PVC vs PLA

Introduction

Polyvinyl chloride (PVC) and polylactic acid (PLA) are two different types of polymers with distinct chemical compositions, and they exhibit different behaviors when it comes to biodegradation. Polyvinyl chloride (PVC) is generally considered non-biodegradable, while polylactic acid (PLA) is biodegradable.

Figure 1: Waste PVC

Polyvinyl Chloride (PVC)

Chemical Composition

PVC is a polymer composed of vinyl chloride monomers, and its distinctive feature lies in the presence of chlorine atoms along the polymer backbone. The carbon-chlorine (C-Cl) bonds contribute to the polymer's chemical stability, making PVC highly resistant to degradation.

Biodegradation Challenges

The chlorine content in PVC is a key factor in its resistance to microbial attack. Microorganisms typically struggle to break the strong carbon-chlorine bonds, resulting in PVC's classification as a non-biodegradable polymer under standard environmental conditions.

Environmental Impact

During degradation or incineration, PVC may release toxic by-products, including hydrochloric acid (HCl) and dioxins. The environmental impact of PVC extends beyond its non-biodegradability, raising concerns about the potential harm caused by these released substances.

Figure 2: Biodegradation material for food packing - PLA and Pulp

Polylactic Acid (PLA)

Chemical Composition

PLA, in contrast, is derived from renewable resources and is composed of lactic acid monomers linked by ester bonds. The ester linkages (-COO-) represent a distinctive feature that plays a crucial role in PLA's biodegradability.

Hydrolysis and Biodegradation

PLA undergoes hydrolysis when exposed to water and microbial activity. In this process, the ester bonds are broken, resulting in the formation of lactic acid monomers. Microorganisms, such as bacteria and fungi, produce enzymes that catalyze the hydrolysis of these ester linkages.

Environmental Advantage

The breakdown products of PLA, primarily lactic acid, are more environmentally benign compared to the potential toxins released during PVC degradation. The natural origin of PLA from renewable resources further adds to its appeal in the context of sustainable chemistry.

Figure 3: Structures of PVC and PLA

Comparing the Chemical Pathways

Microbial Action

PVC's resistance to microbial action stems from the lack of easily cleavable bonds in its structure. The absence of functional groups that attract microorganisms contributes to the overall chemical inertness of PVC.

Ester Linkages and Hydrolysis

PLA's susceptibility to microbial action arises from the presence of ester linkages. These ester bonds are more prone to hydrolysis, a process facilitated by enzymes produced by microorganisms, leading to the breakdown of the polymer into simpler, more environmentally friendly compounds.

Conclusion

In conclusion, the chemistry of PVC and PLA dictates their divergent paths in the realm of biodegradation. PVC's stability, rooted in the strength of carbon-chlorine bonds, renders it non-biodegradable. In contrast, PLA's ester linkages make it susceptible to hydrolysis, allowing for microbial-driven breakdown into components that are more compatible with the environment. Understanding the intricate chemistry of these polymers provides valuable insights for informed decision-making in material selection and environmental stewardship.

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