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Structure–property relation in low-density polyethylene–starch immiscible blends
European Polymer Journal 37 (2001) 943±948
Structure±property relation in low-density polyethylene±starch immiscible blends Baldev Raj a, V. Annadurai b, R. Somashekar b, Madan Raj c, S. Siddaramaiah c,* a
Department of Food Packaging Technology, Central Food Technological Research Institute, Mysore 570 013, India b Department of Physics, University of Mysore, Mysore 570 006, India c Department of Polymer Science and Technology, S.J. College of Engineering, Mysore 570 006, India Received 10 April 2000; received in revised form 27 July 2000; accepted 23 August 2000
Abstract The eect of starch content, on the physico-mechanical properties viz., density, tensile strength and percentage elongation and optical properties like percentage transmittance at dierent wavelengths of low-density polyethylene/ starch blended ®lms has been investigated. The changes have been interpreted quantitatively in terms of microcrystalline parameters compiled using wide angle X-ray scattering data. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Low-density polyethylene; Starch; Immiscible blend; X-ray study
1. Introduction Increasing public concern over dwindling land®ll space and accumulation of surface litter has promoted the development of degradable plastics [1±4]. Commercial biodegradable ®lms are generally manufactured from low-density polyethylene (LDPE) with degradable additives such as starch and pro-oxidants [5]. A signi®cant amount of plastic is used to package food products. If corn starch-containing plastic ®lm has no adverse effects on food quality or food safety, its use in food packaging could lead to decreased petrochemical usage and increased starch utilization. Starch-®lled PE ®lms have been reported by many researchers [6±10], but there is lack of literature on structure±property relation in LDPE±starch. Polymer blends, immiscible or miscible, are proven to be a new way for developing new materials with properties suitable for packaging industry. In view of recent thrust eco-friendly packaging materials, the research in
*
Corresponding author. Fax: +91-0821-515440. E-mail address: [email protected] (S. Siddaramaiah).
this area has been made signi®cant in developing new materials. One such materials happen to be LDPE± starch polymer blends and in this article we have examined LDPE blended with varying concentration of starch. There are signi®cant changes in optical and mechanical properties in these blends which we have tried to correlate with microstructural parameters obtained from wide angle X-ray scattering (WAXS).
2. Experimental 2.1. Materials LDPE and starch (commercial grade) were obtained from M/s. IPCL, India and M/s. Sd. Fine chemicals Ltd., India respectively. A series of LDPE/starch composites were prepared by varying the starch content from 2.5% to 70% by solvent method, using CCl4 as a solvent. LDPE granules were dissolved in CCl4 at its boiling point and calculated amount of starch was dispersed by stirring. The mixture of all starch±LDPE were compounded twice to achieve uniform starch±LDPE mixing. The compounded material was stored in a sealed container within a desiccator to prevent atmospheric
0014-3057/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 0 0 ) 0 0 1 9 3 - 2
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B. Raj et al. / European Polymer Journal 37 (2001) 943±948
moisture absorption. The mixture was dried and blended powder was obtained. The LDPE/starch ®lms were prepared by thermopress casting machine at 140±150°C under 150 kg/cm2 pressure. The cast ®lms with a 70±80 lm thickness were collected and stored in polyethylene bags at 4°C.
2.2. Methods The density was measured as per ASTM D-792 method. The tensile strength and percentage of elongation were measured as per ASTM D-882 method using Instron Universal Testing machine (model 4302). Tests were performed using at least ®ve samples in each case and the average value is reported. All tests were performed at ambient temperature.
The percentage of transmittance of light was measured using UV±Vis spectrophotometer UV 1601 at different wavelengths.
2.3. X-ray pro®le analysis X-ray recordings were carried on all samples using JEOL, Japan diractometer. The settings used are the following; 35 kV, 15 mA and the wavelength of radia These recordings are given in tion used was k 1:934 A. Fig. 1. The crystal imperfection parameters like crystal size hNi and lattice strain (g) were determined by employing Fourier method of Warren and Hosemann's one-dimensional paracrystalline model where the simulated intensity pro®le was matched with experimental one [11±13] (see Fig. 2(a) and (b)). Following equations were employed to simulate the wide angle X-ray pro®le. I s
1 X
A n cosf2pnd s
s0 g
1
n 1
where A n is the product of size coecient As n and lattice distortion (strain coecient) Ad n. The expression and explanation of the various notations are
Fig. 1. Wide angle X-ray scattering for patterns for pure LDPE and blends of LDPE with dierent starch contents.
Fig. 2. (a) and (b) Experimental and calculated X-ray pro®le for (2 1 0) and (2 1 1) re¯ections in LDPE with 40% starch.
B. Raj et al. / European Polymer Journal 37 (2001) 943±948
given in our earlier paper [14]. Using HosemannÕs onedimensional paracrystalline model we have the following relations [13]: I s IN 1 s IN1 s
2
where, "
1 I N 1 It IN s 2Re 1 I d 1 I2 # N
fI N 1
I 1
1
1g
3
where, t 2Ia2 s d;
I I1 s exp a2 s2 ids;
a2 x2 =2: Also, IN1 s
2aN D p1=2
exp iDs1
aN sf2D aN s
i p1=2 exp a2N s2 g
4
with a2N N x2 =2, x is the standard deviation of the nearest neighbour probability function, D aN s is the DawsonÕs integral or the error function with complex argument and can be computed. hN i is the number of unit cells counted in a direction perpendicular to the (h k l) Bragg plane, d is the spacing of the (h k l ) planes, ÔReÕ refers to the real part of the expression, s is sin h=k, k is the wavelength of X-rays used, a is related to the standard deviation x of the lattice distribution function and D is the crystal size hN idh k l . IN1 s is the modi®ed intensity for the probability peak centered at
945
D. These microcrystalline parameters are given in Table 3.
3. Results and discussion The measured density, tensile strength and percent elongation of LDPE/starch ®lms are shown in Table 1. From the table it was noticed that the density of LDPE/ starch systems lies in the range of 0.9348±1.311 g/ml. Density of blended ®lms were in the increasing order with increase in starch content. This is due to density of pure LDPE is 0.92 g/ml and it is lower than the density of starch (1.488 g/ml). The tensile strength which is a measure of the resistance to direct pull is of importance in machinability and packaging applications. It was observed from Table 1 that the tensile strength decreased from 110 kg/cm2 of plain LDPE casted by thermopressed mechanism to 40 kg/cm2 in 50% starch ®lled LDPE ®lm [15±17]. The tensile strength of 110 kg/cm2 in LDPE ®lm, prepared by compression method, was lesser than that of LDPE ®lm prepared by extrusion method. (240 kg/cm2 ). This is due to the molecular orientation eect. There was a drastic reduction in tensile behavior with increase in the starch content in LDPE ®lms. Tensile strength values lies in the range 107±40 kg/cm2 for starch ®lled LDPE. The percentage of elongation had decreased with incorporation of starch. This is due to the fact that starch has low tensile strength and percent elongation compared to LDPE. Physically, incorporation of starch in the matrix of LDPE weakens the London forces between LDPE layers and hence, decrease in elongation. Percentage of transmission of all LDPE/starch ®lms were presented in Table 2 and the value decreased with increase in concentration of starch [15,16]. This is ascribed due to starch is immiscible in LDPE matrix and
Table 1 Physico-mechanical properties of the starch ®lled LDPE composite LDPE ®lms with starch (%)
Density q (g/ml)
Deviation (%)
Tensile strength (kg/cm2 )
Deviation (%)
Percent elongation
Deviation (%)
Pure LDPE 2.5 5 7.5 10 15 20 30 40 50
0.9210 0.9348 0.9486 0.9620 0.9740 1.0320 1.074 1.148 1.208 1.311
±
110 107 103 98 91 85 75 67 58 40
±
52 48 45 43 39 35 29 23 15 8
±
1.50 3.00 4.45 5.75 12.0 16.61 24.65 31.16 42.35
5.5 10.9 13.6 18.2 22.7 31.8 39.1 47.3 54.8
7.7 13.5 17.3 25.0 32.7 44.2 55.8 71.1 84.6
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B. Raj et al. / European Polymer Journal 37 (2001) 943±948
Table 2 Percent transmittance at dierent wavelength (measured by UV±Vis spectrophotometer) for starch ®lled LDPE ®lms Sample LDPE (pure) LDPE 2:5% starch LDPE 5% starch LDPE 7:5% starch LDPE 10% starch LDPE 15% starch LDPE 20% starch LDPE 30% starch LDPE 40% starch LDPE 50% starch LDPE 70% starch
% Transmittance at dierent wavelengths 400 nm
500 nm
600 nm
700 nm
65 61
69 64
72 67
75 70
56
61
65
67
53
57
60
64
50
54
58
62
47
52
55
60
45
50
54
58
43
47
51
55
42
47
51
55
38
44
49
53
27
33
38
33
also incorporation of starch induces amorphous behavior of LDPE matrix. WAXS recording for pure LDPE and its blends with dierent starch contents are shown in Fig. 1. From Fig. 1 it was observed that, only two well separated re¯ections were appeared in the range of 2h value 26±28 (2 1 0) and 29.7±32.2 (2 1 1) [18]. The computed microstructural parameters for various LDPE/starch blends were given in Table 3. Fig. 2(a) and (b) show the goodness of the ®t between simulated and experimental pro®le for (2 1 0) and (2 1 1) re¯ection in LDPE with 40% of starch. These results are further justi®ed by the behavior of microstructural quantities like crystal size and lattice strain, at the microscopic level as seen from Table 3. In fact, if one looks at the eect of concentration of starch in LDPE on these microstructural parameters, which is given in Fig. 3(a) and (b), we observe that a least squares ®t to data show that microcrystalline parameters decreases with concentration of starch in LDPE. In fact, for a change of 70% of starch in LDPE, we observe 10% and 2% change in crystal size and lattice distortion respectively of the lattice. From Table 3 it is rather dicult to arrive at any de®nite conclusion, as there are signi®cant changes in the microcrystalline parameters.
Table 3 Unit cell and microstructural parameters for the composition of LDPE and starch Sample
2h degree
Re¯ection
hN i
p
a
g (%)
a
dh k l (A)
D (A)
LDPE (pure)
27.39 32.17
(2 2 0) (3 1 1)
23.10 0.5 11.13 0.1
18.02 6.27
0.241 0.206
5:81 0:1 7:43 0:1
0.28 0.25
4.080 3.490
94.25 38.84
LDPE 2:5% starch
28.00 31.10
(3 0 0) (3 1 1)
23.13 0.3 8.43 0.1
18.92 0.54
0.135 0.127
5:48 0:1 7:53 0:1
0.26 0.22
3.997 3.607
94.45 30.40
LDPE 5% starch
26.92 30.19
(2 0 0) (2 1 0)
24.73 0.3 8.12 0.2
18.95 0.001
0.173 0.123
5:18 0:1 7:16 0:2
0.26 0.20
4.150 3.713
102.63 30.15
LDPE 7:5% starch
27.11 30.22
(3 2 0) (4 0 0)
17.83 0.3.1 9.71 0.1
15.94 4.40
0.530 0.190
6:22 0:1 4:90 0:1
0.26 0.13
4.126 3.170
73.57 30.02
LDPE 10% starch
27.50 30.50
(3 0 0) (3 1 1)
18.52 0.3 14.23 0.1
14.78 9.110
0.268 0.195
6:21 0:1 6:10 0:1
0.27 0.23
4.068 3.680
75.34 52.37
LDPE 15% starch
27.25 30.22
(3 0 0) (3 1 1)
28.60 0.5 8.81 0.1
20.73 0.95
0.127 0.127
5:24 0:1 4:85 0:1
0.28 0.14
4.105 3.710
117.40 32.69
LDPE 20% starch
27.92 30.92
(3 0 0) (3 1 1)
30.28 0.5 8.43 0.1
21.62 0.01
0.116 0.119
5:03 0:1 5:89 0:1
0.28 0.17
4.008 3.628
121.36 30.58
LDPE 30% starch
27.10 30.34
(2 0 0) (2 1 1)
20.72 0.4 8.72 0.1
16.72 5.10
0.250 0.276
5:86 0:1 5:35 0:1
0.27 0.16
4.127 3.730
85.51 32.53
LDPE 40% starch
27.11 29.84
(2 1 0) (2 1 1)
13.94 0.1 6.05 0.1
1.34 0.001
0.080 0.165
4:99 0:1 4:04 0:1
0.19 0.10
4.126 3.756
57.52 22.72
LDPE 50% starch
27.03 29.65
(2 1 0) (2 1 1)
13.40 0.1 4.10 0.1
1.80 0.001
0.086 0.106
5:30 0:1 4:31 0:1
0.19 0.09
4.138 3.779
55.45 15.49
LDPE 70% starch
27.58 30.22
(2 1 0) (2 1 1)
17.12 0.1 6.43 0.1
9.09 0.001
0.125 0.155
5:54 0:1 4:00 0:1
0.23 0.10
4.057 3.710
69.46 23.86
B. Raj et al. / European Polymer Journal 37 (2001) 943±948
947
Fig. 3. (a) Variation of crystal size (2 1 1) re¯ection with composition of LDPE/starch. (b) Variation of lattice strain (g in %) (2 1 1) re¯ection with composition of LDPE/starch.
By taking crystal size obtained for (2 1 0) and (2 1 1) re¯ections along x-axis and y-axis, we can approximately observe the changes in terms of shape of crystallites. Fig. 4(a) and (b) show such changes. It is evident from these Fig. 4 that changes occur only on the periphery of the crystallite domains. From these parameters we can also estimate the minimum enthalpy which de®nes the equilibrium state of microparacrystals in LDPE/starch blends at dierent compositions using the relation [19], a hN i1=2 g:
5
This a value implies physically that, the growth of para crystals in a particular material is appreciably controlled by the level g in the net plane structure. These estimated value of enthalpy is also given in Table 3. From the Table 3 it is evident that, the percentage of starch content in LDPE blend do not aect the value of a . The reason for such changes can be attributed to indiscriminate of starch granules in the matrix of LDPE, which generally tends to lower the short range interaction between the layers of LDPE leading to increase in disorder of the lattice. These changes result in more broadening of X-ray Bragg re¯ections, which we have quanti®ed in terms of microstructural parameters. On a
Fig. 4. (a) and (b) Show the variation in crystallite shape ellipsoid with % of starch in LDPE ®lms.
macroscopic scale these do eect the physical parameters like tensile strength, percentage of elongation and percentage of transmittance (see Fig. 5(a)±(c)), which we have presented here. 4. Conclusions Starch modi®ed LDPE ®lms have marginal reduction in tensile strength and percent elongation values due to
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B. Raj et al. / European Polymer Journal 37 (2001) 943±948
Acknowledgements Authors thank Prof. C.I.V. Shastry, NIE, Mysore for assistance in computation.
References
Fig. 5. Variation of (a) tensile strength, (b) percentage elongation and (c) transmittance (500 nm) with crystal size for dierent percentage of starch in LDPE ®lms.
decrease in short range forces which in turn increases the amorphous region. The extent of changes in the amorphous/crystalline region have been quanti®ed in the form of lattice strain (g) and the crystal size values (N ). This study establishes the structure dependent physical property of starch modi®ed LDPE ®lms.
[1] Grin GJ. Biodegradable synthetic resin sheet material containing starch and a fatty material. US Patent 4, 016,117, 1977. [2] Otey FH, Mark A. Biodegradable starch-based agricultural mulch ®lm. US Patent 3,949,145. [3] Leet B, Pometto AL, Fratzke A, Bailey TB. Appl Environ Microbial 1991;57:678±85. [4] Roper H, Koch H. Starch/Starke 1990;42:123±30. [5] Gage P. Degradable polyethylene ®lm ± the fact. Tappi J 1990;10:161±9. [6] Grin GJ. Adv Chem Ser 1974;34:159±70. [7] Seung-taik L, Jane J-L. Biotechnol Prog 1992;8:51±7. [8] Evapngelista RL, Nikolov ZL, Sung W, Jane J, Gelina RJ. Ind Engng Chem Res 1991;30:1841. [9] Fanta GF, Swanson CL, Doane WM. J Appl Polym Sci 1990;40:811±21. [10] Evangelista RL, Nikolar ZE, Sung W, Jane JL, Gelina RL. Ind Engng Chem Res 1993;30:1841±6. [11] Somashekar R, Somashekarappa H. J Appl Cryst 1997; 30:147. [12] Somashekar R, Hall IH, Carr PD. J Appl Cryst 1989; 22:363. [13] Hall IH, Somashekar R. J Appl Cryst 1991;24:105. [14] Somashekarappa H, Somashekar R, Singh V, Ali SZ. Bull Mater Sci 1999;22:101. [15] Lawton JW. Carbohydr Polym 1996;29:203±8. [16] Lim S, Jane J. Biotechnol Prog 1992;8:51±7. [17] Baldev Raj, Siddaramaiah S. Abstract Int Conf on Polymers for 21st Century, New Delhi, 2000. p. 21±3. [18] De Wol PM. J Appl Cryst 1968;1:108. [19] Hosemann R. Colloid Polym Sci 1982;268:982.
Structure±property relation in low-density polyethylene±starch immiscible blends Baldev Raj a, V. Annadurai b, R. Somashekar b, Madan Raj c, S. Siddaramaiah c,* a
Department of Food Packaging Technology, Central Food Technological Research Institute, Mysore 570 013, India b Department of Physics, University of Mysore, Mysore 570 006, India c Department of Polymer Science and Technology, S.J. College of Engineering, Mysore 570 006, India Received 10 April 2000; received in revised form 27 July 2000; accepted 23 August 2000
Abstract The eect of starch content, on the physico-mechanical properties viz., density, tensile strength and percentage elongation and optical properties like percentage transmittance at dierent wavelengths of low-density polyethylene/ starch blended ®lms has been investigated. The changes have been interpreted quantitatively in terms of microcrystalline parameters compiled using wide angle X-ray scattering data. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Low-density polyethylene; Starch; Immiscible blend; X-ray study
1. Introduction Increasing public concern over dwindling land®ll space and accumulation of surface litter has promoted the development of degradable plastics [1±4]. Commercial biodegradable ®lms are generally manufactured from low-density polyethylene (LDPE) with degradable additives such as starch and pro-oxidants [5]. A signi®cant amount of plastic is used to package food products. If corn starch-containing plastic ®lm has no adverse effects on food quality or food safety, its use in food packaging could lead to decreased petrochemical usage and increased starch utilization. Starch-®lled PE ®lms have been reported by many researchers [6±10], but there is lack of literature on structure±property relation in LDPE±starch. Polymer blends, immiscible or miscible, are proven to be a new way for developing new materials with properties suitable for packaging industry. In view of recent thrust eco-friendly packaging materials, the research in
*
Corresponding author. Fax: +91-0821-515440. E-mail address: [email protected] (S. Siddaramaiah).
this area has been made signi®cant in developing new materials. One such materials happen to be LDPE± starch polymer blends and in this article we have examined LDPE blended with varying concentration of starch. There are signi®cant changes in optical and mechanical properties in these blends which we have tried to correlate with microstructural parameters obtained from wide angle X-ray scattering (WAXS).
2. Experimental 2.1. Materials LDPE and starch (commercial grade) were obtained from M/s. IPCL, India and M/s. Sd. Fine chemicals Ltd., India respectively. A series of LDPE/starch composites were prepared by varying the starch content from 2.5% to 70% by solvent method, using CCl4 as a solvent. LDPE granules were dissolved in CCl4 at its boiling point and calculated amount of starch was dispersed by stirring. The mixture of all starch±LDPE were compounded twice to achieve uniform starch±LDPE mixing. The compounded material was stored in a sealed container within a desiccator to prevent atmospheric
0014-3057/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 0 0 ) 0 0 1 9 3 - 2
944
B. Raj et al. / European Polymer Journal 37 (2001) 943±948
moisture absorption. The mixture was dried and blended powder was obtained. The LDPE/starch ®lms were prepared by thermopress casting machine at 140±150°C under 150 kg/cm2 pressure. The cast ®lms with a 70±80 lm thickness were collected and stored in polyethylene bags at 4°C.
2.2. Methods The density was measured as per ASTM D-792 method. The tensile strength and percentage of elongation were measured as per ASTM D-882 method using Instron Universal Testing machine (model 4302). Tests were performed using at least ®ve samples in each case and the average value is reported. All tests were performed at ambient temperature.
The percentage of transmittance of light was measured using UV±Vis spectrophotometer UV 1601 at different wavelengths.
2.3. X-ray pro®le analysis X-ray recordings were carried on all samples using JEOL, Japan diractometer. The settings used are the following; 35 kV, 15 mA and the wavelength of radia These recordings are given in tion used was k 1:934 A. Fig. 1. The crystal imperfection parameters like crystal size hNi and lattice strain (g) were determined by employing Fourier method of Warren and Hosemann's one-dimensional paracrystalline model where the simulated intensity pro®le was matched with experimental one [11±13] (see Fig. 2(a) and (b)). Following equations were employed to simulate the wide angle X-ray pro®le. I s
1 X
A n cosf2pnd s
s0 g
1
n 1
where A n is the product of size coecient As n and lattice distortion (strain coecient) Ad n. The expression and explanation of the various notations are
Fig. 1. Wide angle X-ray scattering for patterns for pure LDPE and blends of LDPE with dierent starch contents.
Fig. 2. (a) and (b) Experimental and calculated X-ray pro®le for (2 1 0) and (2 1 1) re¯ections in LDPE with 40% starch.
B. Raj et al. / European Polymer Journal 37 (2001) 943±948
given in our earlier paper [14]. Using HosemannÕs onedimensional paracrystalline model we have the following relations [13]: I s IN 1 s IN1 s
2
where, "
1 I N 1 It IN s 2Re 1 I d 1 I2 # N
fI N 1
I 1
1
1g
3
where, t 2Ia2 s d;
I I1 s exp a2 s2 ids;
a2 x2 =2: Also, IN1 s
2aN D p1=2
exp iDs1
aN sf2D aN s
i p1=2 exp a2N s2 g
4
with a2N N x2 =2, x is the standard deviation of the nearest neighbour probability function, D aN s is the DawsonÕs integral or the error function with complex argument and can be computed. hN i is the number of unit cells counted in a direction perpendicular to the (h k l) Bragg plane, d is the spacing of the (h k l ) planes, ÔReÕ refers to the real part of the expression, s is sin h=k, k is the wavelength of X-rays used, a is related to the standard deviation x of the lattice distribution function and D is the crystal size hN idh k l . IN1 s is the modi®ed intensity for the probability peak centered at
945
D. These microcrystalline parameters are given in Table 3.
3. Results and discussion The measured density, tensile strength and percent elongation of LDPE/starch ®lms are shown in Table 1. From the table it was noticed that the density of LDPE/ starch systems lies in the range of 0.9348±1.311 g/ml. Density of blended ®lms were in the increasing order with increase in starch content. This is due to density of pure LDPE is 0.92 g/ml and it is lower than the density of starch (1.488 g/ml). The tensile strength which is a measure of the resistance to direct pull is of importance in machinability and packaging applications. It was observed from Table 1 that the tensile strength decreased from 110 kg/cm2 of plain LDPE casted by thermopressed mechanism to 40 kg/cm2 in 50% starch ®lled LDPE ®lm [15±17]. The tensile strength of 110 kg/cm2 in LDPE ®lm, prepared by compression method, was lesser than that of LDPE ®lm prepared by extrusion method. (240 kg/cm2 ). This is due to the molecular orientation eect. There was a drastic reduction in tensile behavior with increase in the starch content in LDPE ®lms. Tensile strength values lies in the range 107±40 kg/cm2 for starch ®lled LDPE. The percentage of elongation had decreased with incorporation of starch. This is due to the fact that starch has low tensile strength and percent elongation compared to LDPE. Physically, incorporation of starch in the matrix of LDPE weakens the London forces between LDPE layers and hence, decrease in elongation. Percentage of transmission of all LDPE/starch ®lms were presented in Table 2 and the value decreased with increase in concentration of starch [15,16]. This is ascribed due to starch is immiscible in LDPE matrix and
Table 1 Physico-mechanical properties of the starch ®lled LDPE composite LDPE ®lms with starch (%)
Density q (g/ml)
Deviation (%)
Tensile strength (kg/cm2 )
Deviation (%)
Percent elongation
Deviation (%)
Pure LDPE 2.5 5 7.5 10 15 20 30 40 50
0.9210 0.9348 0.9486 0.9620 0.9740 1.0320 1.074 1.148 1.208 1.311
±
110 107 103 98 91 85 75 67 58 40
±
52 48 45 43 39 35 29 23 15 8
±
1.50 3.00 4.45 5.75 12.0 16.61 24.65 31.16 42.35
5.5 10.9 13.6 18.2 22.7 31.8 39.1 47.3 54.8
7.7 13.5 17.3 25.0 32.7 44.2 55.8 71.1 84.6
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B. Raj et al. / European Polymer Journal 37 (2001) 943±948
Table 2 Percent transmittance at dierent wavelength (measured by UV±Vis spectrophotometer) for starch ®lled LDPE ®lms Sample LDPE (pure) LDPE 2:5% starch LDPE 5% starch LDPE 7:5% starch LDPE 10% starch LDPE 15% starch LDPE 20% starch LDPE 30% starch LDPE 40% starch LDPE 50% starch LDPE 70% starch
% Transmittance at dierent wavelengths 400 nm
500 nm
600 nm
700 nm
65 61
69 64
72 67
75 70
56
61
65
67
53
57
60
64
50
54
58
62
47
52
55
60
45
50
54
58
43
47
51
55
42
47
51
55
38
44
49
53
27
33
38
33
also incorporation of starch induces amorphous behavior of LDPE matrix. WAXS recording for pure LDPE and its blends with dierent starch contents are shown in Fig. 1. From Fig. 1 it was observed that, only two well separated re¯ections were appeared in the range of 2h value 26±28 (2 1 0) and 29.7±32.2 (2 1 1) [18]. The computed microstructural parameters for various LDPE/starch blends were given in Table 3. Fig. 2(a) and (b) show the goodness of the ®t between simulated and experimental pro®le for (2 1 0) and (2 1 1) re¯ection in LDPE with 40% of starch. These results are further justi®ed by the behavior of microstructural quantities like crystal size and lattice strain, at the microscopic level as seen from Table 3. In fact, if one looks at the eect of concentration of starch in LDPE on these microstructural parameters, which is given in Fig. 3(a) and (b), we observe that a least squares ®t to data show that microcrystalline parameters decreases with concentration of starch in LDPE. In fact, for a change of 70% of starch in LDPE, we observe 10% and 2% change in crystal size and lattice distortion respectively of the lattice. From Table 3 it is rather dicult to arrive at any de®nite conclusion, as there are signi®cant changes in the microcrystalline parameters.
Table 3 Unit cell and microstructural parameters for the composition of LDPE and starch Sample
2h degree
Re¯ection
hN i
p
a
g (%)
a
dh k l (A)
D (A)
LDPE (pure)
27.39 32.17
(2 2 0) (3 1 1)
23.10 0.5 11.13 0.1
18.02 6.27
0.241 0.206
5:81 0:1 7:43 0:1
0.28 0.25
4.080 3.490
94.25 38.84
LDPE 2:5% starch
28.00 31.10
(3 0 0) (3 1 1)
23.13 0.3 8.43 0.1
18.92 0.54
0.135 0.127
5:48 0:1 7:53 0:1
0.26 0.22
3.997 3.607
94.45 30.40
LDPE 5% starch
26.92 30.19
(2 0 0) (2 1 0)
24.73 0.3 8.12 0.2
18.95 0.001
0.173 0.123
5:18 0:1 7:16 0:2
0.26 0.20
4.150 3.713
102.63 30.15
LDPE 7:5% starch
27.11 30.22
(3 2 0) (4 0 0)
17.83 0.3.1 9.71 0.1
15.94 4.40
0.530 0.190
6:22 0:1 4:90 0:1
0.26 0.13
4.126 3.170
73.57 30.02
LDPE 10% starch
27.50 30.50
(3 0 0) (3 1 1)
18.52 0.3 14.23 0.1
14.78 9.110
0.268 0.195
6:21 0:1 6:10 0:1
0.27 0.23
4.068 3.680
75.34 52.37
LDPE 15% starch
27.25 30.22
(3 0 0) (3 1 1)
28.60 0.5 8.81 0.1
20.73 0.95
0.127 0.127
5:24 0:1 4:85 0:1
0.28 0.14
4.105 3.710
117.40 32.69
LDPE 20% starch
27.92 30.92
(3 0 0) (3 1 1)
30.28 0.5 8.43 0.1
21.62 0.01
0.116 0.119
5:03 0:1 5:89 0:1
0.28 0.17
4.008 3.628
121.36 30.58
LDPE 30% starch
27.10 30.34
(2 0 0) (2 1 1)
20.72 0.4 8.72 0.1
16.72 5.10
0.250 0.276
5:86 0:1 5:35 0:1
0.27 0.16
4.127 3.730
85.51 32.53
LDPE 40% starch
27.11 29.84
(2 1 0) (2 1 1)
13.94 0.1 6.05 0.1
1.34 0.001
0.080 0.165
4:99 0:1 4:04 0:1
0.19 0.10
4.126 3.756
57.52 22.72
LDPE 50% starch
27.03 29.65
(2 1 0) (2 1 1)
13.40 0.1 4.10 0.1
1.80 0.001
0.086 0.106
5:30 0:1 4:31 0:1
0.19 0.09
4.138 3.779
55.45 15.49
LDPE 70% starch
27.58 30.22
(2 1 0) (2 1 1)
17.12 0.1 6.43 0.1
9.09 0.001
0.125 0.155
5:54 0:1 4:00 0:1
0.23 0.10
4.057 3.710
69.46 23.86
B. Raj et al. / European Polymer Journal 37 (2001) 943±948
947
Fig. 3. (a) Variation of crystal size (2 1 1) re¯ection with composition of LDPE/starch. (b) Variation of lattice strain (g in %) (2 1 1) re¯ection with composition of LDPE/starch.
By taking crystal size obtained for (2 1 0) and (2 1 1) re¯ections along x-axis and y-axis, we can approximately observe the changes in terms of shape of crystallites. Fig. 4(a) and (b) show such changes. It is evident from these Fig. 4 that changes occur only on the periphery of the crystallite domains. From these parameters we can also estimate the minimum enthalpy which de®nes the equilibrium state of microparacrystals in LDPE/starch blends at dierent compositions using the relation [19], a hN i1=2 g:
5
This a value implies physically that, the growth of para crystals in a particular material is appreciably controlled by the level g in the net plane structure. These estimated value of enthalpy is also given in Table 3. From the Table 3 it is evident that, the percentage of starch content in LDPE blend do not aect the value of a . The reason for such changes can be attributed to indiscriminate of starch granules in the matrix of LDPE, which generally tends to lower the short range interaction between the layers of LDPE leading to increase in disorder of the lattice. These changes result in more broadening of X-ray Bragg re¯ections, which we have quanti®ed in terms of microstructural parameters. On a
Fig. 4. (a) and (b) Show the variation in crystallite shape ellipsoid with % of starch in LDPE ®lms.
macroscopic scale these do eect the physical parameters like tensile strength, percentage of elongation and percentage of transmittance (see Fig. 5(a)±(c)), which we have presented here. 4. Conclusions Starch modi®ed LDPE ®lms have marginal reduction in tensile strength and percent elongation values due to
948
B. Raj et al. / European Polymer Journal 37 (2001) 943±948
Acknowledgements Authors thank Prof. C.I.V. Shastry, NIE, Mysore for assistance in computation.
References
Fig. 5. Variation of (a) tensile strength, (b) percentage elongation and (c) transmittance (500 nm) with crystal size for dierent percentage of starch in LDPE ®lms.
decrease in short range forces which in turn increases the amorphous region. The extent of changes in the amorphous/crystalline region have been quanti®ed in the form of lattice strain (g) and the crystal size values (N ). This study establishes the structure dependent physical property of starch modi®ed LDPE ®lms.
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