Development and characterizations of jarosite waste reinforced poly(vinyl alcohol) composites: A sustainable approach toward solid waste management

Abstract

Jarosite, an industrial waste, has the potential to be used as an alternative filler in biocomposites used as packaging material and can replace nondegradable thermoplastic. Such a novel approach of waste management strategy has not been studied till date. In this research work, different weight percentages of jarosite were mixed with poly(vinyl alcohol) (PVA) to fabricate polymer composites with better physico-chemical, thermal, tensile, and biodegradation properties. The data indicate that a low concentration of jarosite (3 wt.%) improved the tensile strength by 198.7% and the composite showed higher thermal stability by 6.3% than that of the neat PVA. X-ray diffractogram and transmission electron microscopic analysis revealed a strong interaction between PVA and jarosite. Interestingly, the addition of jarosite reduced the water absorption capacity and thickness swelling of the PVA composite by 58% and 54.7%, respectively. Jarosite-incorporated composites showed lesser degradation potential (64%) than the control composites (84%) after 60 days under soil burial conditions, indicating that PVA-jarosite composites have a higher shelf-life, which is needed for packaging materials. These composites can also be good alternant for thermoplastic used in preparation of cuboid, sealing, and decorative materials. Also, this would be a novel sustainable approach for managing/reducing jarosite waste.

Highlights

• Jarosite was reinforced with PVA to fabricate biocomposites.
• The maximum tensile strength of the composite was achieved as 45.4 MPa.
• The thermal stability of mechanically optimized composite is found at 320°C.
• After 60 days under soil burial, the composite lost 64.8% of its original weight.
• Developed composites can be good alternant for nondegradable thermoplastic.

1 INTRODUCTION

After Leo Baekeland invented the first synthetic plastic, “Bakelite,” in 1907, demand and consumption of plastic were expanded day by day due to its low cost, lightweight, appearance, service temperature, high shelf-life qualities, and user-friendly nature. Once their service life is over, synthetic plastic is a significant environmental risk because most of them are not biodegradable and cause environmental pollution that poses a health threat to human and animal life.¹ Also, these synthetic plastics are sourced from petroleum, which are drastically depleting in today's world. The petroleum resources are nonrenewable in an average time of human settlement hence become scarce very soon. Bioplastic with biodegradable components, holds immense promise for replacing traditional petroleum-based plastics in a variety of applications. Starch, polybutylene adipate terephthalate (PBAT), polyhydroxyalkanoates (PHA), poly(vinyl alcohol) (PVA), polylactic acid (PLA), and so on are some examples of bio-derived plastic.^{2, 3} The environmentally detrimental effects of petroleum-based plastics could be avoided by using bioplastic. However, due to their high cost and poor physical, mechanical, and water resistance qualities, these bioplastics are not easy replacements for nondegradable thermoplastics. Many researchers are now focusing on combining inorganic/organic waste materials with bioplastic to create a viable, lowcost, degradable composite that can compete with the use of conventional thermoplastic in various industries.^4-7

Jarosite is typically an inorganic waste, produces during the zinc purification process in industries. It includes numerous useful elements, that is, zinc, lead, and majorly iron. Jarosite is a basic potassium and iron sulfate, with KFe₃(SO₄)₂(OH)₆ as the molecular formula.⁸ This material has a brittle trigonal crystal structure and a dark yellow color. Traditionally, it has been used to make paving paths, bricks by combining with fly ash,⁹ zinc-iron alloy,¹⁰ removal of hexavalent chromium from wastewater,¹¹ glass fibers,¹² and as a potential adsorbent for hazardous pentavalent arsenic.¹³ According to Asokan et al.,¹⁴ jarosite waste can be immobilized through the production of composite goods that incorporate wastes from coal combustion and marble industries. Although numerous researchers have investigated the possible use of jarosite as an ingredient to cement, its compatibility with bioplastics is yet to be researched, unlike marble dust and granite powder.^{15, 16}

Using PLA and marble dust (MD) waste in different weight ratios, Lendvai et al.¹⁷ developed polymer composites, which showed decrement in tensile strength from 57.9 MPa (neat PLA) to 50.1 MPa of PLA/MD (20 wt.%) composite. The tensile modulus value increased from 2.56 GPA (PLA) to 3.23 GPA for composites containing 20 wt.% MD due to the high stiffness attained by it because of the filler. The flexural stress at conventional deflection of virgin PLA (99.5 MPa) was also increased for its concerned composites up to 10 wt.% of MD content (102.1 MPa) but after that, the value dropped for further MD loading due to its agglomeration in PLA matrix. Abenojar et al.¹⁸ fabricated unsaturated polyester (UPE) matrix-based composites reinforced with 50 wt.% of marble waste and 3 wt.% of glass fiber (short fiber/mesh) and found that the addition of both the fillers increased the flexural strength up to 63 MPa. A similar trend in result was observed in the case of flexural modulus as it rose from 0.6 GPa (UPE matrix) to 1.6 GPa (MD reinforced UPE composite) due to better stress propagation between matrix and filler. The compression strength did not change much on composite formation, that is, 90 MPa for UPE but 90.5 MPa for composites. With the addition of short glass fibers, the resilience strength of the UPE composite was increased, but wear properties were decreased due to the loss of fibers from the matrix. Khan et al.¹⁹ used marble dust as reinforcement with low-density polyethylene matrix (LDPE) to prepare composites and compared its (LDPE-50 wt.% MD) mechanical properties with that of the neat LDPE. The composite showcased improved properties, such as tensile strength of 8.76 MPa over 7.85 MPa, flexural strength of 17.18 MPa over 11.08 MPa, flexural modulus of 704.29 MPa over 244.39 MPa, tensile modulus of 123.4 MPa over 56.19 MPa, and impact strength of 6.60 KJ/m² over 24.98 KJ/m², respectively due to interlinking between MD and LDPE. Chaturvedi et al.²⁰ combined bisphenol-A-diglycidyl ether-based epoxy resin with granite waste powder (GWP) in the presence of curing agent Lapox K-6 amine and coated this modified matrix on different layers of jute fiber to generate sustainable hybrid composites. The properties of the composite containing 60% GWP outperformed that of the epoxy in terms of flexural strength, tensile strength, impact strength, and heat conductivity, each more by 5%, 16%, 148%, and 150%, respectively.

The use of various inorganic fillers in thermoplastic matrices improved some physical and mechanical qualities of their concerned composites. Though PVA, a biodegradable thermoplastic and jarosite, an inorganic industrial waste filler are well abundant, the reinforcing nature of jarosite in PVA has not been thoroughly researched. The current study investigated the suitability of jarosite as reinforcement with PVA along with suitable plasticizers like glycerol, by measuring the physical, mechanical and degradation properties of their concerned composite as an alternative to nondegradable thermoplastic in packaging sector. Plasticizers can further enhance the compatibility and bendability of the formulated composite. This is the first report on the management of solid jarosite waste for the preparation of sustainable PVA-jarosite composite.

1.1 Materials

Merck (India) furnished glycerol ((CH₂OH)₂CHOH, M.W.: 92.09), which was used as a plasticizer and HIMEDIA supplied PVA (AR grade, Mol. wt. 60,000–125,000, degree of hydrolysis 98–100 mol%) as the matrix for composite fabrication. Jarosite [KFe₃(SO₄)₂(OH)₆] (brown yellow powder, trigonal crystal structure, average particle size of 78.8 nm) having an average density of 3.07 g/cm³, was procured from the local market the Bhubaneswar, India.

1.2 Development of PVA-jarosite composites

Varying weight ratios of jarosite (0,1, 2, 3, 4, and 5 wt.%), fixed 5 wt.% of plasticizer and PVA were mixed at a mixing speed of 65 rpm, for 10 min using a magnetic stirrer at room temperature (32°C) and were kept in a hot air oven for drying at 90°C for 24 h. These different sets of PVA-jarosite (PJ) composite films were collected and kept for physical, mechanical, and spectral analysis. Synthesized films with various wt.% (0–5) of jarosite were named PJ0, PJ1, PJ2, PJ3, PJ4, and PJ5, respectively, where the numeric value is the amount of jarosite (in wt.%) that exists in the processed sample.⁴ Digital photographs of jarosite, PJ0 (neat PVA), and PJ3 composite are shown in Figure 1.

FIGURE 1

Digital photographs of (A) jarosite, (B) PJ0, and (C) PJ3 composite.

1.3 Characterizations

1.3.1 Tensile property analysis

Using a Hounsfield H10K-UTM testing machine, with 5 mm/min crosshead speed and temperature of 35 ± 1°C, the tensile properties of PVA-jarosite composites (rectangular test samples of size (64 × 12.7 × 3.2 mm³)), were measured as per ASTM D638-03.⁶ For each type of composite, five specimens were tested and the average value was reported with the standard deviation.

1.3.2 Fourier transform infrared spectroscopy

To verify the plausible interaction between components in PJ composites, Fourier transform infrared (FTIR) analysis of samples using potassium bromide (KBr) reference was recorded in a Thermo Nicolet, Nexus 870 IR spectrometer. The wavenumber range for acquisition was set at 400–4000 cm⁻¹. The samples were powdered and oven-dried at around 80°C, for 24 h before sampling with KBr for pellets.

1.3.3 X-ray diffraction investigation

A WAXD, ULTIMA-III, Rigaku, Japan model X-ray diffractometer, was used to study the lattice of the fabricated film. Ni-filtered Cu-K rays (with a wavelength of 0.154 nm), with a scan velocity of 1/min at 40 kV of voltage and a current of 100 mA were preconditioned for the x-ray diffraction (XRD) study. Using Equation 1, the interlayer (d) arrangement of jarosite was estimated for PVA biocomposites.

$$\mathit{n\lambda }=2d\sin \theta$$ (1)

where “n” denotes the order of reflection, λ is the wavelength of radiation, θ is the diffraction angle, and “d” represents interplanar spacing.

1.3.4 Bulk analysis through transmission electron microscopy studies

HRTEM (JEM-2100, JEOL, Japan) equipment with a 100 kV accelerator voltage and a strong vacuum condition was used for examinations of core structure analysis of PVA-jarosite composites. These composites' powder specimens were mixed with acetone, and an ounce of the resulting solution was dropped into copper foil that was earlier etched with carbon.

1.3.5 Hydrophilicity examination

The hydrophilicity of the PJ films was assessed through the contact angle and water intake tests. A SEO contact angle measuring instrument (Phoenix 300) was used to gauge the contact angle of each specimen at ambient temperature. The specimen size of the sample was kept at 90 × 60 × 6 mm³, which was preweighed (W_i), thickness (T_i) measured and submerged in 1 L of distilled water at RT, for the water sorption testing.² All of the specimens were removed after 24 h and carefully wiped with an absorbent paper to remove excess water from the surface, and the final weight (W_f) and thickness (T_f) were measured. The percentage of water absorption and thickness swelling were calculated using Equations (2) and (3), respectively.

$$\text{Water\hspace{0.17em}absorption}\left(\%\right)=100\times \frac{W_f-W_i}{W_i}.$$ (2)

$$\text{Thickness\hspace{0.17em}swelling}\left(\%\right)=100\times \frac{T_f-T_i}{T_i}.$$ (3)

1.3.6 Thermogravimetric analysis

To evaluate the composite's thermal durability (onset degradation point), thermogravimetric analysis) TGA-209F, Netzsch (Germany) was employed. From 32 to 500°C, the samples were heated in an atmosphere of nitrogen gas at a temperature gradient of 10°C/min.

1.3.7 Soil burial degradation analysis

Before being placed into a compost bed, all PJ specimens were weighed (W₀). As per the BIS1623-92, the compost bed was made in a 2:1:1 ratio combination of the soil from gardens, sandy soil, and cattle dung. These specimens were kept in the incubation for 60 days after their burial.⁴ After the predetermined intervals, the samples were taken off the bed, dirt was scoured off, and the ultimate weight (W₁) was determined. The composites' weight reduction was calculated using following Equation 4.

$$\text{Weightloss}\left(\%\right)=100\times \frac{W_0-W_1}{W_0}.$$ (4)

1.3.8 Surface morphology studies through field emission scanning electron microscopy

Using a field emission scanning electron microscope (FE-SEM) (Vega II, LSU, TESCAN (Czech Republic)), the outermost texture of the materials was analyzed both before and following 60 days of soil burial degradation. As per conventional practice, specimens were gold-coated before fixing on stubs, and at an operating voltage of 5 kV, the pictures of the surface were acquired.

2 RESULTS AND DISCUSSIONS

2.1 Tensile properties analysis

Tensile strength, modulus, and elongation at break values of PJ composite films are shown in Figure 2. Due to the strengthening effect imparted by the micro filler, PJ composites' tensile strength and tensile modulus improved with rising content of jarosite (1–3 wt.%). Neat PVA (PJ0) exhibited 15.2 and 65.7 MPa of tensile strength and modulus respectively, and elongation at break value of 184%, which is nearly equal to the reported values.²¹ With the addition of 1 wt.% of jarosite, the tensile strength and modulus are improved to 30.2 and 74.9 MPa, respectively. Composite PJ3 (3 wt.% jarosite content) showed a tensile strength of 45.4 and tensile modulus of 117.4 MPa respectively, probably due to better interfacial interaction between PVA and jarosite. The presence of jarosite enhanced the roughness of the PVA matrix, allowing for more mechanical interlocking at the interface. The more the available surface area for particles to collide, the faster the interfacial interaction will occur. Interfacial electrostatic interaction may occur because of adhesion between the reinforcement and the matrix.²

FIGURE 2

Tensile analysis of poly(vinyl alcohol)-jarosite composites.

With further addition of jarosite, going up from 3 to 5 wt.%, the tensile properties are reduced due to possible agglomeration of jarosite in PVA resin moiety. Elongation at break value of PJ composites dropped as jarosite content increased because of improved fragility.⁶ PJ3 showed the highest tensile properties among all composites, hence it is considered as mechanically optimized. The possible interaction between PVA and jarosite is given in Figure 3.

FIGURE 3

Schematic interaction between poly(vinyl alcohol) and jarosite in PJ3 composites at the interface.

2.2 FTIR analysis

The existence of chemical connections in the compounds was detected using FTIR spectrum analysis and displayed in Figure 4. The broad peak at around 3595 cm⁻¹ is for the stretching band of OH moieties of neat PVA due to possible intramolecular and intermolecular hydrogen bonding. The strong peaks at roughly 2927 and 2352 cm⁻¹ correspond to CH stretching vibrations from alkyl (CH₂ and CH₃) groups. Peaks with wavenumbers of 1721, 1471, 1306, and 1090 cm⁻¹ in PVA correspond to stretching vibrations of CO, bending vibrations of CH₂ and CH₃ groups, and stretching vibrations of COC group, respectively. For jarosite, peaks obtained at different wavenumbers of 3562, 2346, and 1528 cm⁻¹ are due to OH stretching (for trapped moisture), stretching of SO₄²⁻ group, and water bending group, respectively. A sharp and small peak for jarosite was recorded at 629 cm⁻¹, which is due to the SO₄²⁻ bending vibration that is also reflected in the PJ3 composite at 664 cm⁻¹. The peak at 504 cm⁻¹ represents MO bonding in jarosite.²²

FIGURE 4

Fourier transform infrared analysis of poly(vinyl alcohol)-jarosite composites.

The vibrational stretching bands are detected PJ3 composite at around 3612, 2932^—, and 2352 cm⁻¹ due to OH, CH₂, and CH₃ groups, respectively. The peak for OH stretching (PJ3) obtained at higher wavenumber compared with neat PVA and jarosite indicates the possible formation of the hydrogen bonding between PVA and jarosite when present in such close vicinity (Figure 4). The peaks at wavenumber of 1704 and 1526 cm⁻¹ correspond to stretching vibration of >CO, and bending vibrations of CH₂ and CH₃ groups, respectively. The intensity of >CO peak is slightly broader and shifted toward a lower wavenumber compared with that of the PVA, indicating inorganic–organic interaction in the matrix moiety. The intensity of other peaks (PJ3) is also changed or shifted compared with that of the PVA and jarosite due to their strong secondary interaction.^{23, 24}

2.3 XRD analysis

One of the key elements influencing the mechanical properties of PJ composites is its crystallinity change due to the addition of jarosite, as can be seen in Figure 5. Characteristic peaks for jarosite are found at approximately 15.2°, 16.2°, 18°, and 29.5°, corresponding to the (111), (202), (113), and (022) crystallographic planes, respectively.⁷ Comparatively broader peaks are obtained for PJ0 composite, which comprises solely PVA, is around 19.6° due to semi-crystalline nature of PVA.²⁵ The presence of characteristics of both, jarosite and PVA peak, in the composite confirms the incorporation of both the neat samples. Because of the interaction with PVA, XRD peaks are found to be more/less intense in PJ composites compared with that of the jarosite. The intensities of peaks for jarosite increases as per the incorporated weight percentage of jarosite.

FIGURE 5

X-ray diffraction analysis of (A) jarosite, (B) PJ0, (C) PJ1, (D) PJ2, (E) PJ3, (F) PJ4, and (G) PJ5 composites.

2.4 TEM analysis

Figure 6 depicts transmission electron microscopy (TEM) images of PJ0, PJ3, and PJ5 composite films. TEM images reveal the finest details of the internal structure of the composite at the interface. In Figure 6A, no crystalline layers of jarosite were found as PJ0 is composed of only PVA; rather it has a smooth surface. For PJ3, crystalline planes of jarosite are found in Figure 6B, and they are marked by circles, indicating an intercalation of jarosite layers within the PVA matrix (regularly distributed marked by circle). When the jarosite content reached to 5 wt.%, the crystalline layers were also found largely conglomerated in the PJ5 composite (Figure 6C).²⁶ Jarosite crystalline layers are substantially scattered in all parts of the PVA resin, as indicated by the circle (Figure 6C). In some areas, they are found in an agglomerated state as crystalline layers are overlapped to each other (marked by rectangle), for which the mechanical properties of PJ5 composites were reduced as compared with PJ3 composite.

FIGURE 6

Transmission electron microscopy images of (A) PJ0, (B) PJ3, and (C) PJ5 composites.

2.5 Hydrophilicity test

The hydrophilicity of PJ films as per the angle of contact of water on the surface, is given in Figure 7. Due to the abundance of hydroxyl groups, PVA (PJ0) has a relatively hydrophilic character, for which contact angle (CA) value was found very low (40°). Insertion of jarosite increased the contact angle values, and the highest CA was obtained as 73.4° for PJ3 composite. Contact angle values of PJ1, PJ2, PJ4, and PJ5 composites are found 67.2°, 69.5°, 71.8°, and 65.3° respectively. A high contact angle value indicates less water absorption capacity (hydrophobicity) of material.²⁴

FIGURE 7

Contact angle of (A) PJ0, (B) PJ1, (C) PJ2, (D) PJ3, (E) PJ4, and (F) PJ5 composites.

The percentage of water absorption and thickness swelling of the PVA-jarosite composite is shown in Figure 8. The water absorption values of neat PVA and optimized PJ3 composite are found 220% and 92.4%, whereas thickness swelling values are 227.1% (PJ0) and 102.8% (PJ3), respectively.⁶ An increase in jarosite content from 0 to 3 wt.% in the PJ composites witnesses a drop in water absorption value due to inorganic filler-matrix interaction, which restricted the path of water penetration. However, a higher amount of jarosite loading (>3 wt.%) again increased the water absorption capacity (95.6% for PJ4 and 107.4% for PJ5) and swelling of their concerned composites. With the increase in jarosite content above 3 wt.%, the possible agglomeration of jarosite filler inside PVA-jarosite composite loosened the matrix-filler interaction, hence the water insertion capacity of composite was enhanced.

FIGURE 8

Water absorption and thickness swelling of poly(vinyl alcohol)-jarosite composites.

2.6 TG and derivative thermogravimetric analysis

The TG/derivative thermogravimetric (DTG) analysis of optimized PJ3 and PJ0 is shown in Figure 9. Around 100°C, both the PJ3 and PJ0 composites lost their weight of 2.4% and 3.6%, respectively due to the evaporation of trapped moisture. In the case of PJ0, weight losses of 62.4% at 301°C were obtained due to main chain dehydration and second weight loss of 18% at 428°C for polyene residue degradation, respectively.²⁷ Similarly, for PJ3, DTG peaks are attained near 320 and 441°C for moisture loss of the chain and polyene breakdown with losses in weight of about 62.8% and 9.6%, respectively. For both composites, at 490°C a small degradation occurred due to carbonized residue content (CO₂). So, both PJ0 and PJ3 are heat resilient up to 301 and 320°C, respectively. Hence, jarosite has little effect to improve the thermal stability of PVA-jarosite composite.⁴

FIGURE 9

Thermal analysis of poly(vinyl alcohol) (PJ0) and PJ3 composites.

2.7 Soil burial degradation analysis

Weight loss of PJ composites in soil burial circumstance are shown in Figure 10, after various stages (7, 15, 30, and 60 days). It was discovered that PJ0, which does not contain any jarosite, degrades more rapidly than other PJ composites. A mere 7 days' post-burial analysis of PJ0, PJ1, PJ3, and PJ5 composites, depicted a loss of 20.2%, 14.0%, 10.4% and 13.8% of their original weight, respectively. In all samples, as can be comprehended from the data provided, a prompt depreciation in weight was seen in the initial 30 days of the experiment, and post this the degree of spoilage became slower, which might be due to the quicker action of microorganisms to disintegrate PVA chain in initial periods.²¹ After 60 days, PJ0 lost 84.4% of the mass, but PJ3 lost only 64.8% which could be because of jarosite and its reduced susceptibility to water entry, hence hydrophobic nature and invasion by microorganisms of the compost bed on the face of composites. With the highest percentage of jarosite content, PJ5 composite lost only 68.8% of its original mass after 60 days due to the nondegradable nature of jarosite.²⁴

FIGURE 10

Weight loss of poly(vinyl alcohol)-jarosite (PJ) composites after different biodegradation periods.

SEMs of PJ0, PJ3, and PJ5 composites before and after 60 days of degradation are shown in Figure 11. Figure 11A–C represent the surface of composites before degradation, which are found smooth and homogeneous without any pits or grooves. After 60 days of degradation, composite surfaces got damaged with the formation of pores, gaps, and PVA matrix disintegration on composite surfaces at some places.²⁸ In contrast to PJ3 (Figure 11E) composite, spoiled exteriors of PJ0 (Figure 11D), and PJ5 (Figure 11F) with more cavities and irregular surfaces were evident. From both weight loss and SEM micrographs, it was proved composites are fully biodegradable.

FIGURE 11

Field emission scanning electron micrographs of (A) PJ0, (B) PJ3, (C) PJ5, and after 60 days degradation of (D) PJ0, (E) PJ3, and (F) PJ5 composites.

3 CONCLUSION

PVA and jarosite waste-reinforced composite films were synthesized effectively and characterized by their mechanical properties, thermal stability, hydrophobicity, and biodegradability. Out of all the above, the best-found formulation for PJ composites is PJ3 with 3 wt.% of jarosite content in PVA matrix. The research study indicated that jarosite incorporation in the PVA matrix improved the tensile strength of PJ3 by 199% (45.4 MPa) and tensile modulus (117.4 MPa) by 79% over PJ0 composites. The jarosite-incorporated composites (PJ1-PJ5) are relatively more hydrophobic (92.4% after 24 h) and less biodegradable (64.8% after 60 days under soil burial condition) than those of the non-jarosite containing PVA composite (PJ0). As developed composites are mechanically strong, thermally stable up to 301°C, and biodegradable, they can be used as an alternative to the available thermoplastic in packaging/coating, sealing purposes, decorative materials, indoor articles, and other sectors. Also, this study would open a new arena of sustainable waste management of jarosite for the preparation of value-added products.

ACKNOWLEDGMENTS

We gratefully acknowledge the support provided by DST, Govt. of India and OURIIP, CHSE, Govt. of Odisha for some part of this work.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflicts of interest.

Open Research

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author [Behera, A.K.] upon reasonable request.