A recent article in Polymers prepared various plant-filled polymer composites using highly plasticized polyvinyl chloride (PVC) and studied their structural, thermal, and mechanical properties.
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Background
The strength, lightness, and versatility of plastic have significantly integrated it into modern life, with PVC being extensively used across various sectors. However, the long lifespan and non-biodegradability of PVC products have considerable environmental impacts.
Using bio-fillers (such as mineral or vegetable fillers) in PVC composites can enhance their ecological properties by reducing the amount of primary PVC, thus lessening environmental accumulation.
Wood or plant-filled composites control the properties of the final product based on the ratio of PVC to filler. While many researchers have studied three-dimensional products using these composites, plant-filled composites based on highly plasticized PVC as films have rarely been explored.
This study aimed to fill this gap and demonstrate the potential of such materials in producing flooring, fancy goods, or packaging.
Methods
Polymer films (thickness of 500 ± 5 µm) were prepared using an industrial composition of highly plasticized PVC with plant fillers at 0, 20, and 40 wt.%. Spruce flour, lignin-free birch flour, and rice husk, sourced from the woodworking or agricultural industries, were used as fillers.
Various methods were employed to investigate the structural, thermal, and mechanical properties of the composite film samples.
- Structural Analysis: Films were visualized using optical microscopy, and their chemical structure was examined using Fourier transform infrared spectroscopy.
- Thermal Properties: A differential scanning calorimeter was used to determine the glass transition temperature, while thermogravimetric analysis assessed the thermal stability.
- Mechanical Properties: Tests followed International Organization for Standardization (ISO) 527-3:2018 specifications at a 180 mm/min strain rate using an electromechanical testing machine equipped with a 10 kN load cell and a pneumatic gripper.
- Water Absorption: Conducted according to ISO 62:2008 methods using distilled water at room temperature to measure water absorption.
Results and Discussion
The properties of PVC-based composite materials varied depending on the filler type and amount. All plant-filled samples exhibited a low glass transition temperature (below 65°C), indicating maintained elasticity and flexibility at negative temperatures, which is favorable for various operating conditions.
Mechanical tests showed that adding 20 wt.% plant filler reduced the tensile strength by more than half compared to the unfilled composite, with further reductions observed at 40 wt.% filler. The tensile strength decreased from 18.0 MPa to 7.4 MPa with spruce flour and to 5-6 MPa for all filler types at 40 wt.%.
The elongation strength also decreased significantly, necessitating the treatment of plant fillers with appropriate modifiers before use in PVC-based composites.
The plant-filled PVC composites exhibited high water absorption, with the highest (up to 160 mg/g) observed in the polymer containing 40 wt.% rice husk filler. Thus, these composites are unsuitable for applications involving continuous water contact but can withstand repetitive short-term exposure without performance degradation.
Conclusion
The study thoroughly analyzed PVC-based composite materials containing up to 40 wt.% plant fillers. Increasing plant fillers improved the eco-friendliness of plastic-based products but reduced their strength and flexibility, impacting their performance and limiting practical applications.
Despite the significant reduction in thermal and mechanical properties, these composites are suitable for applications where mechanical strength is not critical, such as decorative panels, stationery, and packaging. Additionally, each filler imparts a distinct color to the product, reducing the need for expensive and environmentally hazardous dyes.
Journal Reference
Samuilova, E., Ponomareva, A., Sitnikova, V., Zhilenkov, A., Kichigina, O., Uspenskaya, M. (2024). A Study of Plant-Filled Polymer Composites Based on Highly Plasticized Polyvinyl Chloride. Polymers. doi.org/10.3390/polym1611155
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