Development of Biodegradable Plastics from Sago and Bario Rice Blends

Development of Biodegradable Plastics from Sago and Bario

Rice Blends

Syed Mohammed Sajl

Semester 6B Tech – PS & E

Tuesday, April 11, 2023 1Review Seminar - Semester 5

Abstract

• In this study, Bioplastics with mechanical and water absorption properties are prepared from Natural Polymers.

• Biodegradable plastic composites were prepared by casting thermoplastic starches (Bario Rice/Sago starch at ratio 2:3) with natural rubber (0.5 - 10 %) in the presence of a plasticizer (glycerol).

• Mixtures of Sago and Bario Rice starch are blended with natural rubber latex with the presence of Plasticizer.

• Here, thermoplastic starch is the dispersed phase and natural rubber latex as filler.

• Bioplastics produced were characterized by Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Water absorption test, Biodegradable Test and Mechanical analysis.

Tuesday, April 11, 2023 Review Seminar - Semester 5 3

Ecological Relevance

• Plastics are widely used since 1980s.• Petroleum-derived plastics have poor

biodegradability and may last hundreds of years when buried in typical solid waste sites.

• This leads to environmental pollution which is a real threat to total ecosystem.

• So, there is much interest in Edible and Biodegradable Films from Natural Polymers as alternatives to Synthetic Polymers.

Biodegradable Plastics

• Biodegradable plastics are plastics that can be biologically broken down, in a reasonable amount of time, into their base compounds.

• They may be composed of:1)"Bioplastics", whose components are

derived from renewable raw materials2)Traditional petroleum-based plastics

containing biodegradable additives which allow them to enhance the biodegradation of plastic.

• Under proper conditions biodegradable plastics can degrade to the point where microorganisms can completely metabolize them to carbon dioxide and water.

• Examples:•Naturally Produced: Polyhydroxyalkanoates (PHAs) like the poly-3-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and polyhydroxyhexanoate (PHH)•Renewable Resource: Polylactic acid (PLA)•Synthetic: Polybutylene succinate (PBS), polycaprolactone (PCL).

• Sago is a starch extracted in the spongy center, or pith, of various tropical palm stems, especially, Metroxylon sagu.

• Sago is often produced commercially in the form of "pearls".

• Sago pearls can be boiled with water or milk and sugar to make a sweet sago pudding.

• Sago starch is also used to treat fibre, making it easier to machine.

Sago Pearls

Bario Rice

• Bario Rice is a local product cultivated by hand with no pesticides or herbicides and represents a valuable ecological niche.

• The Kelabit tribe, who live solely Malaysian village located in the centre of the Kelabit Highlands grow the rice.

• Bario Rice is a medium grain rice, marble white in color. This variety is famous for its excellent sweet taste and slightly sticky texture, and is a favorite among Malaysian chefs that use it to prepare traditional recipes.

Bario Rice

Experiment

Materials

• Natural Rubber Latex from Hevea brasilensis trees.

• Sago Starch supplied from any foodstuff Company

• Rice Starch derived from Bario rice cultivar

• Glycerol• Sodium Hydroxide

Film Preparation

• Films are prepared from rice and sago starch.• Rice and Sago starches (3% w/w) are

gelatinized in an autoclave at 120OC, 100 kPa for 30 minutes.

• Glycerol is added as the Plasticizer at 30% (w/w) relative to starch.

• Thermoplastic Starch/Natural Rubber Latex (TPS/NRL) samples of 100/0, 99.5/0.5, 98.51.5, 97.5,2.5, 96.5/3.5, 93.0/7 and 90/10 are prepared by adding natural latex in required proportions.

• The prepared solutions are homogenized with an ultrasonic homogenizer with 30% power for 5 minutes.

• The products are dried at room temperature for 3 days before overnight oven drying at 50oC.

Characterization

• Mechanical Properties: Film products are tested for elongation at break and tensile strength using Universal Testing Machine.

• Differential Scanning Calorimetry (DSC): Film products of 15mg were encapsulated in Tzero Aluminum Pans. Sample Pans are heated at 20oC/min from 20 to 200oC. Tm is recorded.

• Fourier Transform Infrared Spectroscopy (FTIR): Fourier Transform Infrared Spectra are recorded between 4000 and 400 cm-1

• Water Absorption: Water absorption test was conducted by using film products of sixze 1.5 x 3.0 cm. The films are dried for 6 hours at 50oC and weighed. The samples are then soaked in distilled water at 23±1oC. Samples are weighed periodically every week for 4 weeks.

• Biodegradability Studies: 3 Biodegradability tests are conducted.Water Hydrolysis Test is carried out by soaking the samples of size 1.5 x 3.0 cm in in 20 ml of distilled water at 70oC. The changes in weight are recorded every 2 hours.

Alkaline Hydrolysis Test is carried out by soaking the samples of size 1.5 x 3.0 cm in in 20 ml of 0.1M Sodium Hydroxide solution at 70oC. The changes in weight are recorded every 30 minutes. Soil burial test was conducted by burying the samples of size 3.0 x 3.0 cm into mineral soil. Samples are rinsed with distilled water and dried in an oven at 50oC for 24 hours and weighed. The test is conducted at 15, 30, 60 and 90 days after soil burial

Results

Mechanical Properties

• The tensile strength and elongation at break of Thermoplastic Starch/Natural Rubber Latex (TPS/NRL) blends are summarized in the table.

• The addition of increasing natural rubber latex resulted in decreasing tensile strength and increased elongation at break in Thermoplastic Starch/Natural Rubber Latex (TPS/NRL) blends.

• Blends which had 7 and 10% (w/w) natural rubber latex content were found to have elongation at break of 483% and 570% respectively.

BLENDS(TPS/NRL)

Tensile Strength (MPa)

Elongation at Break (%)

100/0 11.2 16.7

99.5/0.5 9.4 16.7

98.5/1.5 6.7 16.7

97.5/2.5 6.0 13.3

96.5/3.5 4.7 20.0

93.0/7.0 4.4 483.3

90.0/10.0 3.6 570

Table: Mechanical Properties of Thermoplastic Starch/Natural Rubber Latex Blends

Thermal Profile

• Results revealed that endotherms of pure thermoplastic starch, the blend with lowest natural rubber latex content and the blend with highest natural rubber latex content showed complete melting at 138, 146 and 161oC respectively.

• This indicates a higher melting point (Tm)for blends with higher natural rubber latex content than that for thermoplastic. It is clear that melting temperature increased as the rubber content increased in Thermoplastic Starch/Natural Rubber Latex blends.

BLENDS(TPS/NRL)

Melting Temperature

Tm (oC)

100/0 138

99.5/0.5 146

98.5/1.5 155

97.5/2.5 155

96.5/3.5 154

93.0/7.0 156

90.0/10.0 161

Table: DSC Thermal Profile of Thermoplastic Starch/Natural Rubber

Latex Blends

Fourier Transform Infrared Spectroscopy (FTIR)

• The FTIR spectra of thermoplastic starch alone showed characteristic O-H stretching bands within the 3650-3000 cm-1 region, C-H stretching bands within 2927 cm-1 region, C=C stretching bands within 1680-1620 cm-1 region, cyclohexane ring vibrations bands within 1055-925 cm-1 region and O-H deformation bands within 900-400 cm-1 region.

• All the bands were present in Thermoplastic Starch/Natural Rubber Latex (TPS/NRL) blends except at 1567 cm-1 and 1538 cm-1

Figure: FTIR Spectra of Thermoplastic Starch/Natural Rubber Latex Blends: (a) Blend TPS/NRL 90/10 (b)

Blend TPS/NRL 100/0

Water Absorption

• Thermoplastic Starch/Natural Rubber Latex (TPS/NRL) blends with higher natural rubber latex blends with higher natural rubber latex content exhibited better water resistance compared to samples with less natural rubber content.

• In the first 7 days, the blend containing 10% natural rubber latex absorbed 31.4% of water.

• However, the blend without natural rubber latex absorbed 47.5% of water in the first week.

• The water absorption slowly increased over a period of 28 days.

• Blends of 93.0/7.0 and 90.0/10.0 composition have lower water absorption compared to others.

Figure: Percentage Weight Gain of Thermoplastic Starch/Natural Rubber Latex Blends during Water

Absorption

Biodegradability Studies

• The blends with low thermoplastic starch lost weight significantly in the first 2 hours.

• A constant weight was achieved for all blends after 2 hours of treatment.

• In alkaline hydrolysis test, high rubber blends showed significant weight losses in the first 30 minutes and then maintained a constant weight.

• Accelerated alkaline hydrolysis resulted in higher weight losses as compared to water hydrolysis.

• The soil burial test has been known to be a slow process due to the low percolation rate.

• The test indicated lower losses than those determined by both types of hydrolysis testing after 15 days, but at the end of 90 days, the measured losses almost equaled the losses in samples subjected to water hydrolysis for 12 hours or alkaline hydrolysis for 150 minutes.

• Samples with only thermoplastic starch were degraded faster than samples that had been added with natural rubber latex.

• Samples with the highest rubber latex content showed the lowest degradation rate.

Table: Weight Loss % of Thermoplastic Starch/Natural Rubber Latex (TPS/NRL) blends after exposure to Water and Alkaline Hydrolysis at Temperature 70oC and buried

in soil.

Discussion

• Addition of natural rubber latex results in decreased tensile strength and increased elongation at break in Thermoplastic Starch/Natural Rubber Latex (TPS/NRL) blends .

• The elongation at break was found to correlate with the theoretically predicted values for systems with good adhesion and is generally considered to be highly sensitive to the state of interface.

Thermal Profile

• The study revealed that endotherms for blends with lower natural rubber latex content and blends with higher natural rubber latex content, it showed complete melting at 146 and 161oC respectively.

• Thermoplastic Starch/Natural Rubber Latex (TPS/NRL) blends are thermoplastic polymers and upon application of heat, undergo a process of fusion or melting where the crystalline character is destroyed.

• The crystallinity of blends with higher natural rubber content was found to be more than thermoplastic starch alone.

Fourier Transform Infrared Spectroscopy (FTIR)

• The FTIR spectra of blends showed a similar region of wave number and characteristic bands for starch.

• The NR band found in the blend with natural rubber latex was due to addition of Ammonia solution in latex for stabilization.

• The OH bands are unreliable for quantitative analysis due to their dependence on water content and atmospheric condition.

Water Absorption

• The blends with higher natural rubber latex content exhibited poorer water absorption.

• The addition of hydrophobic particles (natural rubber latex) to a hydrophilic component enhances the water resistance of the blended samples.

Biodegradability Studies

• Accelerated alkaline hydrolysis resulted in higher weight loss as compared to water hydrolysis due to the presence of the NaOH, which enhances the solubilization and gelatinization of starch in the polymer blend.

• The soil burial test showed that the higher the natural rubber latex content of the sample, the lower the degradation rate because the latter structure has higher miscibility and compatibility and formed a dense structure within the sample.

Conclusion

• Rubber latex and Starch blends showed a wide range of physical and mechanical properties.

• Natural rubber latex acted as a good inert filler as it decreased the tensile strength but increased the elongation at break.

• Addition of natural rubber latex demonstrated higher product elongation at break, water resistant ability, melting temperature and slower biodegradability.

• The blends with higher natural rubber latex fitting were less vulnerable to degradation.

References

•Development of Biodegradable Plastics from Sago and Bario Rice BlendsSie-Cheong Kiing, Shir-Yih Ee, Sie-Chuong Wong, Amartalingam Rajan and Pang HungyiuJournal of Polymer Materials (Vol 28, No 3) – July – Sept 2011•www.wikipedia.com•www.google.com

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Development of Biodegradable Plastics from Sago and Bario Rice Blends

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