10 min in a vacuum oven. The mould containing the filaments was
also equilibrated at 50°C prior to resin pouring. The casts were cured at 70°C for 2 h and post-
cured at 100°C for 3 h.
The coupons were slowly strained in an Instron tensile machine 1185 at the crosshead speed of
0.02 mmmin. The fragmentation of the fibre was observed by means of a microscope attached to
the machine, at magnification 40, both in natural and polarised light. The fragment lengths were
measured by the help of a calibrated eyepiece. Tests were repeated with identical coupons to get
at least 100 fragments for collecting a reasonable number of fragments.
The interfacial strength of HS-Carbon fibres and of E-Glass fibres was measured, for compari-
son, using the same epoxy resin as the matrix.
3. Results and discussion
