Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 555-561
Summary The objective of this work was to alleviate the electrical hazards through gasification of the fibers. To this end, a series of experiments were conducted beginning with graphite fiber tows and culminating in composite panels. These experiments demonstrated that calcium acetate was a powerful oxidation catalyst for graphite fiber. In tests on composite materials, combinations of lithium acetate and calcium acetate proved not only to be good catalysts, but also caused little or no degradation in mechanical properties. The service life of the composite was not reduced by the catalyst addition, unless high moisture conditions exist. In those situations, the use of water-insoluble acrylate compounds should be explored. The ultimate test of the modified composite is how it performs in a crash-free situation. In a small-scale simulator developed by JPL, the catalyst-treated composites released very few conductive fibers when compared to state-ofthe-art composites. In addition to achieving the stated objective, this research produced information useful in the general field of carbon combustion. One area which has been examined since the completion of this work is coal combustion. The use of catalysts should result in smaller furnaces for a given throughput and reduced pollution as a result of decreased combustion temperature. Another area is the reduction of carbon particulates from diesel exhaust. One potential method of particulate destruction would use the technology developed in the grid detector system to electrically initiate
555
combustion. This technique could be used for any carbon particulates.
Literature Cited Baker, R. T. K.; Thomas, R. B.; Wells, M. Carbon 1075, 13, 141-145. Baker, R. T. K.; Sklba, T., Jr. Carbon 1077, 15, 223-237. Carbon Fiber Risk Analysis. An lndustrylgovernment briefing held at Langley Research Center, Hamton, VA; NASA Conference Publication 2074, 1979a. Assessment of Carbon Fiber Electrical Effects, NASA Conference Publication 2119, 1979b. Day, R. J.; Walker, P. L.; Wright, C. C. "Industrial Carbon and Graphite", Society of Chemical Industry: London, 1958; p 364. Gibbs, H. H.; Wendt, R. C.; Wilson, F. C. Roc.,Annu. Conf., Reinf. P/ast.l Compos., Inst., Soc., Plast. Ind. 1078. 33. Humphrey, M. F.; Dowler, W. L.; Ramohaiii, K. N. "Gaslflcatlon of CarbonGraphite Fibers", Patent Application, US. No. 30836, filed Apr 17, 1979. Krylov, 0. "Catalysis by Nonmentals", Academic Press: New York, 1970; p 20. Ramohalll, K. N. "Novel Approaches for the Alleviation of the Electrical Hazards of Carbon-Fiber Composites", JPL Publication No. 79-63, 1979. A Report of Observed Effects on Electrical Systems of Airborne CarbonlGraphite Fibers, NASA TM78652, 1978a. Intergovernmental Committee, Compliers: Carbon Fiber Study, NASA TM78718 1978b. Time, "Peril From Superplastlcs?" Mar 13, 1978, 90. Yang, L. C. "High Voltage Spark Carbon Fiber Detection System", JPL Publication No. 80-30. 1980.
Received for review January 12, 1981 Revised Manuscript Received May 8, 1981 Accepted May 8, 1981 The search described in this paper was carried out a t the Jet Propulsion Laboratory, California Institute of Technology, under NASA Contract NAS7-100.
New Composite Materials from Natural Hard Fibers Hector Belmares, Arnold0 Barrera, Ernest0 Castlllo, Etlenne Verheugen, and Margarlta Monjaras Centro de Investigacion en Quimica Aplicada, AMama Ote. 371, Saltillo, Coahuila, Mexico
Georges A. Patfoort and Moniek E. N. Bucquoye Nationaal Hoger Instituut voor Bouwkunst & Stedebouw, Antwerpen, Belgium
Natural hard fibers in many countries are a clear type of a regressive industry. However, their main advantages, namely, a relatively high tensile modulus, a low elongation at break, and being themselves a renewable resource, have not been duly considered in the past. We found that sisal, henequen, and palm fibers have very similar physical, chemical, and tensile properties and this could be true for many other natural hard fibers in the world. Systematic studies were carried out to develop composite materials based on palm fibers. The results are readily applicable to many other natural hard fibers in the world. Among the variables studied were: fiber length, fiber content, fiber coating content, number of fiber plies, palm-glass fiber combinations, three different polymeric fiber coatings, and selected formulations of a polyester resin. Resulting tensile and flexural properties are discussed. The strength/price ratio was favorable to the natural fiber composites.
Introduction The Dresent trend in the USA and elsewhere is to find economically useful industrial applications to readily available renewable raw materials. With this objective, the governments of Mexico and the United States are individually and cooperatively planning and instituting programs in two important areas. The first involves the systematic assessment of indigenous plant species for 0 196-432 1/ 8 1/ 1220-0555$0 1.25/0
economically useful raw materials and the second involves actions to combat the destruction or desertification of these vast land areas. Along the lines of the first area, some recent studies and developments have already been published (Belmares et al., 1979a and 1980, with references therein). At the present time, we are also studying systematically new economically sound applications for natural hard fibers; among them are sisal (Agaue sisalana, a 0 1981 American Chemical Society
556
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 3, 1981
cultivated plant), henequen (Agaue fourcroydes, a cultivated plant) and palm fibers (Yucca carnerosana, a wildly growing plant). The three kinds of fibers have been found to be very similar to each other in their physical, chemical, and tensile properties as we will see later, and indeed they are also similar to many other natural hard fibers in the world. The total production per year in Mexico for palm and henequen fibers is about 105OOO tons. They form part of regressive industries in the Chihuahua dessert (shared in common with USA) and southern Mexico. The traditional uses for all natural hard fibers in the world have been in textiles, agricultural twines, brushes, etc. (Barkakaty, 1976). However, these industrial applications are not sufficient to improve significantly the poor socio-economical condition of the people involved in the gathering and selling of fiber products due to the severe competition from man-made fibers and to backward production technology. These facts make this fiber industry a regressive one in about every country involved. Due to this general trend, the selling price of these fibers is relatively low, and as an example, palm fibers are sold at $0.12 (U.S. dollars) per pound. Looking for definite fiber properties that would be an asset to these fibers, we found that surprisingly the fiber stiffness (high tensile modulus, low elongation at break) and relatively low density (1.4 g/cm3 vs. 2.5 g/cm3 for glass fibers) were properties not as yet fully exploited. We believe that one of the best applications, technically and economically speaking, is in the field of composite materials. Because of these reasons, we started an in-depth research program to develop composite materials that incorporate natural hard fibers, and later on a cooperative program with UNIDO (United Nations Industrial Development Organization) was signed through the auspices of the Council for Science and Technology (CONACYT, Mexico) for the development of composite materials (plastics and others) based on natural hard fibers to be used as building materials (sorely needed) in a variety of applications such as roofs, silos, low-cost housing, and other applications. Early initial attempts to build low-cost housing with a combination of jute and glass fiber-reinforced polyester are described in the literature (Winfield and Winfield, 1975). We wish to report in this paper our present systematic studies to develop composite materials based on natural hard fibers. The work was done with palm fibers, but the results can be just as well extended to other similar fibers such as sisal, henequen, jute, etc. Additionally, intensive studies and tests continue for the industrialization of these composite materials.
Experimental Section Fiber Obtainment. The fibers were obtained from Yucca carnerosana plants located in and around the State of Coahuila, Mexico. The upper central part of Yucca plants was boiled in water and then hand-scrubbed to obtain the fibers; these were air dried (to an equilibrium humidity of 5-7% by weight of fibers), and then kept in a dry and dark place. Materials. Polyester resin (PER) Polylite 8016 was obtained from Reichhold Quimica de Mexico, Mexico, D.F. It is a resin of medium reactivity, composed of phthalic anhydride, maleic anhydride, and dihydric alcohols. It has a viscosity of 1290-2270 CPat 100% solids, 77 OF, and 85-150 CPat 75% solids (in styrene monomer) at 77 OF. The USA counterpart has a viscosity 2700-3700 CPand 150-200 CPat 100% and 75% solids, respectively, at 77 OF. As a reference, a 70% resin solids in styrene monomer (Polylite 8016) with 1% catalyst methyl ethyl ketone (MEK) peroxide (60% solids) and 0.5% promoter cobalt
naphthenate (CoNaph) solution (6% Co metal) has a gel time of 15-20 min. Both catalyst and promoter solutions were also obtained from Reichhold Quimica de Mexico. Styrene monomer (Sty) was received from Union Carbide of Mexico, Mexico, D.F., and was used without further preparation. Glass mat (E-glass) was supplied by Vitrofibras de Mexico, Mexico, D.F. (subsidiary of Owens Corning Fiberglas); the mat has a weight of 458 g/m2. Poly(viny1alcohol) (PValc) (99-100% hydrolyzed) of high molecular weight was obtained from J. T. Baker Chemical Co., Phillisburg, N.J., with a viscosity of 55-65 CPfor a 4% aqueous solution at 20 "C. Poly(viny1 acetate) (PVAc) emulsion (Polyco 804-P) was obtained from Industrias Quimicas Formex (Borden Chemical), Monterrey, Mexico. PVAc emulsion is a vinyl acetate/fumarate copolymer used as a base for exterior and interior paints; solid content: 55 f 0.5%; particle size: 0.2-0.4 pm; pH at 25 OC: 4.0-5.0. Gantrez AN-139 was received from GAF Corporation of Mexico, Mexico, D.F. I t is a water-soluble interpolymer of methyl vinyl ether and maleic anhydride (one to one molar ratio of vinyl ether to anhydride), specific viscosity of 1.0-1.4 in MEK at 25 "C (1g of copolymer in 100 mL of MEK). Lastly, the 2-hydroxyethyl methacrylate (HEMA) monomer was supplied by Aldrich Chemical Co., Inc., of Milwaukee, Wis., and has a bp of 67 OC/3.5 mm and a nD of 1.4515 at 20 "C.It was used without further preparation. Polyester Laminates Manufacture. Multiple ends of palm fibers are cut to the desired length (generally 6 cm) and then accommodated at random to form 20 X 20 cm squares of a previously chosen weight (generally 12,18, or 24 9). An aqueous solution (PVAlc, Gantrez) or emulsion (PVAc) of the binding agent is sprayed uniformly to the samples. The water is allowed to evaporate partially, at room temperature, and then the samples are pressed at 50 lb/in.2 at 60 OC. During the pressing, the remaining water evaporated off almost completely (15 to 30 min). The nonwoven fabrics (mats) are conditioned for 24 h before the initial tare and before the final weighing. The difference between the initial and final weighings is considered the dry weight add-on. Normally, the mats have 7% of moisture content before the initial tare and before the final weighing. To make polyester laminates, standard hand lay-up techniques were used (Winfield, 1969). The given PER and Sty composition was catalyzed with 190 MEK peroxide solution and 0.5% cobalt naphthenate solution. The catalyzed resin is brushed on a mold. A fiber mat is laid on the wet mold. Air is worked out by brushdabbing. After the resin soaks into the reinforcement, subsequent layers are built up to the required thickness and are cured at room temperature. A constant pressure of 0.3 lb/in.2 is kept upon the aggregate. Cellophane was used as a mold release agent. Samples were left to stand at least 4 days at room temperature before determining their mechanical properties. Equipment and Test Methods. For the polyester laminates, the tensile strength (kg/cm2), tensile modulus (kg/cm2),and % elongation-at-break were determined following the ASTM D638 test method. The average scattering of the mean values is *lo% and f7% for the tensile strength and the tensile modulus, respectively. For each of the Figures 1 through 5, the mean fiber vol. 5% f average scattering is listed in the corresponding figure captions or in the Figure itself (Figure 1). For the determination of flexural strength (kg/cm2) and flexural modulus (kg/cm2), the ASTM D790-71 test method was followed. The average scattering of their mean values is i8% and *IO%, respectively. The energy to break
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 3, 1981 557 N
E 2
1
600
1 OI
1-
I
-
0 +
Z
u c [L ln
2001 c
0
a
8
16 24 32 FIBER VOLUME, O / o
40
FIEER VOLUME, %
Figure 1. Tensile properties of palm fiber composites aa a function of the fiber content. Fiber coating: 5% PVAlc. One fiber ply of 450 g/m2. Resin formulation: PER/Sty = 50:50.
Table I. Comparison of Physical and Chemical Properties of Palm (Yucca carnerosana), Sisal (Agave sisalana), and Henequen (Agave fourcroydes) Fibers palm fibers fiber diameter, mm fiber length, m single ultimate cell diameter (major axis/ minor axis), pm lignin, % cellulose, % hemicellulose, % porosity,f %
0.15-0.25
sisal fibers
henequen fibers
0.13-0.5a
0.13-0.5O
0.3-0.6 0.6-1.5" 0.6-1.5' 18 (average)b 15.8/10.8a 22.2/11.6O
not det. 50-60d 24e
8c 78c
10
not det.
1oc
13" 50-60d 21e not det.
a Kirk and Othmer (1955). Ballesteros (1946). From cellulose trinitrate derivaBarkakaty (1976). tive. I t was made by a slight modification of already reported techniques (Alexander and Mitchell, 1949; Chang, 1972). Gel permeation chromatography determination ofthe cellulose number-average degree of polymerization (DPn) gave values from 500 t o 900 (Flores e t al., 1975). e From gas chromatography analysis of the alditol acetates obtained by acid hydrolysis of the fiber hemicelluloses followed by reduction (Sweley e t al., 1963) and acetylation of the monosaccharides (Borchardt and Piper, 1970) t o obtain the alditol acetates. The monosaccharides arabinose, xylose, mannose, and galactose were identified and quantitatively determined (Maldonado, 1978). f Glycerine retention value (GRV). Glass fibers gave a GRV of 1 0 while cotton gave a GRV of 92 (Belmares e t al., 1979).
Table 11. Comparison of Tensile Properties of Palm, Sisal, Henequen, and Glass Fibers palm fibers U
9 FIBER LENGTH, cm
3
6
12
N
-
.o / o -
0
1
10
0
b
3
6 9 FIBER LENGTH, cm
12
N
-
'0
r
/
,/ m
e
6 1
/o
c
0
3
6
9
12
FIBER LENGTH, c m
Figure 2. Influence of the fiber length on the tensile properties of palm fiber composites. Fiber coating: 6% PVAlc. Three fiber plies of 450 g/m2 each. Composite fiber content; vol. %: 36 k 4%. Resin formulation: PER/Sty = 6040.
(kg/cm2) was calculated from the area under the tensile curve. Average scattering is f17% of ita mean value. The tensile and flexural properties of the polyester laminates were determined in an Instron Tester Model 1122 at 23
glass fibersb
Seymour (1969-1970).
"C and 50% relative humidity with a sample conditioning of no less than 40 h. For the palm fibers, tenacity (breaking load/unit linear density, in g/denier), % elongation-at-break, and tensile modulus (g/den) were also determined in the mentioned testing machine and under the same sample conditioning. The following conditions in the Instron Tester were used: gauge length, 7 cm; chart speed, 10 cm/min; crosshead speed, 10 cm/min; full-scale load, 5000 g; number of single-fiber determinations for the tensile properties, 60; average scattering for the mean values of the tensile properties, 30%; average fiber denier, 265; average fiber diameter, 0.16 mm. When needed, a palm fiber density of 1.4 g/cm3 and a glass fiber density of 2.5 g/cm3 were used to transform g/denier to kg/cm2 (or conversely). For the cost considerations, a selling price (in Mexico) of $3.25 (US. dollars) per kilogram was used for glass fibers (in mat). Results and Discussion Fiber Characterization. Palm fibers were characterized and compared in their physical, chemical, and tensile properties to other very well known natural hard fibers and to glass fibers. All this is shown in Tables I and 11. From these tables it is concluded that palm fibers are practically
*
/
z Y
henequen fibersa
tenacity, g/den 4.4 4.1 4.7 12.5 (kg/cm2) (5554) (5166) (5922) (28169) elongation at 3.3 2.8 4.7 3.0 break, % tensile 113 135 103 329 modulus, (0.14) (0.17) (0.13) (0.74) g/den ( 1O6 kg/cmz) a Nilsson (1975).
11 t
sisal fibersa
558
Ind. Eng.
Chem. Prod. Res. Dev., Vol. 20,
No. 3, 1981
,
C C
3
1
3
2
15
12
6 9 ADDITIVE, %
4
NUMBER OF FIBER PLIES
3
6 9 1 ADOITIVE. %
2
5 ADDITIVE, %
10
1
5
L 1
2 3 4 NUMBER OF FIBER PLIES
c I
2
3
4
NUMBER OF FIBER PLIES
Figure 3. Influence of the number of plies on the tensile properties of palm fiber composites. Fiber coating: 6% PVAlc. Each fiber ply is of 300 g/m2. Composite fiber content, vol. %: 18 f 2%. Resin formulation: PER/Sty = 5050. Zero ply points correspond to actual properties of the polymerized resin itself.
equal to either sisal or henequen fibers and that any industrial application found for palm fibers can be also applied to the other two fibers. Moreover, we believe that the present development in composite materials can be just as well extended to many other natural hard fibers. From these tables it can also be seen that natural hard fibers are inferior in tensile strength and modulus to commercial glass fibers. However, we must point out that the selling price in Mexico for a unit volume of glass fibers is 20 times higher (and growing) than the selling price for the same unit volume of palm fibers. Under these conditions, the strength (kg/cm2)/price ratio for palm fibers and glass fibers is approximately 2; i.e., reinforcing glass is twice as expensive in relation to its strength. In terms of the unit weight of the fibers, the corresponding strength (g/ den)/price ratio is approximately 4. Additionally, compositions have been developed to make the natural hard fibers more resistant to biodegradation (Belmares et al., 1979b) in an effort to tilt even more the overall balance in favor of the vegetable fibers. Polyester Laminates. These laminates are intended to be manufactured industrially in a continuous process that implies the winding of the fiber reinforcement in the manner of a continuously bonded closed helical spring around a rotating mold, previous impregnation of the fiber reinforcement with a catalyzed PER-Sty formulation (or any other appropriate formulation), followed by the curing of the latter one at room temperature. Initially, we studied in the laboratory the woven fabric made with palm fibers as a possible reinforcement for the polyester laminates.
15
Figure 4. Influence of fiber additive (coating) content in palm fiber composites. For PVAlc (-O-) coating the composite is defined as follows: fiber content (vol. %), 25 f 1.5%; one fiber ply; resin formulation, PER/Sty 5050. For PVAc (- -v--) coating the composite is defined as follows: fiber content (vol %), 25 f 3%;one fiber ply; resin formulation, PER/Sty 5050; ply weight: 450 g/m2.
0
210
i
/
1
N
350C
$ L +
,A.
I
5
10
15
ADDITIVE, %
Figure 5. Flexural strength (- -0--) and flexural modulus (-O-)as a function of the fiber coating (PVAlc) content in palm fiber composites. Fiber content, vol. %: 25 f 1.5%. One fiber ply. Resin formulation: PER/Sty = 50:50.
However, the woven fabric was found unsatisfactory because of the poor tensile properties of the laminates sometimes even inferior to the values of the cured unreinforced resin. This is due to two factors; firstly, the twist that the fiber strands must have before weaving (about 2l/, turns/in. due to the discontinuous character of the fiber) making it difficult for the PER-Sty formulation to penetrate and wet all the fibers of the fiber strand, with an even less penetration if a polymeric interfacial agent is added to the woven fabric; and secondly, the weaving process damages the fibers which lose up to 70% of their initial tenacity by the time the woven fabric is made. Therefore, to avoid all these problems, nonwoven fabrics were chosen
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 3, 1981 559
instead as the laminates reinforcements. Fiber Binding Agents for Nonwoven Fabrics. It is generally accepted that in fiber-reinforced composites, the fiber-matrix interface plays an essential role in determining the mechanical properties. At the interface, loads are transferred from the matrix to the fiber. This load transfer is dependent on fiber-to-matrix adhesion and on the fiber aspect ratio (fiber length/diameter) (Cooper et al., 1976). Therefore, two important factors had to be considered in the present work; the first one was the choice of a good binding agent to make the nonwoven pressed fabric with the consequent decrease of the volume occupied by the fibers (the latter factor being very important to obtain composite materials of high fiber content); and the second, the choice of a good interfacial agent. To simplify the problem we chose to have in the same agent both properties, that is, good binding and good interfacial properties. Three different polymeric binders were chosen for studies as interfacial agents, namely, polyvinyl alcohol (solubility paramter 13.41, poly(viny1acetate) (solubility parameter 9.351, and Gantrez AN-139. The PVAlc and Gantrez AN-139, being water soluble, were applied to the fibers as aqueous solutions, while PVAc was applied as an emulsion in water. When Gantrez AN-139 is dissolved in water, some of the anhydride groups are cleaved to give the free dicarboxilic acid (GAF Technical Bulletin). Therefore, the PVAlc and the Gantrez AN-139 have functional groups that are able to form hydrogen bonds with the hydroxyl groups of the hemicellulose, cellulose and lignin components of the vegetable fibers. The use of aqueous solutions of PVAlc and Gantrez AN-139 should provide a good wet-out of the vegetable fibers by each of the mentioned polymers since the fibers are hydrophilic. A good fiber wetting by the added polymers should give a nonwoven fabric with a uniform distribution of these polymers (important factor for a good interfacial agent) and also a nonwoven fabric with good tensile strength properties (due to an acceptable binding performance of the added polymer) (Redshow, 1979). Indeed, the PVAlc, Gantrez AN-139, and PVAc gave nonwoven fabrics with acceptable strength properties at levels from 6 to 15% (dry weight basis of fibers). On the other hand, nonwoven fabrics bound with PVAc or with Gantrez AN-139 lost strength and coherence when placed in contact with PER-Sty formulations (in 15-30 min) but the PVAlc-bound fabric was not affected even after several hours. This behavior is due to the solubility of PVAc and Gantrez AN-139 in PER-Sty formulations while PVAlc is practically insoluble in those formulations. The behavior of the three polymeric binding agents as interfacial agents was carried out and the results will be discussed next. Tensile and Flexural Properties of Polyester Laminates. In Figure 1 it is shown that for the palm fiber composites the tensile properties are directly proportional to the volumetric fiber concentration when PVAlc is used as the interfacial agent. This fact indicates that there is bonding between the fiber and the resin. Indeed, in the absence of bonding, the fibers would act as voids and therefore would be stress concentrations, thereby greatly diminishing the tensile strength of the specimen. Figure 1also shows that at volumetric fiber concentrations of less than 20% (for one fiber ply) there is not significant reinforcement. We must point out that if the fibers did not have any binding agent and were not pressed, the upper fiber concentration allowable would be around 20% due to the low density of the fiber mat. One possible failure mode of fiber reinforced composites is fiber pull-out, which results from interfacial bond failure,
and a second mode is fiber fracture (Cooper et al., 1976). For the three fiber coatings studied, the corresponding composites show fiber fracture as the mode of failure. Figure 2 shows the effect of fiber length upon tensile properties of composites. Fiber fracture is observed for all the fiber lengths tested. No significant improvement in tensile properties was obtained when the fiber length exceeded 9 cm. Since fiber fracture instead of fiber pull-out is observed, the increase of the composite tensile strength with fiber length is not due to having the fibers below their critical length but to other unknown factors. Incomplete fiber wetting is not the determing factor for this composite behavior either, because incomplete complete fiber wetting would favor a fiber pull-out failure mechanism. Thus for synthetic fibers, composites expected to fail by fiber fracture have been found to fail by fiber pull-out; that is, at the interface, frictional shear strength instead of interfacial bond strength is a controlling factor of tensile strength in the studied composites possibly due to incomplete wetting of the fibers among other factors (Cooper et al., 1976). For palm fiber composites, incomplete fiber wetting (by lack of brush-dabbing during PER mat soaking) brings about 50% decrease in flexural strength and flexural modulus and about a 30% decrease in tensile strength. For the palm fiber composites, the number of fiber plies in the laminate has an influence in the tensile properties as is shown in Figure 3. Increasing the number of plies brings an increase in tensile properties. This effect is expected because failure of a critically stressed layer (or group of layers) in the composite does not necessarily mean that total catastrophic failure of the multilayered composite takes place because the latter will still retain a significant amount of load carrying ability until all the composite fails (Grinius and Noyes, 1969). Possibly the ply effect is stronger with palm fibers than with glass fibers because the diameter of the former ones is far greater than glass fibers, the palm fibers therefore having a smaller specific surface for interfacial bonding and less space coverage at equal fiber volumes. The quantity or surface concentration of the PVAc or PVAlc fiber coatings also affects the mechanical properties of the palm fiber-resin composites. The effect is illustrated in Figures 4 and 5. It is similar to the effect found on the glass fiber-resin composites when appropriate silanes are added to the glass fibers (Wong, 1972). In all cases, the given composite properties go through a maximum when they are plotted as a function of the interfacial agent concentration. In order for the fiber and resin to come into close contact it is apparent that the resin must cover up every hill and valley of the microscopically rough fiber surface and displace all the air and that no weak boundary layer is formed. These conditions are satisfied if good resin wetting of the fiber is obtained; that is, the finish applied to the fiber surface has to act as a wetting promoter (Yip and Shortall, 1976). To investigate this point, several formulations were studied: (a) PER/Sty ratios of 5050,6040, and 7030 were used with both, PVAc and PVAlc fiber coatings. (b) Sty was partially substituted with HEMA, CH2=C(CH3)COO(CH,),OH, to make resin formulations PER/Sty/HEMA such as 50:45:5, 50:4010, 60:35:5, 60:30:10, and 70:25:5. HEMA is totally miscible with PER/Sty compositions (and water), it is hydrophilic, it copolymerizes with PER/Sty formulations, and it is potentially able to form hydrogen bonds with the lignin, hemicellulose, and cellulose of the fibers. Both PVAc and PVAlc coated fibers were used with these formulations. (c) Gantrez AN-139
500
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 3, 1981 N
I
200 LOO 6W 800 TENSILE STRENGTH, k g / d
Figure 6. Relationship between tensile strength and tensile modulus for a large variety of palm fiber composites. It includes PVAc, PVAlc, and Gantrez AN-139 coatings. Correlation coefficient: 0.71. I
N
I
l
0
200 400 600 800 TENSILE STRENGTH. k g d
Figure 7. Tensile strength vs. energy to break for the composites of Figure 6. Correlation coefficient: 0.93. 0
~
____
~
I
'CCZ F-EXLR,.
O"*id""
150:
23OC
h s rrr2
Table 111. Comparative Mechanical Properties of the Glass Reinforced Composites and a n Unreinforced Cured PER Formulation sample no." fiber type fiber coating fiber content, vol. % resin formulation, PER/Sty/HEMA tensile strength, kg/cm2 tensile modulus, l o 3 kg/cm2 flexural strength, kg/cm2 flexural modulus, l o 3 kg/cm2
152 none
148 glass silanes 0 27 50:50:0 60:40:0 381 9.8 notdet. not det.
1639 26.7 3627 162.3
a Three fiber plies were used in all cases. mat.
150 glass silanes 20 70:30:0 1090 32.3 3528 292.0
As fiber
Table IV. Comparative Mechanical Properties of Palm Fiber Reinforced Composites with Two Different Fiber Coatings
0'
L
STQEhGTP
Figure 9. Tensile strength vs. flexural strength for the composites of Figure 8.
sample no." fiber type fiber coating; % L
1202
TEhSlLE
~
~
-
50C
xrc
S'
