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Investigation of the biodegradation of low-density polyethylene-starch Bi-polymer blends
Results in Engineering 5 (2020) 100090
Contents lists available at ScienceDirect
Results in Engineering journal homepage: www.editorialmanager.com/rineng/Default.aspx
Investigation of the biodegradation of low-density polyethylene-starch Bi-polymer blends A.A. Abioye *, C.C. Obuekwe Department of Mechanical Engineering, Covenant University, Canaanland, Ota, Nigeria
A R T I C L E I N F O
A B S T R A C T
Keywords: Low-density polyethylene Biodegradable materials Bi-polymer Manihot esculenta Zea mays Ipomoea batatas
Starch is one of the most widely available and easily obtainable natural polymers. This makes it an appealing biobased alternative to synthetic polymers. Yet, the strong intramolecular and inter-molecular hydrogen bonds of starch polymer chains are a major obstacle in its plasticisation. This study showed that starch could be blended with polyethylene to form a partially degradable polymer. The processing conditions and sample formulations were shown to significantly affect the structure of the produced polymers which in turn influenced the degradation properties. Eighteen samples in all were produced by varying the composition of the blends between lowdensity polyethylene and each of Manihot esculenta, Zea mays, or Ipomoea batatas starches. Glycerol and water were employed as plasticizers in this study to reduce friction between polymer chains, improve flexibility, and provide optimal properties. More significantly, results have shown that the produced plastics are environmentally compatible, bio-degradable, compostable, and recyclable. This study has demonstrated the biodegradability of various starch-based polymers in the Sandy-Loamy soil.
1. Introduction There are number of issues associated with contemporary synthetic plastics from non-renewable fossil-based sources [1,2]. These plastics are engineered to be virtually indestructible and may persist for decades in the environment without degrading [3,4]. The non-degradability of synthetic plastics coupled with the multitude of environmental problems they pose has prompted the need for biodegradable alternatives for their replacement in various applicative purposes and for the creation of a sustainable environment. A particular biodegradable bio-based alternative which has garnered widespread interest is starch. Starch is natural polymer and is readily available from various plant sources almost all year round. Starch can be blended with other synthetic polymers in the form of thermoplastic starch (TPS) to produce plastics with improved mechanical properties as compared to that exhibited by TPS such as brittleness and susceptibility to water and humid environments (hydrophilic nature) [5–7]. In order to improve the processability of starch as a thermoplastic polymer and consequently the overall blend, plasticizers can be introduced into the blend. Plasticizers function to downplay the strong intermolecular interactions of the hydrogen bonds between starch molecules thus enhancing the flexibility and workability of starch. Biodegradable polymers with a wide range of properties suitable for
various applicative purposes can be obtained through variation of blend constituents during compounding. This study was aimed at investigating the biodegradability of polymers produced from low-density polyethylene blended with starch from various sources. 2. Methodology Manihot esculenta, Zea mays, Ipomoea batatas, and low-density polyethylene (LDPE) were all locally sourced for this research. The starch extraction process for Zea mays (CoS), Ipomoea batatas (PS), and Manihot esculenta (CaS) was based on the methodology of [8–10] respectively. Glycerol, at one percent concentration, obtained by diluting 10 ml of pure glycerol with 1000 ml of distilled water was utilized as the plasticiser. Low-density polyethylene was measured out alongside starch (of particle size 200 μm) using an OHAUS digital weighing scale at different percentage compositions with the net weight for the blend set at 20 g. The blend composition was then mixed with 30% net sample weight of glycerol (6 g of glycerol). The weighed composition was then poured into a crucible for melting at temperature of 120 C while being mechanically stirred to allowing for prper blending of the various blend constituents. The melting process continued until a homogenous mixture was realized at 130 C, at this point the molten polymer was then poured on an
* Corresponding author. E-mail address: [email protected] (A.A. Abioye). https://doi.org/10.1016/j.rineng.2019.100090 Received 1 November 2019; Received in revised form 19 December 2019; Accepted 20 December 2019 2590-1230/© 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
A.A. Abioye, C.C. Obuekwe
Results in Engineering 5 (2020) 100090
Table 1 Percentage weight loss of LDPE/Manihot esculenta samples. Period
3. Results
LDPE (wt.%) 95
90
85
80
60
50
5.66 7.56 7.83 9.78
4.15 8.07 12.98 18.66
18.73 75.05 76.57 78.05
27.00 45.53 45.79 45.85
The percentage weight losses for the formulated blends are as depicted in Tables 1–3. From the tables it can be seen that biodegradability increased as starch content increased across all the various blend types due to the inherent biodegradability displayed by starch. Heightened levels of biodegradation were experienced particularly at blend compositions of 60 and 50 wt% LDPE which provided a surface for ready microbial invasion in soil environment thereby increasing polymer degradation by biological pathway. Polymer blends of 80 wt% LDPE for all starch types displayed a substantial yet steady rate of biodegradation throughout the 4-week burial period. Biodegradation tests show that all produced polymer blends are biodegradable in soil environment and from percentage weight loss data obtained it can be assumed that these samples would also display promising results in compost environment (home and industrial) and also if interred for longer periods of time. Based on the results of this research, it can be affirmed that starch from Manihot esculenta, Zea mays and Ipomoea batatas can be blended with lowdensity polyethylene at varying compositions for the production of biodegradable polymers with varied properties which can be selected for suitable applications.
Percentage Weight Loss (%) Week Week Week Week
1 2 3 4
1.35 2.01 2.34 2.74
1.42 1.53 1.61 2.50
Table 2 Percentage weight loss of LDPE/Zea mays samples. Period
LDPE (wt.%) 95
90
85
80
60
50
8.91 22.12 43.87 43.94
6.54 9.27 12.91 16.07
4.27 5.76 6.83 7.47
29.15 50.97 68.08 75.41
13.77 23.23 32.64 40.89
Percentage Weight Loss (%) Week Week Week Week
1 2 3 4
10.73 17.94 23.03 27.08
References Table 3 Percentage weight loss for LDPE/Ipomoea batatas samples. Period
[1] A.A. Abioye, O.P. Oluwadare, O.P. Abioye, Environmental impact on biodegradation speed and biodegradability of polyethylene and Ipomoea batatas starch blend, Int. J. Eng. Res. Afr. 41 (2019) 145–154, https://doi.org/10.4028/ www.scientific.net/JERA.41.145. [2] R. Geyer, J.R. Jambeck, K.L. Law, Production, use, and fate of all plastics ever made, Sci. Adv. 3 (2017) 7–12, https://doi.org/10.1126/sciadv.1700782. [3] O.P. Abioye, A.A. Abioye, S.A. Afolalu, S.O. Ongbali, A review of biodegradable plastics in Nigeria, Int. J. Mech. Eng. Technol. 9 (2018) 1172–1185. [4] S.M. Emadian, T.T. Onay, B. Demirel, Biodegradation of bioplastics in natural environments, Waste Manag. 59 (2017) 526–536, https://doi.org/10.1016/ j.wasman.2016.10.006. [5] M.L. Sanyang, S.M. Sapuan, M. Jawaid, M.R. Ishak, J. Sahari, Effect of plasticizer type and concentration on tensile, thermal and barrier properties of biodegradable films based on sugar palm (arenga pinnata) starch, Polymers 7 (2015) 1106–1124, https://doi.org/10.3390/polym7061106. [6] M.L.M. Broeren, L. Kuling, E. Worrell, L. Shen, Environmental impact assessment of six starch plastics focusing on wastewater-derived starch and additives, Resour. Conserv. Recycl. 127 (2017) 246–255, https://doi.org/10.1016/ j.resconrec.2017.09.001. [7] N.S.M. Makhtar, M.F.M. Rais, M.N.M. Rodhi, N. Bujang, M. Musa, K.H.K. Hamid, Tacca leontopetaloides starch: new sources starch for biodegradable plastic, Procedia Eng 68 (2013) 385–391, https://doi.org/10.1016/j.proeng.2013.12.196. [8] D. Platt, Chapter 3 - overview of biodegradable polymers in biodegradable polymers: market report, 26, Smithers Rapra Limited, Shropshire, UK, 2006. [9] A.B. Altemimi, Extraction and optimization of Ipomoea batatas starch and its application as a stabilizer in yogurt manufacturing, Foods 7 (2018) 14–24, https:// doi.org/10.3390/foods7020014. [10] T. Ladeira, H. Souza, R. Pena, Characterization of the roots and starches of three Manihot esculenta cultivars, Int. J. Agric. Sci. Res. 2 (2013) 12–20.
LDPE (wt.%) 95
90
85
80
60
50
28.07 29.42 30.59 31.57
2.58 6.87 8.38 9.20
17.96 32.01 46.88 49.34
36.86 59.58 71.03 76.20
Percentage Weight Loss (%) Week Week Week Week
1 2 3 4
1.03 1.19 1.33 1.37
0.71 0.95 2.32 2.68
aluminium foil and allowed to cure for a period of 24 hours. This procedure was repeated for all the various starch sources at various blend compositions of 95, 90, 85, 80, 60, and 50 wt% of LDPE. The initial weight of all produced blend samples was then measured and recorded. The produced samples were buried in sandy-loam soil at a depth of 4 in. for a period of four (4) weeks during the rainy season in Ota, Ogun, Nigeria. The biodegradation was monitored using the degradation by mass technique where the samples were excavated, weighed, and reinterred following a 7-day cycle. The percentage weight loss was then calculated using the formula below: Percentage weight loss ¼
initial weight present weight 100; initial weight
2
Contents lists available at ScienceDirect
Results in Engineering journal homepage: www.editorialmanager.com/rineng/Default.aspx
Investigation of the biodegradation of low-density polyethylene-starch Bi-polymer blends A.A. Abioye *, C.C. Obuekwe Department of Mechanical Engineering, Covenant University, Canaanland, Ota, Nigeria
A R T I C L E I N F O
A B S T R A C T
Keywords: Low-density polyethylene Biodegradable materials Bi-polymer Manihot esculenta Zea mays Ipomoea batatas
Starch is one of the most widely available and easily obtainable natural polymers. This makes it an appealing biobased alternative to synthetic polymers. Yet, the strong intramolecular and inter-molecular hydrogen bonds of starch polymer chains are a major obstacle in its plasticisation. This study showed that starch could be blended with polyethylene to form a partially degradable polymer. The processing conditions and sample formulations were shown to significantly affect the structure of the produced polymers which in turn influenced the degradation properties. Eighteen samples in all were produced by varying the composition of the blends between lowdensity polyethylene and each of Manihot esculenta, Zea mays, or Ipomoea batatas starches. Glycerol and water were employed as plasticizers in this study to reduce friction between polymer chains, improve flexibility, and provide optimal properties. More significantly, results have shown that the produced plastics are environmentally compatible, bio-degradable, compostable, and recyclable. This study has demonstrated the biodegradability of various starch-based polymers in the Sandy-Loamy soil.
1. Introduction There are number of issues associated with contemporary synthetic plastics from non-renewable fossil-based sources [1,2]. These plastics are engineered to be virtually indestructible and may persist for decades in the environment without degrading [3,4]. The non-degradability of synthetic plastics coupled with the multitude of environmental problems they pose has prompted the need for biodegradable alternatives for their replacement in various applicative purposes and for the creation of a sustainable environment. A particular biodegradable bio-based alternative which has garnered widespread interest is starch. Starch is natural polymer and is readily available from various plant sources almost all year round. Starch can be blended with other synthetic polymers in the form of thermoplastic starch (TPS) to produce plastics with improved mechanical properties as compared to that exhibited by TPS such as brittleness and susceptibility to water and humid environments (hydrophilic nature) [5–7]. In order to improve the processability of starch as a thermoplastic polymer and consequently the overall blend, plasticizers can be introduced into the blend. Plasticizers function to downplay the strong intermolecular interactions of the hydrogen bonds between starch molecules thus enhancing the flexibility and workability of starch. Biodegradable polymers with a wide range of properties suitable for
various applicative purposes can be obtained through variation of blend constituents during compounding. This study was aimed at investigating the biodegradability of polymers produced from low-density polyethylene blended with starch from various sources. 2. Methodology Manihot esculenta, Zea mays, Ipomoea batatas, and low-density polyethylene (LDPE) were all locally sourced for this research. The starch extraction process for Zea mays (CoS), Ipomoea batatas (PS), and Manihot esculenta (CaS) was based on the methodology of [8–10] respectively. Glycerol, at one percent concentration, obtained by diluting 10 ml of pure glycerol with 1000 ml of distilled water was utilized as the plasticiser. Low-density polyethylene was measured out alongside starch (of particle size 200 μm) using an OHAUS digital weighing scale at different percentage compositions with the net weight for the blend set at 20 g. The blend composition was then mixed with 30% net sample weight of glycerol (6 g of glycerol). The weighed composition was then poured into a crucible for melting at temperature of 120 C while being mechanically stirred to allowing for prper blending of the various blend constituents. The melting process continued until a homogenous mixture was realized at 130 C, at this point the molten polymer was then poured on an
* Corresponding author. E-mail address: [email protected] (A.A. Abioye). https://doi.org/10.1016/j.rineng.2019.100090 Received 1 November 2019; Received in revised form 19 December 2019; Accepted 20 December 2019 2590-1230/© 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
A.A. Abioye, C.C. Obuekwe
Results in Engineering 5 (2020) 100090
Table 1 Percentage weight loss of LDPE/Manihot esculenta samples. Period
3. Results
LDPE (wt.%) 95
90
85
80
60
50
5.66 7.56 7.83 9.78
4.15 8.07 12.98 18.66
18.73 75.05 76.57 78.05
27.00 45.53 45.79 45.85
The percentage weight losses for the formulated blends are as depicted in Tables 1–3. From the tables it can be seen that biodegradability increased as starch content increased across all the various blend types due to the inherent biodegradability displayed by starch. Heightened levels of biodegradation were experienced particularly at blend compositions of 60 and 50 wt% LDPE which provided a surface for ready microbial invasion in soil environment thereby increasing polymer degradation by biological pathway. Polymer blends of 80 wt% LDPE for all starch types displayed a substantial yet steady rate of biodegradation throughout the 4-week burial period. Biodegradation tests show that all produced polymer blends are biodegradable in soil environment and from percentage weight loss data obtained it can be assumed that these samples would also display promising results in compost environment (home and industrial) and also if interred for longer periods of time. Based on the results of this research, it can be affirmed that starch from Manihot esculenta, Zea mays and Ipomoea batatas can be blended with lowdensity polyethylene at varying compositions for the production of biodegradable polymers with varied properties which can be selected for suitable applications.
Percentage Weight Loss (%) Week Week Week Week
1 2 3 4
1.35 2.01 2.34 2.74
1.42 1.53 1.61 2.50
Table 2 Percentage weight loss of LDPE/Zea mays samples. Period
LDPE (wt.%) 95
90
85
80
60
50
8.91 22.12 43.87 43.94
6.54 9.27 12.91 16.07
4.27 5.76 6.83 7.47
29.15 50.97 68.08 75.41
13.77 23.23 32.64 40.89
Percentage Weight Loss (%) Week Week Week Week
1 2 3 4
10.73 17.94 23.03 27.08
References Table 3 Percentage weight loss for LDPE/Ipomoea batatas samples. Period
[1] A.A. Abioye, O.P. Oluwadare, O.P. Abioye, Environmental impact on biodegradation speed and biodegradability of polyethylene and Ipomoea batatas starch blend, Int. J. Eng. Res. Afr. 41 (2019) 145–154, https://doi.org/10.4028/ www.scientific.net/JERA.41.145. [2] R. Geyer, J.R. Jambeck, K.L. Law, Production, use, and fate of all plastics ever made, Sci. Adv. 3 (2017) 7–12, https://doi.org/10.1126/sciadv.1700782. [3] O.P. Abioye, A.A. Abioye, S.A. Afolalu, S.O. Ongbali, A review of biodegradable plastics in Nigeria, Int. J. Mech. Eng. Technol. 9 (2018) 1172–1185. [4] S.M. Emadian, T.T. Onay, B. Demirel, Biodegradation of bioplastics in natural environments, Waste Manag. 59 (2017) 526–536, https://doi.org/10.1016/ j.wasman.2016.10.006. [5] M.L. Sanyang, S.M. Sapuan, M. Jawaid, M.R. Ishak, J. Sahari, Effect of plasticizer type and concentration on tensile, thermal and barrier properties of biodegradable films based on sugar palm (arenga pinnata) starch, Polymers 7 (2015) 1106–1124, https://doi.org/10.3390/polym7061106. [6] M.L.M. Broeren, L. Kuling, E. Worrell, L. Shen, Environmental impact assessment of six starch plastics focusing on wastewater-derived starch and additives, Resour. Conserv. Recycl. 127 (2017) 246–255, https://doi.org/10.1016/ j.resconrec.2017.09.001. [7] N.S.M. Makhtar, M.F.M. Rais, M.N.M. Rodhi, N. Bujang, M. Musa, K.H.K. Hamid, Tacca leontopetaloides starch: new sources starch for biodegradable plastic, Procedia Eng 68 (2013) 385–391, https://doi.org/10.1016/j.proeng.2013.12.196. [8] D. Platt, Chapter 3 - overview of biodegradable polymers in biodegradable polymers: market report, 26, Smithers Rapra Limited, Shropshire, UK, 2006. [9] A.B. Altemimi, Extraction and optimization of Ipomoea batatas starch and its application as a stabilizer in yogurt manufacturing, Foods 7 (2018) 14–24, https:// doi.org/10.3390/foods7020014. [10] T. Ladeira, H. Souza, R. Pena, Characterization of the roots and starches of three Manihot esculenta cultivars, Int. J. Agric. Sci. Res. 2 (2013) 12–20.
LDPE (wt.%) 95
90
85
80
60
50
28.07 29.42 30.59 31.57
2.58 6.87 8.38 9.20
17.96 32.01 46.88 49.34
36.86 59.58 71.03 76.20
Percentage Weight Loss (%) Week Week Week Week
1 2 3 4
1.03 1.19 1.33 1.37
0.71 0.95 2.32 2.68
aluminium foil and allowed to cure for a period of 24 hours. This procedure was repeated for all the various starch sources at various blend compositions of 95, 90, 85, 80, 60, and 50 wt% of LDPE. The initial weight of all produced blend samples was then measured and recorded. The produced samples were buried in sandy-loam soil at a depth of 4 in. for a period of four (4) weeks during the rainy season in Ota, Ogun, Nigeria. The biodegradation was monitored using the degradation by mass technique where the samples were excavated, weighed, and reinterred following a 7-day cycle. The percentage weight loss was then calculated using the formula below: Percentage weight loss ¼
initial weight present weight 100; initial weight
2