Research into the specifications of woven composites obtained from raffia fibers pretreated using the ecological method

Abstract

Studies on using cellulosic natural fibers as reinforcement for composites are rapidly growing. The aim of this study is using a raffia-based woven fabric as reinforcement for composites that are grown in the Mediterranean Zone of Turkey. These fabrics benefit from their mechanical performances, low density and their biodegradability. However, it is necessary for the fabrics to form adhesion in the matrix. Therefore, chemical processes should be applied onto the surface of the raffia-based woven fabrics. In this study, three different formulations (different concentrations of maleic anhydride, formic acid and acetic acid) were applied by using conventional and microwave energy on the raffia fabrics. At the end of the application, composite structures were formed by using the fabric as the reinforcement layer and isophtalic polyester as the matrix by the vacuum infusion method.

The composite structures were characterized by attenuated total reflectance scanning electron microscope analysis and their mechanical tests were performed through tensile testing.

Considering all results, the combination of acetic acid with the microwave process was found to modify the raffia fabric surfaces.

Keywords

raffia fabric surface treatment microwave method composite mechanical properties polyester resin

Natural resources play a dominant role on the economic activities in the world and they contribute significantly to the gross national product of countries. The recent studies on protection and recycling of natural resources have increased demand for the renewable raw material-based natural materials. Within the scope of using natural sources effectively and environmental protection in the textile industry, the sectors become better with sustainable development strategies. Considering environmental awareness, the use of eco-friendly materials and products is becoming more and more significant every day. Thus, there is a growing tendency for using natural fibers in various fields in the world.¹

Fiber-reinforced composite materials are commonly being used in different fields, such as construction, aircraft, automotive and plastic industries. Reinforcement fibers used to support and strengthen the composite structure are mostly manmade materials such as glass, carbon and aramid, and they have become highly demanded materials due to the high performance they provide at low density. A large number of studies have been performed over the last decade to assess the use of fibers obtained from natural and renewable resources in composite materials.^2,3

The primary goal of the studies is to develop new composite materials that will not cause environmental problems after using them, and increase the use of renewable resources by using fibers with high biodegradability instead of using artificial fibers with low biodegradability; some of the advantages of natural fibers are that they are plentiful, renewable, recyclable, low-cost, low-density, easily processable materials.^4–6

As a result, composite industries are searching for more environmentally friendly materials for composite structures. There is an increasing demand for biodegradable renewable composites reinforced with waste plant fibers. However, certain drawbacks, such as low resistance to moisture and seasonal quality variations (even between individual plants in the same cultivation), greatly reduces the potential of plant fibers to be used as reinforcement for polymers. Natural fibers are hydrophilic in nature, because they are derived from lignocelluloses, which contain polarized hydroxyl groups. Another serious disadvantage is that the high moisture absorption of natural fibers is leads to swelling, which results in poor mechanical properties and reduces dimensional stability of composites.⁷

These fibers, therefore, are inherently incompatible with hydrophobic thermoplastics and thermoset. The disadvantages of using these fibers as reinforcement material in such matrices include poor interfacial adhesion between the polar-hydrophilic fiber and the non-polar hydrophobic matrix, and difficulties in mixing due to poor wetting of the fiber with the matrix.

It is obvious that the mentioned disadvantages can be solved by using chemical treatments. By using chemical modification processes an adhesion property can be obtained between the hydrophilic fibers and the hydrophobic matrix. Chemical treatment of fibers is a common method of cleaning and modifying the fiber surface in order to lower the surface tension and enhance the interfacial adhesion between a natural fiber and a polymeric matrix.⁸ In the economic aspect, waste natural fibers (flax, sisal, ramie, banana, hemp fibers, etc.) are produced in Europe and Asia in order to be recycled for the industry.⁹

Raffia palm fibers grow in the tropical equator region and there are approximately 28 species. The length of the leaves of the raffia palm (raphia farinifera or R. raffia) may reach up to 18 meters. About 100 raffia fibers are obtained from each branch of raffia palm. In order to obtain raffia of palm fiber, it is harvested by cutting the palm leaves when they are completely grown. The watery part on the surface of the leaf is stripped in order to reach the fibrous internal part, and it is prepared to dry it out. The raffia fibers may then be dyed as per the area of use.^10–14

The number of palm-based trees is about 633,399 in Turkey. Palm trees are cultivated quite a lot in the Mediterranean Region in the south of Turkey. The studies have revealed that palm-based fibers will be an alternative material in the production of cellulose-based fiber-reinforced composite.¹⁵

The studies conducted to expand the area of raffia fiber usage in the industry indicate that the physical properties of the tensile testing¹⁶ and elegance at all show the cellulose I_β with a crystallinity index of 64%, Young’s modulus of 30 GPa, a tensile strength of 500 ± 97 MPa, elongation properties between 2% and 4% and the fiber density of 0.75 ± 0.07 g/cm³.¹⁷ There is a study in which the tensile strength specifications of Raphia vinifera L. (arecacea) fiber have been examined comparatively through modeling.¹⁸

It is being specified that the fiber tensile strength increases and the Young’s modulus and whiteness degree decrease when these fibers are processed with NaOH solution whose concentration was 2.5%, 5% and 10% (by weight) in order to facilitate the use of raffia fibers in composite structures.¹⁹ The water sorption specifications²⁰ and thin layer drying specifications of the same fibers have also been examined.²¹ Microwaves are high-frequency radio waves in the infrared spectrum between 30 MHz and 300 GHz.²²

Utilization of the microwave energy power enables the use of drying, dyeing and printing in many fields of the textile sector due to its ability of fast and cost-saving heating in a short time.²³ In order to apply microwaves to a product, the product will have dielectric loss and dipolar electric loads will occur within the material when an inconstant electromagnetic field is applied.^24,25 Therefore, as water molecules can easily compose dipolar electric loads, structures covering water or structures within aqueous ambient conditions are suitable for heating with microwaves. The microwave energy method is defined as an eco-friendly method as it accelerates chemical processes; it saves energy especially in reactions and has a short processing time. It seems that this method is eco-friendly, especially in textile finishing, dying of polyester (PES),^26,27 coloration of flax and cotton fibers^28,29 and surface treatment of cellulosic and protein-based fibers.^29–37

In this study, waste leaves of palm plants cultivated in the Mediterranean Region of Turkey have been evaluated. Raffia fibers have been obtained from waste palm-based leaf fibers. The obtained fibers have been rendered as a weaving structure. Woven-based raffia has been used as a reinforcement layer. For this purpose, surface modification of raffia-based weaving structures has been performed, adopting two different methods by using three different chemical materials: maleic anhydride, formic acid and acetic acid. The surface modification of fabrics microwave energy method, which is an eco-friendly and time-reducing method, has been used as an alternative to the conventional method. At the end of the application, a composite structure was formed with the fabric layer as the reinforcement and with isophtalic PES as the matrix.

Experimental details

Materials

Fabric

In this study, fabrics obtained from raffia fibers and woven by plain weave have been used (Table 1).

Table 1.

Properties of raffia-based woven fabric

Properties	Value
Thickness	1.8 mm
Density (warp)	(3 threads/cm)
Density (weft)	(4 threads/cm)
Tensile strength	278 N
Elongation	1.78%

Resin

In this study, Polives 701 commercial product, which is a general use PES resin obtained from the Poliya Company, has been used (Table 2).

Table 2.

Properties of the liquid isophtalic polyester resin

Test	Method	Value
Liquid resin properties
Color	Observation	Transparent
Density	ISO 1675	1.04 g/cm³
Jell time	ISO 2535	20'
Test	Method	Pure resin value
Rigid resin mechanical properties
Flexural strength	ISO 0178	160 MPa
Elasticity Modulus	ISO 0178	4360 MPa
Breaking Elongation	ISO 0178	6.90%
Tensile strength	ISO 0527	80 MPa
İzod impact Strength<	ISO 0180	17 kJ/m²

Fiber surface treatment

Raffia-based woven fabric has been exposed to two methods, which are the conventional method and the microwave method, as described in Table 3. The microwave method with Arçelik label MD564 1200 W was carried out at a frequency of 2.45 GHz. The microwave oven had a maximal power of 800 W (High+Medium level) with six discrete settings. The mixtures were placed in a sealed glass vessel and treated by the microwave according to the experimental design.

Table 3.

Experimental methods applied to raffia fabrics

Methods	Solution chemical	Producer code of the solution	Solution con. (%)	Conven. temp. (℃)	Conven. time (min)	Microwave time) watt/min	Rinsing process (25℃,10 min, pH 7)	Dry process
Method 1	Acetic acid	Merck (100056)	30,40,50	20	20	800/1	Distilled water	At room temp.
Method 2	Formic acid	Merck (100263)	30,40,50	20	20	800/1	Distilled water	At room temp.
Method 3	Maleic Anhydride	Merck (800408)	2.5,5,10	20	20	800/1	Distilled water	At room temp.

Composite manufacturing methods

In this study raffia-based woven fabrics were used in composite form following the two different processes and three different chemical surface treatments. Thermosetting isophtalic PES resin was used as the matrix. Composite structures were formed by using the vacuum infusion method.

All the composite panels have been produced by means of a vacuum infusion process, whose layout is given in Figures 1 and 2. For this purpose, for each configuration, a stack of dry reinforcement plies has been laminated over a mould. After the lamination stage, the layout has been completed with the flow media and the infusion network, and finally the mould has been sealed with the vacuum bag. The curing stage of the resin, after the infusion is concluded, has been carried out at room temperature, while the post curing took place in an oven in two sub-stages: at 60℃ for 3 h, 20 min and subsequently at 80℃ for 4 h. The in-mould pressure measured during the infusion stages was equal to 18 mbar. Rectangular 300 mm × 500 mm sheets have been obtained. Subsequent cutting operations have been carried out with the aim to produce specimens suitable for mechanical characterization, in accordance to the related standards.

Figure 1.

Dispersion of isophtalic polyester resin in the vacuum bagging technique.

Figure 2.

Lay-out of the vacuum infusion system.³⁸

Testing and characterization

The tensile strength and elongation properties of raffia-based fabrics were assessed on an Intron 4410 instrument, according to the EN ISO 13934-1/ASTM D 5034 standard. Twenty-five specimens were characterized in both warp and weft directions.

Raffia-based woven fabrics in weft and warp directions reinforcement composite speciemens were cut. After preparation of the cutted samples, tensile strength and elongation tests were carried out according to ASTM:D3039-08.

The attenuated total reflectance-Fourier transform infrared (ATR-FT-IR) characterization of the fabrics has been determined using a Perkin Elmer Spectrum 100 ATR-FT-IR model spectrophotometer. The Fourier transform infrared attenuated total reflection (FT-IR-ATR) spectra were recorded on a Perkin Elmer Spectrum 100 ATR-FTIR model spectrophotometer with accessory diamond. Afterwards, the analysis was performed using a Perkin Elmer Spectrometer (Spectrum 100). The ATR-FT-IR spectrum of althaea fiber was recorded in the range of 4000– 600 cm⁻¹ (resolution: 2 cm⁻¹).

Morphological specifications of the samples have been obtained using a Jeol brand 5910LV (operated at 5 and 10 kV) scanning electron microscope (SEM).

Weight loss

The weight loss was determined on an atmospherically conditioned raffia-based fabric after different treatment processes. The weight loss percentage (W_j) was calculated from the differences in weight using the following equation:

W_{j =} \frac{W_{pre} - W_{after}}{W_{pre}} \times 100 (%)

(1) where W_pre is the weight of the conditioned fibers prior to pre-treatment and W_afte_r is the weight after performed pre-treatment.

Results and discussion

Evaluation of weight loss of raffia-based fabric as the result of chemical modifications

In Table 4, weight loss percentages (%) of raffia fabric as the result of processing with different chemicals and methods are presented. Acetylation is originally applied to wood cellulose to stabilize cell walls, which improves dimensional stability against moisture.³⁹ Surface modification has been performed both with conventional methods and the microwave energy method, and weight loss percentage values of the samples have been more than the sample that has not been subjected to process. Weight loss as the result of surface processing made with maleic anhydride is less. However, in cellulose-based structures the biggest problem in hydrolyzing cellulose with acids can be specified as the hardness of the reaction of crystalline areas congested with dense hydrogen bonds with acids compared to amorphous areas and hemicellulose. Thus, hydrolyzing cellulose with acids is closely related with the crystallinity degree.⁴⁰

Table 4.

Weight loss of raffia-based fabrics for different chemical treatments (conventional and microwave energy)

Chemical treatments (Conventional and microwave energy)	Weight loss %
Chemical treatments (Conventional and microwave energy)	Conventional	Microwave energy
30% acetic acid	6.26	7.3
30% formic acid	5.9	6.2
40% acetic acid	8.5	9.1
40% formic acid	7.6	7.9
50% acetic acid	8.3	8.3
50% formic acid	7.4	7.9
2.5% maleic anhydride	3.5	4
5% maleic anhydride	4.5	5
10% maleic anhydride	4.3	5.4

Conditions: at room temperature.

It is being considered that first the hemicellulose of the fiber is being affected as the result of processing of raffia fabric with acetic acid and formic acid. The most weight loss from the raffia fiber has been obtained by the surface modification, which was carried out under microwave energy by use of 40% acetic acid.

The hemicellulose in the fiber structure of raffia fabric has been removed by acetic acid, and thus cellulose has been converted to hydrocellulose. In addition, as the term is short and rapid by the assistance of microwaves, it can be said that acetic acid has filled the gaps by penetrating the internal structures of the cells and has caused expansion in the morphologic structure of the fiber.⁴¹ As a result of measurements, it has been determined that acetic acid causes expansion of fiber by featuring the expanding property with the assistance of the microwave energy method. Thus, the oil and wax type of wastes removed from the surface of the raffia-based woven fabric caused a decline of the fabric weight.⁴²

Mechanical properties

Figure 3 shows a typical example of the stress–strain curve of raw raffia fiber. This curve shows similar behavior to that of a previous work.^15,16

Figure 3.

Stress/strain curve for a specimen of raffia fiber.^15,16

The tensile strength values of raffia fabrics on which no surface modification has been applied and of raffia fabrics processed with different methods and chemical materials in the waft (90°) direction and weft direction (0°) are presented in Figure 4 and 5. Generally, the tensile strength of fabrics processed with microwave energy in waft and weft directions is better than the tensile strength of fabrics that are not processed or processed with the conventional method. This is because when compared with the conventional method, the microwave energy ensures a uniform heating in a short time and penetrates the molecular structure and carries the chemical material directly to the fiber under aqueous ambient conditions. Therefore, the tensile strength of the fibers processed with microwave energy is better. In the microwave application, the hemicellulose section of fibers of raffia woven fabric of lignocellulosic structure reacted more easily and caused an increase in the hydrophility of the structure. When the tensile strength values are compared to chemical materials being used, a positive effect has not been indicated in respect of tensile strength values in the surface modification made with maleic anhydride. It is known that the structure of maleic anhydride (C₄, H₂, O₃, atoms within) is effective for hydroxyl groups of cellulose fibers and ensures the soaking effect.^43,44

Figure 4.

Warp direction (90°) tensile strength values of raw raffia woven fabric and of raffia woven fabric subjected to chemical modification with different methods.

Figure 5.

Weft direction (0°) tensile strength values of raw raffia woven fabric and of raffia woven fabric subjected to chemical modification with different methods.

However, a decrease being observed in the tensile strength values of fabrics subject to maleic anhydride at concentrations of 2.5%, 5%, 10% in the waft and weft directions (Figures 4 and 5). As the concentration of maleic anhydride increases, it has been observed that it affects negatively the hydroxyl groups located in the cellulose chains of fibers and thus it has caused decreases in tensile strength values.

It is known that the process of lignocellulosic-based fibers with organic acids affects tensile strength values. This is because the acids are reactive to hydroxyzine in lignocellulosic-based structures. Acid molecules directly affect the glycoside bonds of hydronium ions within the cellulose chain. Thus it transforms from macro fibrils into micro fibrils.^45,46

Formic acid and acetic acid among the organic acids being used in the study positively affect the tensile strength of raffia woven fabric. Here, the lignin within the structure of the fibers composing the raffia fabric has partially been dissolved and hydroxyl groups within the lignin have decreased hydrophility within the non-polar hydrocarbon and benzene links.^47,48

When Figure 6 is examined, it is observed that an increase occurs in percentage elongation values while in the weft direction the tensile strength of raffia fabric decreases (Figure 5). This is because the tension in the structure of the fabric is more in the waft direction than the weft direction. Therefore, more flexibility and dynamism is being ensured in weft structures. Macro fibrils in the fiber structure transform to micro fibrils due to the surface morphologies after chemical operations. For this reason, an increase occurs in the elongation values of raffia fabric. Thanks to the microwave effect, the increase has accelerated more. In Figure 7, a decrease is observed in the percentage elongation values in the waft direction. In structures of the waft direction, the load distribution of the fabric is more than the waft structures. Also the perpendicular direction of waft structures at 90° contributes to this. However, in the sample that has not been subject to processing, the percentage elongation values of the raffia structure in the waft direction are lower (Figure 7). The highest value among the elongation values of raffia fabrics subjected to chemical operation is the value obtained by the application of 40% acetic acid. The reason for this is the ester bonds composed by the cellulosic structures of raffia fabric during acetylation.^49–51

Figure 6.

Weft direction (0°) percentage elongation values of raw raffia woven fabric and of raffia woven fabric subjected to chemical modification with different methods.

Figure 7.

Warp direction (90°) percentage elongation values of raw raffia woven fabric and of raffia woven fabric subjected to chemical modification with different methods.

Figures 8 and 9 show that the tensile strength values in both weft/warp directions of composites composed of raffia woven reinforcement fabric modified by different methods and different chemical materials and by matrix PES resin. Accordingly, an increase has been ensured in the tensile strength values of the composite reinforced by raffia fabric processed with microwaves. This is because microwave energy ensures more consistent heating on the material. In conventional heating methods, at first the external wall of the material heats up, and then as heating is towards the molecular center, the external topography of the material may be damaged in watery reaction environments. In fact, microwave energy ensures regular heating in a short period of time through penetrating at each point of the dissolvent sample within the reaction mixture. Considering microwave heating, the surface irregularity in chemical treatments performed based on conventional methods is disappears and this has positive effects on the material. While the lignin layer on the surface of raffia fabric and the hydrophility of its hemicellulose have decreased in the raffia fabric subjected to surface modification by the microwave energy method, the surface of the fiber has not been damaged.

Figure 8.

Warp direction (90°) tensile strength values of raw raffia woven fabric and of raffia woven fabric subjected to chemical modification with different methods/strength specifications of polyester resin-based composite.

Figure 9.

Weft direction (0°) tensile strength values of raw raffia woven fabric and of raffia woven fabric subjected to chemical modification with different methods/strength specifications of polyester resin-based composite.

The effect of ester bonds composed of acetylation has increased the tensile strength values of raffia fabric. It has been observed that a good adhesion has been ensured in between the matrix and fabric by the effect on the fibers of raffia fabric through the acetylation operation made by the microwave energy method. This is because heating during modification made by the microwave energy method is both short term and uniform on the molecules. It has been observed that close packing in between the cellulose chains of the internal structure of fibers due to the non-polar structures of lignin and hemicellulose within the internal structure of raffia fibers has decreased the hydrophility in between the matrix of the composite and raffia woven structure to a minimum and has increased the tensile strength values as well as improving the conformity.^52,53

In Figure 10, when the percentage elongation warp values of the composite are evaluated in respect of the difference between methods, it provides the highest elongation values by the microwave energy method. The elongation values of the raffia composite modified by the microwave energy method with 30% acetic acid are the highest elongation values. Acetylation has been effective on the hydroxyl groups in hemicellulose, and with the help of microwave energy, the elongation of the fiber without damage to the surface of the fiber has also been effective on the elongation values of the composite structure. Figure 11 proves that the elongation value is higher in the weft direction compared with the warp direction.

Figure 10.

Warp direction (90°) elongation values of raw raffia woven fabric and of raffia woven fabric subjected to chemical modification with different methods/strength specifications of polyester resin-based composite.

Figure 11.

Weft direction (0°) elongation values of raw raffia woven fabric and of raffia woven fabric subjected to chemical modification with different methods/strength specifications of polyester resin-based composite.

In general, the elongation values of composites composed of fabrics processed with organic acids are higher. In addition, the elongation values of reinforcement fabric composites modified by maleic anhydride are lower than the structures of untreated fiber structures. However, even if maleic anhydride has no positive effect on the elongation values of the reinforcement fabric composite, higher elongation values have been obtained by the microwave energy method than the conventional method.

Attenuated total reflectance characterization

In Figure 12, the values of the untreated raffia fabric obtained from the ATR-FT-IR device and of raffia fabric processed with different chemical materials by the microwave energy method at the region of 4000–1000 cm⁻¹ are shown. The vibrations at the regions of 3330 and 2950 cm⁻¹ are characteristic –OH and C–H bonds of raffia fabric. –OH groups are primary and secondary alcohol groups within cellulose, hemicellulose, lignin and carboxylic acid groups within extractives.⁵⁴ The peak values of untreated raffia fabric within this band range are less than the peak values of processed fibers. The reason for this is the separation of extractives and hemicellulose on the processed raffia-based fabric from the surface of the fiber. However, this decrease is not observed in the band range where the –OH groups of raffia fabric processed with acetic acid are available.⁵⁵ This condition can also be observed by the increase of –OH bonds and by the increase in tensile strength values (Figure 5 and 6). The 1737 cm⁻¹ band is the characteristic lignin and carbonyl groups in hemicellulose. In addition, the decrease of the band where the –CH groups are available emphasizes that the hemicellulose on the raffia fabric has been removed. The band value of fabric processed with acetic acid is lower compared with the non-processed fabrics or fabrics processed with other chemicals. Hemicellulose has been broken down after the deacetylation operation.⁵⁶ The decreases on the 1645 cm^–1 band are alpha keto carbonyl groups of –C=C bonds of fibers within the raffia fabric. The decrease in these bonds has contributed to the surface modification of raffia fabric.⁵⁷ The 1514 and 1480 cm⁻¹ band, and typical C=C bonds within the lignin, are rich carbonyl bonds composed by the dissolution of lignin hemicellulose of raffia-based fabric.⁵⁸ –CH ester bonds and C–O vibrations at 1362 and 1220 cm⁻¹ absorbance peaks have been composed by the dissolution of lignin after the acetylation operation on hydroxyl groups. Band values of raffia fabric modified by microwave operation and acetic acid are higher than the band values of samples that are not processed or processed with other chemical materials.⁵⁹

Figure 12.

Attenuated total reflectance-Fourier transform infrared characterization of raw and of raffia-based woven fabric by the microwave energy treatment with chemicals.

The ester bonds increasing during the acetylation operation and being effective on mechanical specifications are the things that contribute. Also the decrease in peaks in the 900–1000 cm⁻¹ band range has shown that the –OH bonds deformed at carbohydrates within the cellulose following the chemical operations of raffia fabric. When the weight loss rates of fabric processed with acetic acid are considered, the highest weight loss values have been obtained from the ones that are processed with acetic acid. It has been determined that the fabrics subjected to surface modification with acetic acid and by the microwave method have remove the highest hemicellulose, lignin and extractives; however, it has been determined that they have not been not been damaged significantly as the result of this operation.

Evaluation of the results of scanning electron microscopy analysis

In Figure 13(a), the surface topography of untreated raffia-based fabric has been showed. In Figure 13(b) the topography of the surface processed with maleic anhydride, in Figure 13(c) the topography of the surface processed with formic acid, in Figure 13(d) the topography of the surface processed with acetic acid are shown.

Figure 13.

Surface scanning electron microscopy views of untreated raffia fabric and fabric subjected to surface modification with different chemical materials using the microwave energy method: (a) untreated raffia-based fabric (I); (a) untreated raffia-based fabric (II); (b) raffia fabric microwave processed with maleic anhydride (15%) (I); (b) raffia fabric microwave processed with maleic anhydride (15%) (II); (c) raffia fabric microwave processed with formic acid 50% (I); (c) raffia fabric microwave processed with formic acid 50% (II); (d) raffia fabric microwave processed with acetic acid 40% (I); (d) raffia fabric microwave processed with acetic acid 40% (II).

While the porosity of surfaces processed with maleic anhydride was more than the untreated sample, it is less than that of the fabric processed with formic acid and acetic acid. When surfaces processed with acetic acid are considered, it is observed that it is rougher than surface modification with formic acid. By the acetic acid operation, the extractives, hemicellulose and lignin on the surface have been removed. When the morphologies of the untreated surface and the surface processed with acetic acid are compared, as the result of esterification realized by the acetic acid operation, the hydroxyl groups on the surface have been replaced by acetyl groups, and it has been observed that it showed cleaning by composing better roughness on the surface.^60–63

In Figure 14(a), the surface topography of the untreated raffia fabric/PES composite is shown. In Figure 14(b), the surface of the raffia fabric/PES composite has been processed with maleic anhydride; in Figure 14(c), the surface of the raffia fabric/PES composite has been processed with formic acid; in Figure 14(d), the morphologies of surfaces of the raffia fabric/PES composite processed with acetic acid are shown.

Figure 14.

Surface scanning electron microscopy views of untreated raffia woven fabric/polyester (PES) resin composite and raffia woven fabric/PES resin composite processed with different chemical materials using the microwave energy method: (a) untreated raffia fabric/PES composite (I); (a) untreated raffia fabric/PES composite (II); (b) raffia fabric with maleic anhydride microwave processed/PES composite (15%) (I); (b) raffia fabric with maleic anhydride microwave processed/PES composite (15%) (II); (c) raffia fabric with formic acid microwave processed/PES composite (50%) (I); (c) raffia fabric with formic acid microwave processed/PES composite (50%) (II); (d) raffia fabric with acetic acid microwave processed/PES composite (40%) (I); (d) raffia fabric with acetic acid microwave processed/PES composite (40%) (II).

In Figure 14(a), when the appearance of the composite composed of untreated raffia fabric and PES resin is examined, it is a reality that a porous structure has composed in between the raffia surface and the matrix and no complete adhesion has been obtained. It is observed in Figures 14(b), (c) and (d) that a higher adhesion occurs in between the surface of the raffia fabric – subjected to surface modification with maleic anhydride, formic acid and acetic acid by microwave energy method – and matrix. However, as understood from the best surface topography, the best adherence is the surface processed with acetic acid. Acetic acid operation by the microwave method has increased the interaction in between the surface of the fiber and the matrix. PES resin used as a matrix has better penetrated to the surface. Thus, an interlocking has occurred in between the surface and matrix.

Conclusions

Surfaces of raffia-based woven fabric have been modified with three different chemical materials of different concentrations by the conventional method and the microwave energy method. In general, the microwave energy method has been more successful than the conventional method. It has been observed that concentrations of chemical materials were effective on modification. In surface modifications made with 40% acetic acid in the microwave method, the best values have been obtained in respect of tensile strength, elongation and weight loss. By the acetylation operation, the hydroxyl groups on the surface of raffia-based woven fabric have been replaced by the acetyl groups and have ensured an effective cleaning on the surface, and the surface of the fiber has not been damaged by the assistance of ester bonds; it can be concluded that having better mechanical specifications than the surface modifications made with other chemical materials can be linked to this reason. The internal structures of the molecules have been affected with the modification operation made by the microwave energy method without damaging the surface, and time saving has been obtained by performing the operation in a short time. This study has revealed that the microwave energy method is an ecological alternative method to be used in the modification of fibers, fabrics and similar surfaces.

Footnotes

Funding

This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

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