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New biodegradable material based on RF plasma modified starch
Surface & Coatings Technology 200 (2005) 539 – 543 www.elsevier.com/locate/surfcoat
New biodegradable material based on RF plasma modified starch Hieronim Szymanowskia,*, Mariusz Kaczmareka, Maciej Gazicki-Lipmana, Leszek Klimeka, Bogusaaw Woz´niakb a
Institute for Materials Science and Engineering, Technical University of ‘o´dz´, ‘o´dz´, Poland b Leather Research Institute, ‘o´dz´, Poland Available online 25 May 2005
Abstract The work presents an application of potato starch as a filler for a composite material with high density polyethylene. It was assumed that, in order to improve miscibility of starch with polyethylene matrix, its surface should be made hydrophobic. Therefore, radio frequency (RF) plasma rotary reactor was applied to the surface modification of grains of starch. The plasma reactor was a capacitively coupled RF system equipped with external electrodes. Methane (CH4) was used as working medium. Measurements of a height of water capillary rise were applied to assess the hydrophilic properties of the grain surface. Starch, when modified with methane RF glow discharge, possessed considerably altered surface properties. It was substantially more hydrophobic—the modification process was able to lower capillary rise effect several times. Starch, modified in such a way, was used to prepare composite materials with polyethylene. Tensile strength and elongation at break of the composites were measured. The measurements showed a substantial improvement of mechanical properties of polyethylene samples filled with modified starch, compared to those filled with unmodified starch. Other techniques, such as Scanning Electron Microscopy (SEM) and Differential Scanning Calorimetry (DSC) were also used to characterize the composites. The results of the latter suggest that it was the deagglomeration effects of starch grains resulting in an enhancement of filler dispersion, rather than matrix – filler interaction, that was primarily responsible for the improvement of mechanical properties. D 2005 Elsevier B.V. All rights reserved. Keywords: Potato starch; Plasma processing; Hydrophilicity; Polyethylene; Composite
1. Introduction Polymer wastes constitute today a large ecological problem. Their substantial fraction is comprised of disposable packaging materials of very long composting times, counted in year-hundreds. Under these circumstances, a search for materials of better biodegradability is underway. One of the possible approaches concerns a use of composite systems. In such systems, biodegradable fillers, such as starch, can be used to fill a matrix made of typical thermoplastic polymers, such as polyethylene or polypropylene [1]. There is, however, one major problem with these composites. A polyolefine, with a very low polar component of its surface energy, does not sufficiently wet the surface of starch grains, characterized with a relatively high polar component. An * Corresponding author. Tel.: +48 42 631 22 81; fax: +48 42 636 67 90. E-mail address: [email protected] (H. Szymanowski). 0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.02.213
obvious solution is a minimization of the surface energy of the interface polymer/starch [2]. One way to realize this process is to lower the polar component of surface energy of starch. Low temperature plasma processes have been long used to modify polymer surfaces [3 –6]. A difficulty with the modification of a material used as a filler is its high surface to volume ratio. In other words, the modification of starch requires a plasma system able to work with substrates in a highly particulate form. Fluidal bed plasma reactor is one possibility [7,8]. A system, where the powdered substrate is set in motion, either vibration or rotation, constitutes an alternative solution. 2. Experimental The reactor was equipped with a set of external electrodes, to which the RF power was supplied from the
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H. Szymanowski et al. / Surface & Coatings Technology 200 (2005) 539 – 543
Fig. 1. Schematic representation of a rotating RF plasma reactor (a), the reactor at work (b).
Plasma Products RF5S power generator through a selfdesigned matching circuit. Methane (CH4) was used as working medium and its flow rate was controlled with the help of a MKS 1179 AX mass flow controller. A starch modification cycle began with setting the flow of CH4, then the rotation of the tubular element with a selected RPM value was introduced, and finally RF glow discharge was generated in the reactor. Powdered starch contained in this reactor was stirred very efficiently, thus enabling an effective plasma surface modification of the grains. The main aim of the modification process was surface hydrophobization of starch, i.e. a substantial decrease of its water contact angle. Therefore, an assessment of the process efficiency comprised measurements of capillary rise of water in glass tubes (1.8 mm in diameter) filled with starch. Methane plasma modified starch was used as a filler to fabricate composite materials with low density polyethylene (LDPE). They were made with the help of a Brabender, model PLP 651, extruder using temperature range of 135– 155 -C and the rate of the screw rotation of 20 RPM. Composites with unmodified starch were also produced for the sake of reference. Extruded materials were then pressed to form foils of a thickness of 0.8 mm, using Nike Eskilstuna press and pressing initial temperature of 180 -C. Tensile tests of the composites were performed with the
help of Instron 5566 tensile testing machine. The size of the specimens has been 4 50 mm. Scanning Electron Microscope (SEM) imaging of starch particles, as well as of the cross-sections of polyethylene/ starch composite materials, was carried out using a Hitachi F 3000 N scanning electron microscope. In order to assure their electrical conductivity the samples were deposited, by means of vacuum evaporation, with a thin film of metallic gold. Differential Scanning Calorimetry (DSC) of the samples was performed using a DSC2920 unit, manufactured by TA Instruments. Both, heating and cooling runs were performed between 150 and 150 -C, with the rate of 10 -C/min.
3. Results 3.1. Hydrophobization of starch Potato starch is considered a hydrophilic material. In our experiments, comprising water capillary rise, the maximum water elevation measured for native starch amounted to approximately 60 mm. Surface modification of starch grains with methane plasma made them substantially more hydrophobic. Fig. 2 presents the results of water capillary elevation for starch modified with methane plasma at the
Fig. 2. Results of capillary elevation measurements for starch modified with methane plasma at the flow rate of 6 sccm (a), at the flow rate of 2 sccm (b).
H. Szymanowski et al. / Surface & Coatings Technology 200 (2005) 539 – 543
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Fig. 3. SEM micrographs of starch grains: unmodified (a), and modified with methane plasma at different RF power values: 20 W (b), 40 W (c), 100 W (d). Flow rate of methane equals 6 sccm.
flow rate of methane equal 6 sccm (2a) and 2 sccm (2b), and at different values of RF power. It is apparent that modification of starch with methane plasma considerably decreases the maximum of water capillary elevation. This is an evidence of hydrophobization of starch grains, taking place in the modification process. SEM micrographs of pure starch filler, both unmodified and methane plasma modified, are presented in Fig. 3. Fig. 3a presents a collection of the unmodified starch grains. As seen in the micrograph, the grains exhibit a tendency towards agglomeration. They form a threedimensional cluster, with some of the particles being located backwards with respect to the others. As indicated by Fig. 3b, c and d, methane plasma modification reduces this tendency and the result depends on RF power input. While the grains modified at 20 W of RF power (Fig. 3b) still appear to form a 3-D cluster, those deposited at higher RF power input apparently form a single-particlethick layer. In addition, starch grains modified with methane plasma at 100 W of RF power (Fig. 3d) seem to be quite well separated from one another, leaving an empty volume in-between.
3.2. Starch-polyethylene composite materials Composite materials with LDPE as a matrix and starch (both unmodified and modified with methane plasma) as a filler were prepared by means of extrusion. Fig. 4 presents the scanned view of both types of materials (Fig. 4b and c), with a similar view of pure polyethylene, given for a comparison (Fig. 4a). As seen in the figure, already a macroscopic inspection reveals a much better dispersion of the modified starch particles in the matrix, when compared with that of unmodified starch. As a matter of fact, the scanned view of polyethylene filled with modified starch is not much different from that of a pure polyolephine. The cross-sectional SEM micrographs of both composite materials are presented in Fig. 5. The cross-sections were obtained with a microtome technique, using a fracture mirror of glass. The composite with native starch is shown in Fig. 5a, while Fig. 5b presents the composite with starch, modified with methane plasma at 6 sccm of CH4 flow rate and 100 W of RF power. It is evident that the grains of starch are much more uniformly distributed within the matrix in the latter case. This is a result of a deagglomera-
Fig. 4. Scanned views of pure polyethylene (a), polyethylene filled with 20% of native starch (b) and polyethylene filled with 20% of starch modified with methane plasma (c).
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H. Szymanowski et al. / Surface & Coatings Technology 200 (2005) 539 – 543
Fig. 5. SEM micrographs of cross-sections of composite polyethylene/starch material prepared from native starch (a), and from starch modified with methane plasma at the CH4 flow rate of 6 sccm and RF power of 100 Watt (b).
tion process, originating from the surface modification of the starch particles and taking place in the mixing phase of the extrusion. In addition, as opposed to the unmodified grains, the particles have mostly remained in the matrix in the process of the cross-section preparation. This could suggest interaction between the matrix and the filler. 3.3. Testing of the composite materials 3.3.1. Mechanical properties The results of tensile strength tests for LDPE, pure and filled with starch both unmodified and methane plasma modified, are presented in Table 1 for two different concentrations of starch in the matrix. As predicted, pure polyethylene exhibits the best results in the test. On the other hand, strength parameters for polyethylene filled with unmodified starch are the lowest of all. Independent of the concentration, they are considerably higher for those samples that contain starch modified with methane plasma. It would be interesting to find out whether, apart from the deagglomeration effect, there is still another factor, such as filler –matrix interaction, responsible for the improvement of the mechanical behaviour of polyethylene filled with modified starch. This has been attempted with DSC measurements. 3.3.2. Differential scanning calorimetry The DSC measurements were designed to find out whether the presence of starch filler, either unmodified or
methane plasma modified, affect the thermal properties of the polyethylene matrix. Therefore, the polyethylene melting endotherm, obtained in the heating run, was examined for three samples: pure LDPE, LDPE filled with plasma modified starch and LDPE filled with unmodified starch. Its crystallization egzotherm, obtained in the cooling run, was additionally recorded in the former two cases. The results are collected in Table 2. As seen in the table, the presence of starch, independent of whether plasma modified or not, does not alter the melting temperature of polyethylene. A comparison of melting enthalpies brings several additional conclusions. First, the melting enthalpy of LDPE filled with plasma modified starch, amounting to 109.3 J/g, rises to 136.6 J/g, when normalized to 100% of polyethylene. This result is so close to the 134.8 J/g value of the pure polyethylene that it is regarded a further proof of no substantial effect of the filler on the matrix. Similar treatment of the crystallization results gives an additional support of that conclusion. A comparison of both, crystallization temperature and weight normalized enthalpy of crystallization (93.14 J/g for pure LDPE, vs. 74.30/0.8 = 92.87 J/g for LDPE filled with plasma modified starch) strongly suggest a lack of any effect. In addition, the correctness of weight normalization procedures, shown by the agreement of enthalpy data, indicates a very high degree of dispersion of plasma modified starch in the LDPE matrix. In other words, the filler concentration of 20%, introduced at the stage of the extrusion process, is locally repeated in the small specimen,
Table 1 Comparison of mechanical properties of polyethylene materials Type of composite material
Starch content [%]
Maximum stress (MPa)
Elongation at break (%)
Maximum elongation (mm)
Polyethylene Polyethylene + unmodified starch Polyethylene + starch modified with methane plasma at the flow rate of methane 6 sccm and the RF power of 100 W
– 15 15 20
12.46 5.90 9.19 8.53
29.54 9.3 11.21 17.86
22.15 4.66 8.41 13.40
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Table 2 Melting and crystallization data of pure polyethylene and polyethylene filled with starch, as recorded by the DSC technique LDPE
Melting Temperature [-C]
Enthalpy [J/g]
Temperature [-C]
Enthalpy [J/g]
Pure Filled with 20% of native starch Filled with 20% of starch modified with CH4 plasma
111.7 111.5 111.2
134.8 120.6 109.3
99.2 – 99.1
93.1 – 74.3
used in the DSC measurement. This cannot be said about the composite filled with native starch. A comparison of enthalpies of melting gives the local concentration of starch in the DSC sample of (120.6 / 134.8) = 9.4%.
Crystallization
3. An introduction of starch into the polyethylene matrix does not affect its phase transition characteristics. Therefore, there is no indication that an improvement of mechanical properties of the polyethylene/starch composite is due to any interaction between the filler and the matrix.
4. Conclusions The results presented above allow one to draw the following conclusions: 1. RF plasma modification of potato starch may be effectively carried out in a rotary plasma reactor, presented in this work. 2. The described process, with an application of methane plasma, may be used for such modification of starch that prevents agglomeration of its grains, enhances their dispersion in the polyethylene matrix and improves mechanical properties of the composites.
References [1] D.K. Owens, R.C. Wendt, J. Appl. Polym. Sci. 13 (1969) 1741. [2] A.W. Adamson, Physical Chemistry of Surfaces, Interscience Publishers INC, New York, 1960. [3] C. Bamford, K. Al-Lamee, Polymer 37 (1996) 4885. [4] A. Nihlstrand, T. Hjertberg, K. Johanson, Polymer 38 (1997) 3581. [5] J. Gancarz, G. Poz´niak, M. Bryjak, Eur. Polym. J. 35 (1999) 1419. [6] H. Yasuda, Plasma Polymerization, Academic Press, Orlando, 1985. [7] W.J. Van Ooij, A. Chityala, in: K.L. Mittal (Ed.), Polymer Surface Modification; Relevance to Adhesion, vol. 2, VSP Utrecht, 2000, p. 234. [8] N. Inagaki, S. Tasaka, H. Abe, J. Appl. Polym. Sci. 46 (1992) 595.
New biodegradable material based on RF plasma modified starch Hieronim Szymanowskia,*, Mariusz Kaczmareka, Maciej Gazicki-Lipmana, Leszek Klimeka, Bogusaaw Woz´niakb a
Institute for Materials Science and Engineering, Technical University of ‘o´dz´, ‘o´dz´, Poland b Leather Research Institute, ‘o´dz´, Poland Available online 25 May 2005
Abstract The work presents an application of potato starch as a filler for a composite material with high density polyethylene. It was assumed that, in order to improve miscibility of starch with polyethylene matrix, its surface should be made hydrophobic. Therefore, radio frequency (RF) plasma rotary reactor was applied to the surface modification of grains of starch. The plasma reactor was a capacitively coupled RF system equipped with external electrodes. Methane (CH4) was used as working medium. Measurements of a height of water capillary rise were applied to assess the hydrophilic properties of the grain surface. Starch, when modified with methane RF glow discharge, possessed considerably altered surface properties. It was substantially more hydrophobic—the modification process was able to lower capillary rise effect several times. Starch, modified in such a way, was used to prepare composite materials with polyethylene. Tensile strength and elongation at break of the composites were measured. The measurements showed a substantial improvement of mechanical properties of polyethylene samples filled with modified starch, compared to those filled with unmodified starch. Other techniques, such as Scanning Electron Microscopy (SEM) and Differential Scanning Calorimetry (DSC) were also used to characterize the composites. The results of the latter suggest that it was the deagglomeration effects of starch grains resulting in an enhancement of filler dispersion, rather than matrix – filler interaction, that was primarily responsible for the improvement of mechanical properties. D 2005 Elsevier B.V. All rights reserved. Keywords: Potato starch; Plasma processing; Hydrophilicity; Polyethylene; Composite
1. Introduction Polymer wastes constitute today a large ecological problem. Their substantial fraction is comprised of disposable packaging materials of very long composting times, counted in year-hundreds. Under these circumstances, a search for materials of better biodegradability is underway. One of the possible approaches concerns a use of composite systems. In such systems, biodegradable fillers, such as starch, can be used to fill a matrix made of typical thermoplastic polymers, such as polyethylene or polypropylene [1]. There is, however, one major problem with these composites. A polyolefine, with a very low polar component of its surface energy, does not sufficiently wet the surface of starch grains, characterized with a relatively high polar component. An * Corresponding author. Tel.: +48 42 631 22 81; fax: +48 42 636 67 90. E-mail address: [email protected] (H. Szymanowski). 0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.02.213
obvious solution is a minimization of the surface energy of the interface polymer/starch [2]. One way to realize this process is to lower the polar component of surface energy of starch. Low temperature plasma processes have been long used to modify polymer surfaces [3 –6]. A difficulty with the modification of a material used as a filler is its high surface to volume ratio. In other words, the modification of starch requires a plasma system able to work with substrates in a highly particulate form. Fluidal bed plasma reactor is one possibility [7,8]. A system, where the powdered substrate is set in motion, either vibration or rotation, constitutes an alternative solution. 2. Experimental The reactor was equipped with a set of external electrodes, to which the RF power was supplied from the
540
H. Szymanowski et al. / Surface & Coatings Technology 200 (2005) 539 – 543
Fig. 1. Schematic representation of a rotating RF plasma reactor (a), the reactor at work (b).
Plasma Products RF5S power generator through a selfdesigned matching circuit. Methane (CH4) was used as working medium and its flow rate was controlled with the help of a MKS 1179 AX mass flow controller. A starch modification cycle began with setting the flow of CH4, then the rotation of the tubular element with a selected RPM value was introduced, and finally RF glow discharge was generated in the reactor. Powdered starch contained in this reactor was stirred very efficiently, thus enabling an effective plasma surface modification of the grains. The main aim of the modification process was surface hydrophobization of starch, i.e. a substantial decrease of its water contact angle. Therefore, an assessment of the process efficiency comprised measurements of capillary rise of water in glass tubes (1.8 mm in diameter) filled with starch. Methane plasma modified starch was used as a filler to fabricate composite materials with low density polyethylene (LDPE). They were made with the help of a Brabender, model PLP 651, extruder using temperature range of 135– 155 -C and the rate of the screw rotation of 20 RPM. Composites with unmodified starch were also produced for the sake of reference. Extruded materials were then pressed to form foils of a thickness of 0.8 mm, using Nike Eskilstuna press and pressing initial temperature of 180 -C. Tensile tests of the composites were performed with the
help of Instron 5566 tensile testing machine. The size of the specimens has been 4 50 mm. Scanning Electron Microscope (SEM) imaging of starch particles, as well as of the cross-sections of polyethylene/ starch composite materials, was carried out using a Hitachi F 3000 N scanning electron microscope. In order to assure their electrical conductivity the samples were deposited, by means of vacuum evaporation, with a thin film of metallic gold. Differential Scanning Calorimetry (DSC) of the samples was performed using a DSC2920 unit, manufactured by TA Instruments. Both, heating and cooling runs were performed between 150 and 150 -C, with the rate of 10 -C/min.
3. Results 3.1. Hydrophobization of starch Potato starch is considered a hydrophilic material. In our experiments, comprising water capillary rise, the maximum water elevation measured for native starch amounted to approximately 60 mm. Surface modification of starch grains with methane plasma made them substantially more hydrophobic. Fig. 2 presents the results of water capillary elevation for starch modified with methane plasma at the
Fig. 2. Results of capillary elevation measurements for starch modified with methane plasma at the flow rate of 6 sccm (a), at the flow rate of 2 sccm (b).
H. Szymanowski et al. / Surface & Coatings Technology 200 (2005) 539 – 543
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Fig. 3. SEM micrographs of starch grains: unmodified (a), and modified with methane plasma at different RF power values: 20 W (b), 40 W (c), 100 W (d). Flow rate of methane equals 6 sccm.
flow rate of methane equal 6 sccm (2a) and 2 sccm (2b), and at different values of RF power. It is apparent that modification of starch with methane plasma considerably decreases the maximum of water capillary elevation. This is an evidence of hydrophobization of starch grains, taking place in the modification process. SEM micrographs of pure starch filler, both unmodified and methane plasma modified, are presented in Fig. 3. Fig. 3a presents a collection of the unmodified starch grains. As seen in the micrograph, the grains exhibit a tendency towards agglomeration. They form a threedimensional cluster, with some of the particles being located backwards with respect to the others. As indicated by Fig. 3b, c and d, methane plasma modification reduces this tendency and the result depends on RF power input. While the grains modified at 20 W of RF power (Fig. 3b) still appear to form a 3-D cluster, those deposited at higher RF power input apparently form a single-particlethick layer. In addition, starch grains modified with methane plasma at 100 W of RF power (Fig. 3d) seem to be quite well separated from one another, leaving an empty volume in-between.
3.2. Starch-polyethylene composite materials Composite materials with LDPE as a matrix and starch (both unmodified and modified with methane plasma) as a filler were prepared by means of extrusion. Fig. 4 presents the scanned view of both types of materials (Fig. 4b and c), with a similar view of pure polyethylene, given for a comparison (Fig. 4a). As seen in the figure, already a macroscopic inspection reveals a much better dispersion of the modified starch particles in the matrix, when compared with that of unmodified starch. As a matter of fact, the scanned view of polyethylene filled with modified starch is not much different from that of a pure polyolephine. The cross-sectional SEM micrographs of both composite materials are presented in Fig. 5. The cross-sections were obtained with a microtome technique, using a fracture mirror of glass. The composite with native starch is shown in Fig. 5a, while Fig. 5b presents the composite with starch, modified with methane plasma at 6 sccm of CH4 flow rate and 100 W of RF power. It is evident that the grains of starch are much more uniformly distributed within the matrix in the latter case. This is a result of a deagglomera-
Fig. 4. Scanned views of pure polyethylene (a), polyethylene filled with 20% of native starch (b) and polyethylene filled with 20% of starch modified with methane plasma (c).
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H. Szymanowski et al. / Surface & Coatings Technology 200 (2005) 539 – 543
Fig. 5. SEM micrographs of cross-sections of composite polyethylene/starch material prepared from native starch (a), and from starch modified with methane plasma at the CH4 flow rate of 6 sccm and RF power of 100 Watt (b).
tion process, originating from the surface modification of the starch particles and taking place in the mixing phase of the extrusion. In addition, as opposed to the unmodified grains, the particles have mostly remained in the matrix in the process of the cross-section preparation. This could suggest interaction between the matrix and the filler. 3.3. Testing of the composite materials 3.3.1. Mechanical properties The results of tensile strength tests for LDPE, pure and filled with starch both unmodified and methane plasma modified, are presented in Table 1 for two different concentrations of starch in the matrix. As predicted, pure polyethylene exhibits the best results in the test. On the other hand, strength parameters for polyethylene filled with unmodified starch are the lowest of all. Independent of the concentration, they are considerably higher for those samples that contain starch modified with methane plasma. It would be interesting to find out whether, apart from the deagglomeration effect, there is still another factor, such as filler –matrix interaction, responsible for the improvement of the mechanical behaviour of polyethylene filled with modified starch. This has been attempted with DSC measurements. 3.3.2. Differential scanning calorimetry The DSC measurements were designed to find out whether the presence of starch filler, either unmodified or
methane plasma modified, affect the thermal properties of the polyethylene matrix. Therefore, the polyethylene melting endotherm, obtained in the heating run, was examined for three samples: pure LDPE, LDPE filled with plasma modified starch and LDPE filled with unmodified starch. Its crystallization egzotherm, obtained in the cooling run, was additionally recorded in the former two cases. The results are collected in Table 2. As seen in the table, the presence of starch, independent of whether plasma modified or not, does not alter the melting temperature of polyethylene. A comparison of melting enthalpies brings several additional conclusions. First, the melting enthalpy of LDPE filled with plasma modified starch, amounting to 109.3 J/g, rises to 136.6 J/g, when normalized to 100% of polyethylene. This result is so close to the 134.8 J/g value of the pure polyethylene that it is regarded a further proof of no substantial effect of the filler on the matrix. Similar treatment of the crystallization results gives an additional support of that conclusion. A comparison of both, crystallization temperature and weight normalized enthalpy of crystallization (93.14 J/g for pure LDPE, vs. 74.30/0.8 = 92.87 J/g for LDPE filled with plasma modified starch) strongly suggest a lack of any effect. In addition, the correctness of weight normalization procedures, shown by the agreement of enthalpy data, indicates a very high degree of dispersion of plasma modified starch in the LDPE matrix. In other words, the filler concentration of 20%, introduced at the stage of the extrusion process, is locally repeated in the small specimen,
Table 1 Comparison of mechanical properties of polyethylene materials Type of composite material
Starch content [%]
Maximum stress (MPa)
Elongation at break (%)
Maximum elongation (mm)
Polyethylene Polyethylene + unmodified starch Polyethylene + starch modified with methane plasma at the flow rate of methane 6 sccm and the RF power of 100 W
– 15 15 20
12.46 5.90 9.19 8.53
29.54 9.3 11.21 17.86
22.15 4.66 8.41 13.40
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Table 2 Melting and crystallization data of pure polyethylene and polyethylene filled with starch, as recorded by the DSC technique LDPE
Melting Temperature [-C]
Enthalpy [J/g]
Temperature [-C]
Enthalpy [J/g]
Pure Filled with 20% of native starch Filled with 20% of starch modified with CH4 plasma
111.7 111.5 111.2
134.8 120.6 109.3
99.2 – 99.1
93.1 – 74.3
used in the DSC measurement. This cannot be said about the composite filled with native starch. A comparison of enthalpies of melting gives the local concentration of starch in the DSC sample of (120.6 / 134.8) = 9.4%.
Crystallization
3. An introduction of starch into the polyethylene matrix does not affect its phase transition characteristics. Therefore, there is no indication that an improvement of mechanical properties of the polyethylene/starch composite is due to any interaction between the filler and the matrix.
4. Conclusions The results presented above allow one to draw the following conclusions: 1. RF plasma modification of potato starch may be effectively carried out in a rotary plasma reactor, presented in this work. 2. The described process, with an application of methane plasma, may be used for such modification of starch that prevents agglomeration of its grains, enhances their dispersion in the polyethylene matrix and improves mechanical properties of the composites.
References [1] D.K. Owens, R.C. Wendt, J. Appl. Polym. Sci. 13 (1969) 1741. [2] A.W. Adamson, Physical Chemistry of Surfaces, Interscience Publishers INC, New York, 1960. [3] C. Bamford, K. Al-Lamee, Polymer 37 (1996) 4885. [4] A. Nihlstrand, T. Hjertberg, K. Johanson, Polymer 38 (1997) 3581. [5] J. Gancarz, G. Poz´niak, M. Bryjak, Eur. Polym. J. 35 (1999) 1419. [6] H. Yasuda, Plasma Polymerization, Academic Press, Orlando, 1985. [7] W.J. Van Ooij, A. Chityala, in: K.L. Mittal (Ed.), Polymer Surface Modification; Relevance to Adhesion, vol. 2, VSP Utrecht, 2000, p. 234. [8] N. Inagaki, S. Tasaka, H. Abe, J. Appl. Polym. Sci. 46 (1992) 595.