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Study of the interfacial properties of natural fibre reinforced polyethylene
Polymer Testing 24 (2005) 694–698 www.elsevier.com/locate/polytest
Test Method
Study of the interfacial properties of natural fibre reinforced polyethylene F.G. Torres*, M.L. Cubillas Department of Mechanical Engineering, Polymers and Composites Group-POLYCOM, Catholic University of Peru, Av. Universitaria Cdra. 18. s/n, Lima 32, Peru Received 7 April 2005; accepted 12 May 2005
Abstract In the present paper, the interfacial properties of extruded and compression moulded natural fibre reinforced thermoplastics (NFRTP) are studied. The interfacial shear strength of PE-sisal composites was measured using the single fibre fragmentation test (SFFT). The difficulties in obtaining significant measurements are discussed and assessed. The main problems found were the non-transparent nature of the matrix, the irregular shape of the fibres, and the variability in fibre–matrix adhesion encountered even in single fibre specimens. Scanning Electron Microscope (SEM) pictures obtained from fractured surfaces were used for a qualitative evaluation of the interfacial properties of NFRTPs. Fibre treatment with stearic acid increased the interfacial shear strength by 23% with respect to untreated fibres. The improvements in interfacial shear strength found for the treated specimens were consistent with observations from SEM fractographs. q 2005 Elsevier Ltd. All rights reserved. Keywords: Interfacial properties; Single fibre fragmentation test; Natural fibre composites
1. Introduction Natural fibre composites have found an increasing number of applications in recent years [1–9]. Car manufacturers have shown special interest in these materials for the replacement of glass fibre reinforced panels. The advantages of natural fibres over their traditional counterparts include: relatively low cost, low weight, less damage to processing equipment, improved surface finish of moulded parts (compared to glass fibre composites), good relative mechanical properties. Another important advantage of natural fibres is that they are relatively abundant in nature and, therefore, can be obtained from renewable resources. They can also be recycled. The main disadvantages of natural fibres are: their low permissible processing
* Corresponding author. E-mail address: [email protected] (F.G. Torres).
0142-9418/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2005.05.004
temperatures, their tendency to form clumps, and their hydrophilic nature [4–6]. Experimental data of their mechanical properties, particularly when tested under different processing conditions, have shown inconsistent values in many cases [1–3]. The irregular characteristics of natural fibres are one of the main reasons for this. On the other hand, natural fibres are hydrophilic and many thermoplastics are hydrophobic. This leads, in many cases, to problems associated with the interfacial properties of this type of composite [1–3]. Various treatments are used to improve the matrix-fibre adhesion in natural fibre reinforced composites. Currently, this step is considered critical in the development of these materials. The methods for surface modification can be physical or chemical according to the way they modify the fibre surface. Other frequently used treatments are bleaching, acetylation and alkali treatment. The main chemical method used in the surface modification of natural fibres is chemical coupling [7]. The coupling agent is chosen to form
F.G. Torres, M.L. Cubillas / Polymer Testing 24 (2005) 694–698
chemical bonds between the cellulose in the fibre and the polymer matrix [8]. Other chemical methods involve changing the surface tension and impregnating the fibres [9]. The change in surface tension is related to the hydrophobicity of the fibre. The use of stearic acid that hydrophobizes the fibres and improves their dispersion [6,9] is an example. In this paper, the interfacial properties of sisal reinforced polyethylene composites are assessed by means of the single fibre fragmentation test. The results are compared with qualitative data from morphological characterization tests.
2. Single fibre fragmentation test The single fibre fragmentation test has been used in the past for the measurement of the interfacial shear strength of polymer fibre composites [10–14]. It can be carried out by applying a sustained tensile load to a specimen with an embedded single fibre. The number and length of the fragments produced were monitored and quantified. For the data analysis, when using the SFFT, the average interfacial shear strength can be calculated with the following equation [15].: df 1 tc Z k sc (1) 2 lc
695
e = 1 mm Fig. 1. Specimen geometry for the single fibre fragmentation tests.
3.3. Fibre treatment All fibres were pre-washed in a solution consisting of water and 3% non-ionic detergent for 1 h at 70 8C followed by washing with distilled water and air drying in an oven for 24 h at 65 8C. The fibres were then treated with 3% of stearic acid. Previous work from this laboratory indicates that this concentration seems to be enough in order to achieve a considerable reduction in the size and number of fibre clumps and agglomerates during standard processing operations [1–3,16]. 3.4. Samples preparation Dumb-bell specimens (Fig. 1) were prepared by compression moulding. Processing conditions were 130 8C/15 min. The fibres had to be placed accurately within the dumb-bell by means of special centring devices attached to the mould. 3.5. Characterisation of matrix and fibres
where: t interfacial shear strength between fibre and matrix sc fibre tensile strength (MPa) df fibre mean diameter l average fragment length k statistical correction factor (kZ0.889) [15].
3. Experimental 3.1. Materials The specimens for the SFFT were prepared from polyethylene powder with a melt index of 2.5 (190C/2. 16 kg) and sisal fibres as reinforcement. Untreated, as well as pre-treated fibres (with stearic acid), were used. Stearic acid was used, since it has been found to reduce the presence of processing defects in final products [2].
The tensile strength of the matrix was assessed according to ISO 527. Fibre tensile properties were determined according to ASTM D2256 [17,18] 3.6. Single fibre fragmentation tests A Columbine tensile testing machine for plastics with a 2.5 KN load cell was used for the experiments. An additional lighting device was used to increase visibility of the fibres in the opaque polyethylene matrices. A crosshead speed of 4 mm/min was used in the experiments. The scheme of the rig used for SFFT experiments is shown in Fig. 2.
fixed clamp Sample
travelling macroscope fitted with digital camera moving clamp
3.2. Measurement of fibre diameter Fibre diameter was measured using a profile magnifier at 50!. Five measurements were taken at different cross sections in each fibre and an average diameter was estimated.
light source
Fig. 2. Disposition used for the SFFT.
test direction
696
F.G. Torres, M.L. Cubillas / Polymer Testing 24 (2005) 694–698
Table 1 Average diameter of sisal fibres
Table 3 Tensile strength of sisal fibres
Property
(mm)
Average diameter Standard deviation Max. value Min. value
223.53 49.62 375 122
Tensile strength values (MPa) Avg. tensile strength Standard deviation Max. value Min. value
3.7. Morphological characterization
234.30 75.10 320.50 125.80
400
Measurements (µm)
350
Microscopy studies included the use of scanning electron microscopy (SEM) and stereomicroscopy. Fracture surfaces of SFFT specimens were studied using an RJ Lee SEM, using voltages in the range10–20 kV. Specimens were gold coated as described in a previous report from this laboratory. [1]
300 250 200 150 100 50 0 0
4. Results and discussion
5
10
15
20
25
30
35
40
Number of samples taken Fig. 3. Scatter graph of sisal fibre diameter.
4.1. Measurement of fibre diameter Table 1 shows the measurements obtained for the diameter of the fibres studied. It is clear from the data that there is an important variation in fibre diameter among sisal fibres of the same batch. The high standard deviation encountered indicates lack of consistency in the geometry of natural fibres. 4.2. Tensile strength of matrix and fibre It is clear from Tables 2 and 3, that the variation in tensile strength is much higher for sisal fibres than for the polymeric matrix (10% in the first case and 32% in the second). The high variation in tensile strength among sisal fibres is clearly an important source of error in the calculation of the interfacial shear strength. Sisal fibres, like many other natural fibres, differ not only geometrically (see Fig. 3 and Table 1) but also morphologically, depending on how the individual fibrils are organised in the fibre. This certainly affects tensile strength in this type of fibre. Fig. 3. shows a scatter graph with different diameter measurements of sisal fibres.
4.3. Single fibre fragmentation tests Using Eq. (1), it is possible to calculate the interfacial shear strength for the specimens with and without fibre treatment. The results obtained in this work are in the same order of magnitude compared to data available in the literature for polyester sisal-systems [18]. It is clear from Table 4, that fibre pre-treatment with stearic acid improves the interfacial shear strength (23%) with respect to untreated fibres. These results need to be treated carefully, partly due to the fact that adhesion is variable along the fibre-matrix interface. Other reasons for the variability in the results may include experimental errors due to the opacity of the PE matrix and the irregular surfaces and cross sections of the natural fibres. The issue of results reproducibility in the SFFT, when dealing with fibres of differing surface structure, has been discussed by Gorbatkina [19]. That author considers that standard deviations in the interfacial shear strength (t) in the range (5–15%) indicate ‘good reproducibility’.
Table 4 Interfacial shear strength t in MPa for sisal fibre reinforced polyethylene composites
Table 2 Tensile strength of PE matrix Tensile strength values (MPa) Avg. tensile strength Standard deviation Max. value Min. value
11.30 1.20 12.30 9.82
Average Std. dev. Max. value Min. value
No treatment
Pre-treated fibres
2.16 0.42 2.68 1.51
2.66 0.58 3.58 2.14
F.G. Torres, M.L. Cubillas / Polymer Testing 24 (2005) 694–698
697
Fig. 4. Typical fracture surface of PE-sisal SFFT specimen for an untreated fibre.
4.4. Morphological characterization Figs. 4 and 5 show typical fracture surfaces of PE-sisal SFFT specimens, which were loaded until fracture was achieved. Fig. 4 corresponds to an untreated PE-sisal specimen, while Fig. 5 was taken from a treated specimen. In all cases, a relatively ductile failure can be observed in the matrix region adjacent to the fibres. Fig. 4 shows a relatively large fibre pull-out compared with Fig. 5 (a), where virtually no pull-out can be observed. This indicates higher interfacial shear strength for the treated specimens (see Fig. 5 (a) and (b)). Fracture of individual fibrils can be observed in Fig. 5 (a) and (b). Fig. 5. (a) Typical fracture surface of PE-sisal SFFT specimen for a treated fibre (b) Detail of Fig. 5 (a). Fracture surface of PE-sisal SFFT specimen showing individual fibrils.
5. Conclusions The single fibre fragmentation test can provide comparative results for the interfacial shear strength t of natural fibre reinforced polymers. In this work, relatively low values for t were obtained (in the range 1.5–3.5 MPa). Pre-treated fibres showed improved values (23%) for t compared to untreated fibres. The variability of the results was relatively high as indicated by a high standard deviation (21%). Experimental errors (due to the opacity of the matrix), as well as the inherent characteristics of the fibres and the fibre–matrix interface, might be the causes for such variability. Qualitative improvements in interfacial shear strength for the treated specimens with respect to the untreated ones were confirmed with observations from SEM fractographs.
Acknowledgements Financial aid received from the Department of Engineering and the Directorate of Research (DAI) of the PUCP is gratefully acknowledged.
References [1] F.G. Torres, R.M. Diaz, Morphological characterisation of natural fibre reinforced thermoplastics (NFRTP) processed by extrusion, compression and rotational moulding, Polymers and Polymer Composites 12 (8) (2004) 705–718. [2] F.G. Torres, M. Aguirre, Rotational moulding and powder processing of natural fibre reinforced thermoplastics, International Polymer Processing 18 (2) (2003) 204–210.
698
F.G. Torres, M.L. Cubillas / Polymer Testing 24 (2005) 694–698
[3] F.G. Torres, B. Ochoa, E. Machicao, Single screw extrusion of natural fibre reinforced thermoplastics (NFRTP), International Polymer Processing 18 (1) (2003) 33–40. [4] A.K. Mohanty, M. Misra, G. Hinrichsen, Biofibers, biodegradable polymers and biocomposites: an overview, Macromolecular Materials and Engineering 276–277 (2000) 1–24. [5] D. Nabi Saheb, J.P. Jog, Natural fiber polymer composites: a review, Advances in Polymer Technology 18 (1999) 351. [6] R.M. Rowell, A.R. Sanadi, D.F. Caulfield, R.E. Jacobson, Proceedings of First International Lignocellulosics-Plastics Composites, Sa˜o Paulo, Brazil 1996 p. 23. [7] J. Gassan, A.K. Bledzki, Possibilities to improve the properties of natural fiber reinforced plastics by fiber modification - jute polypropylene, Applied Composite Materials 7 (2000) 373. [8] J. Gassan, A.K. Bledzki, The influence of fiber-surface treatment on the mechanical properties of jute-polypropylene composites, Composites Part A 28A (12) (1997) 1001. [9] A.K. Bledzki, J.M. Gassan, Composites reinforced with cellulose based fibres, Progress in Polymer Science 24 (1999) 221–274. [10] M.J. Lodeiro, Investigation of PMC Interface Properties Using the Single-Fibre Fragmentation Technique, NPL Report MATC(A)16, 2001. [11] M.J. Lodeiro, Single-Fibre Fragmentation Test for the Characterisation of Interfacial Phenomena in PMCs, NPL Measurement Note MATC(MN)07, 2001.
[12] D.A. Mendels, Analysis of the Single-Fibre Fragmentation Test, NPL Report MATC(A)17, 2001. [13] A.N. Netravali, R.B. Henstenburg, S.L. Phoenix, P. Schwartz, Interfacial shear strength studies using the single-filament composite test I: experiments on graphite fibers in epoxy, Polymer Composites 10 (1989) 226–241. [14] J. George, M.S. Sreekala, S. Thomas, A review on interface modification and characterisation of natural fibre plastic composites, Polymer Engineering and Science 41 (9) (2001) 1471–1485. [15] P. Herrera-Franco, L.T. Drzal, Comparison of methods for the measurement of fiber-matrix adhesion in composites, Composites 23 (1992) 2–27. [16] C. Grande, F.G. Torres, Investigation of fibre organisation and degradation in single screw extrusion of natural fibre reinforced thermoplastics, Advances in Polymer Technology 24 (2) (2005). [17] ASTM 2256 Standard Test Method for Tensile Properties of Yarns by the Single-Strand Method, 2002. [18] T.H.D. Sydenstricker, S. Mochnaz, S.C. Amico, Pull-out and other evaluations in sisal reinforced polyester biocomposites, Polymer Testing 22 (2003) 375–380. [19] Yu.A. Gorbatkina, Adhesive Strength of Fibre-Polymer Systems, Ellis Horwood Ltd, Chinchester, 1992.
Test Method
Study of the interfacial properties of natural fibre reinforced polyethylene F.G. Torres*, M.L. Cubillas Department of Mechanical Engineering, Polymers and Composites Group-POLYCOM, Catholic University of Peru, Av. Universitaria Cdra. 18. s/n, Lima 32, Peru Received 7 April 2005; accepted 12 May 2005
Abstract In the present paper, the interfacial properties of extruded and compression moulded natural fibre reinforced thermoplastics (NFRTP) are studied. The interfacial shear strength of PE-sisal composites was measured using the single fibre fragmentation test (SFFT). The difficulties in obtaining significant measurements are discussed and assessed. The main problems found were the non-transparent nature of the matrix, the irregular shape of the fibres, and the variability in fibre–matrix adhesion encountered even in single fibre specimens. Scanning Electron Microscope (SEM) pictures obtained from fractured surfaces were used for a qualitative evaluation of the interfacial properties of NFRTPs. Fibre treatment with stearic acid increased the interfacial shear strength by 23% with respect to untreated fibres. The improvements in interfacial shear strength found for the treated specimens were consistent with observations from SEM fractographs. q 2005 Elsevier Ltd. All rights reserved. Keywords: Interfacial properties; Single fibre fragmentation test; Natural fibre composites
1. Introduction Natural fibre composites have found an increasing number of applications in recent years [1–9]. Car manufacturers have shown special interest in these materials for the replacement of glass fibre reinforced panels. The advantages of natural fibres over their traditional counterparts include: relatively low cost, low weight, less damage to processing equipment, improved surface finish of moulded parts (compared to glass fibre composites), good relative mechanical properties. Another important advantage of natural fibres is that they are relatively abundant in nature and, therefore, can be obtained from renewable resources. They can also be recycled. The main disadvantages of natural fibres are: their low permissible processing
* Corresponding author. E-mail address: [email protected] (F.G. Torres).
0142-9418/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2005.05.004
temperatures, their tendency to form clumps, and their hydrophilic nature [4–6]. Experimental data of their mechanical properties, particularly when tested under different processing conditions, have shown inconsistent values in many cases [1–3]. The irregular characteristics of natural fibres are one of the main reasons for this. On the other hand, natural fibres are hydrophilic and many thermoplastics are hydrophobic. This leads, in many cases, to problems associated with the interfacial properties of this type of composite [1–3]. Various treatments are used to improve the matrix-fibre adhesion in natural fibre reinforced composites. Currently, this step is considered critical in the development of these materials. The methods for surface modification can be physical or chemical according to the way they modify the fibre surface. Other frequently used treatments are bleaching, acetylation and alkali treatment. The main chemical method used in the surface modification of natural fibres is chemical coupling [7]. The coupling agent is chosen to form
F.G. Torres, M.L. Cubillas / Polymer Testing 24 (2005) 694–698
chemical bonds between the cellulose in the fibre and the polymer matrix [8]. Other chemical methods involve changing the surface tension and impregnating the fibres [9]. The change in surface tension is related to the hydrophobicity of the fibre. The use of stearic acid that hydrophobizes the fibres and improves their dispersion [6,9] is an example. In this paper, the interfacial properties of sisal reinforced polyethylene composites are assessed by means of the single fibre fragmentation test. The results are compared with qualitative data from morphological characterization tests.
2. Single fibre fragmentation test The single fibre fragmentation test has been used in the past for the measurement of the interfacial shear strength of polymer fibre composites [10–14]. It can be carried out by applying a sustained tensile load to a specimen with an embedded single fibre. The number and length of the fragments produced were monitored and quantified. For the data analysis, when using the SFFT, the average interfacial shear strength can be calculated with the following equation [15].: df 1 tc Z k sc (1) 2 lc
695
e = 1 mm Fig. 1. Specimen geometry for the single fibre fragmentation tests.
3.3. Fibre treatment All fibres were pre-washed in a solution consisting of water and 3% non-ionic detergent for 1 h at 70 8C followed by washing with distilled water and air drying in an oven for 24 h at 65 8C. The fibres were then treated with 3% of stearic acid. Previous work from this laboratory indicates that this concentration seems to be enough in order to achieve a considerable reduction in the size and number of fibre clumps and agglomerates during standard processing operations [1–3,16]. 3.4. Samples preparation Dumb-bell specimens (Fig. 1) were prepared by compression moulding. Processing conditions were 130 8C/15 min. The fibres had to be placed accurately within the dumb-bell by means of special centring devices attached to the mould. 3.5. Characterisation of matrix and fibres
where: t interfacial shear strength between fibre and matrix sc fibre tensile strength (MPa) df fibre mean diameter l average fragment length k statistical correction factor (kZ0.889) [15].
3. Experimental 3.1. Materials The specimens for the SFFT were prepared from polyethylene powder with a melt index of 2.5 (190C/2. 16 kg) and sisal fibres as reinforcement. Untreated, as well as pre-treated fibres (with stearic acid), were used. Stearic acid was used, since it has been found to reduce the presence of processing defects in final products [2].
The tensile strength of the matrix was assessed according to ISO 527. Fibre tensile properties were determined according to ASTM D2256 [17,18] 3.6. Single fibre fragmentation tests A Columbine tensile testing machine for plastics with a 2.5 KN load cell was used for the experiments. An additional lighting device was used to increase visibility of the fibres in the opaque polyethylene matrices. A crosshead speed of 4 mm/min was used in the experiments. The scheme of the rig used for SFFT experiments is shown in Fig. 2.
fixed clamp Sample
travelling macroscope fitted with digital camera moving clamp
3.2. Measurement of fibre diameter Fibre diameter was measured using a profile magnifier at 50!. Five measurements were taken at different cross sections in each fibre and an average diameter was estimated.
light source
Fig. 2. Disposition used for the SFFT.
test direction
696
F.G. Torres, M.L. Cubillas / Polymer Testing 24 (2005) 694–698
Table 1 Average diameter of sisal fibres
Table 3 Tensile strength of sisal fibres
Property
(mm)
Average diameter Standard deviation Max. value Min. value
223.53 49.62 375 122
Tensile strength values (MPa) Avg. tensile strength Standard deviation Max. value Min. value
3.7. Morphological characterization
234.30 75.10 320.50 125.80
400
Measurements (µm)
350
Microscopy studies included the use of scanning electron microscopy (SEM) and stereomicroscopy. Fracture surfaces of SFFT specimens were studied using an RJ Lee SEM, using voltages in the range10–20 kV. Specimens were gold coated as described in a previous report from this laboratory. [1]
300 250 200 150 100 50 0 0
4. Results and discussion
5
10
15
20
25
30
35
40
Number of samples taken Fig. 3. Scatter graph of sisal fibre diameter.
4.1. Measurement of fibre diameter Table 1 shows the measurements obtained for the diameter of the fibres studied. It is clear from the data that there is an important variation in fibre diameter among sisal fibres of the same batch. The high standard deviation encountered indicates lack of consistency in the geometry of natural fibres. 4.2. Tensile strength of matrix and fibre It is clear from Tables 2 and 3, that the variation in tensile strength is much higher for sisal fibres than for the polymeric matrix (10% in the first case and 32% in the second). The high variation in tensile strength among sisal fibres is clearly an important source of error in the calculation of the interfacial shear strength. Sisal fibres, like many other natural fibres, differ not only geometrically (see Fig. 3 and Table 1) but also morphologically, depending on how the individual fibrils are organised in the fibre. This certainly affects tensile strength in this type of fibre. Fig. 3. shows a scatter graph with different diameter measurements of sisal fibres.
4.3. Single fibre fragmentation tests Using Eq. (1), it is possible to calculate the interfacial shear strength for the specimens with and without fibre treatment. The results obtained in this work are in the same order of magnitude compared to data available in the literature for polyester sisal-systems [18]. It is clear from Table 4, that fibre pre-treatment with stearic acid improves the interfacial shear strength (23%) with respect to untreated fibres. These results need to be treated carefully, partly due to the fact that adhesion is variable along the fibre-matrix interface. Other reasons for the variability in the results may include experimental errors due to the opacity of the PE matrix and the irregular surfaces and cross sections of the natural fibres. The issue of results reproducibility in the SFFT, when dealing with fibres of differing surface structure, has been discussed by Gorbatkina [19]. That author considers that standard deviations in the interfacial shear strength (t) in the range (5–15%) indicate ‘good reproducibility’.
Table 4 Interfacial shear strength t in MPa for sisal fibre reinforced polyethylene composites
Table 2 Tensile strength of PE matrix Tensile strength values (MPa) Avg. tensile strength Standard deviation Max. value Min. value
11.30 1.20 12.30 9.82
Average Std. dev. Max. value Min. value
No treatment
Pre-treated fibres
2.16 0.42 2.68 1.51
2.66 0.58 3.58 2.14
F.G. Torres, M.L. Cubillas / Polymer Testing 24 (2005) 694–698
697
Fig. 4. Typical fracture surface of PE-sisal SFFT specimen for an untreated fibre.
4.4. Morphological characterization Figs. 4 and 5 show typical fracture surfaces of PE-sisal SFFT specimens, which were loaded until fracture was achieved. Fig. 4 corresponds to an untreated PE-sisal specimen, while Fig. 5 was taken from a treated specimen. In all cases, a relatively ductile failure can be observed in the matrix region adjacent to the fibres. Fig. 4 shows a relatively large fibre pull-out compared with Fig. 5 (a), where virtually no pull-out can be observed. This indicates higher interfacial shear strength for the treated specimens (see Fig. 5 (a) and (b)). Fracture of individual fibrils can be observed in Fig. 5 (a) and (b). Fig. 5. (a) Typical fracture surface of PE-sisal SFFT specimen for a treated fibre (b) Detail of Fig. 5 (a). Fracture surface of PE-sisal SFFT specimen showing individual fibrils.
5. Conclusions The single fibre fragmentation test can provide comparative results for the interfacial shear strength t of natural fibre reinforced polymers. In this work, relatively low values for t were obtained (in the range 1.5–3.5 MPa). Pre-treated fibres showed improved values (23%) for t compared to untreated fibres. The variability of the results was relatively high as indicated by a high standard deviation (21%). Experimental errors (due to the opacity of the matrix), as well as the inherent characteristics of the fibres and the fibre–matrix interface, might be the causes for such variability. Qualitative improvements in interfacial shear strength for the treated specimens with respect to the untreated ones were confirmed with observations from SEM fractographs.
Acknowledgements Financial aid received from the Department of Engineering and the Directorate of Research (DAI) of the PUCP is gratefully acknowledged.
References [1] F.G. Torres, R.M. Diaz, Morphological characterisation of natural fibre reinforced thermoplastics (NFRTP) processed by extrusion, compression and rotational moulding, Polymers and Polymer Composites 12 (8) (2004) 705–718. [2] F.G. Torres, M. Aguirre, Rotational moulding and powder processing of natural fibre reinforced thermoplastics, International Polymer Processing 18 (2) (2003) 204–210.
698
F.G. Torres, M.L. Cubillas / Polymer Testing 24 (2005) 694–698
[3] F.G. Torres, B. Ochoa, E. Machicao, Single screw extrusion of natural fibre reinforced thermoplastics (NFRTP), International Polymer Processing 18 (1) (2003) 33–40. [4] A.K. Mohanty, M. Misra, G. Hinrichsen, Biofibers, biodegradable polymers and biocomposites: an overview, Macromolecular Materials and Engineering 276–277 (2000) 1–24. [5] D. Nabi Saheb, J.P. Jog, Natural fiber polymer composites: a review, Advances in Polymer Technology 18 (1999) 351. [6] R.M. Rowell, A.R. Sanadi, D.F. Caulfield, R.E. Jacobson, Proceedings of First International Lignocellulosics-Plastics Composites, Sa˜o Paulo, Brazil 1996 p. 23. [7] J. Gassan, A.K. Bledzki, Possibilities to improve the properties of natural fiber reinforced plastics by fiber modification - jute polypropylene, Applied Composite Materials 7 (2000) 373. [8] J. Gassan, A.K. Bledzki, The influence of fiber-surface treatment on the mechanical properties of jute-polypropylene composites, Composites Part A 28A (12) (1997) 1001. [9] A.K. Bledzki, J.M. Gassan, Composites reinforced with cellulose based fibres, Progress in Polymer Science 24 (1999) 221–274. [10] M.J. Lodeiro, Investigation of PMC Interface Properties Using the Single-Fibre Fragmentation Technique, NPL Report MATC(A)16, 2001. [11] M.J. Lodeiro, Single-Fibre Fragmentation Test for the Characterisation of Interfacial Phenomena in PMCs, NPL Measurement Note MATC(MN)07, 2001.
[12] D.A. Mendels, Analysis of the Single-Fibre Fragmentation Test, NPL Report MATC(A)17, 2001. [13] A.N. Netravali, R.B. Henstenburg, S.L. Phoenix, P. Schwartz, Interfacial shear strength studies using the single-filament composite test I: experiments on graphite fibers in epoxy, Polymer Composites 10 (1989) 226–241. [14] J. George, M.S. Sreekala, S. Thomas, A review on interface modification and characterisation of natural fibre plastic composites, Polymer Engineering and Science 41 (9) (2001) 1471–1485. [15] P. Herrera-Franco, L.T. Drzal, Comparison of methods for the measurement of fiber-matrix adhesion in composites, Composites 23 (1992) 2–27. [16] C. Grande, F.G. Torres, Investigation of fibre organisation and degradation in single screw extrusion of natural fibre reinforced thermoplastics, Advances in Polymer Technology 24 (2) (2005). [17] ASTM 2256 Standard Test Method for Tensile Properties of Yarns by the Single-Strand Method, 2002. [18] T.H.D. Sydenstricker, S. Mochnaz, S.C. Amico, Pull-out and other evaluations in sisal reinforced polyester biocomposites, Polymer Testing 22 (2003) 375–380. [19] Yu.A. Gorbatkina, Adhesive Strength of Fibre-Polymer Systems, Ellis Horwood Ltd, Chinchester, 1992.