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Understanding the behavior of plastics when exposed to various environmental conditions is crucial, as it can lead to degradation, altering the surface properties of the material. This study aims to investigate the underlying causes of degradation in polypropylene (PP) and polyethylene terephthalate (PET) polymers. It also explores the appropriateness of different analytical methods to obtain data and identify trends in polymer behavior.
Polymers undergo physical and chemical changes over time when exposed to heat, light, oxygen, and other environmental factors.
These changes can significantly affect the service life and properties of the materials. Polymer degradation can be induced by various factors, including heat, oxygen, weathering, and biodegradation. In this study, we focus on the degradation of polypropylene (PP) and polyethylene terephthalate (PET) polymers.
Polypropylene is a thermoplastic material widely used in applications such as packaging, consumer products, and textiles. It is known for its resistance to ozone degradation and high temperatures, making it suitable for diverse applications.
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However, only a small percentage of PP is recycled, leading to environmental concerns and the release of toxic gases during slow decomposition.
Polyethylene terephthalate (PET) is a common thermoplastic polymer used for its excellent chemical, thermal, and mechanical properties. It is transparent, semi-crystalline, and widely used in water-resistant applications like bottle packaging. PET is also recyclable, making it commercially important. However, contaminants can impact its degradation.
PET and PP samples were conditioned to promote degradation. PET sheets were prepared by drying at 140°C for 15 hours, followed by hot-pressing into sheets.
PP sheets were hot-pressed at 195°C for 3 minutes and then stored at 70°C for various durations.
FTIR spectrometry was used to study the degree of degradation in polypropylene. It measures the absorption of infrared radiation, allowing us to observe chemical changes in the polymer structure. Absorption bands in the spectra correspond to specific chemical bonds, providing valuable insights.
DSC was employed to analyze the thermal properties of the polymers, including glass transition, melting, and crystallization temperatures. It measures the heat flow required to change the polymer's temperature, providing information about phase transitions and material characteristics.
Tensile tests were conducted to assess the mechanical properties of the polymers. These tests measured stress and strain, yielding data on yield stress, elongation to failure, and ultimate tensile stress.
The FTIR analysis revealed absorption peaks corresponding to chemical changes in the polymer structure. Notably, the region at 1650-1800 cm-1 showed absorption related to carbonyl groups (C=O bonds), indicating chain scission. Hydroperoxide bonds also played a role in degradation, with their presence decreasing over time.
| Sample | Absorption Peak (cm-1) | Identified Bonds |
|---|---|---|
| Undegraded PP | 1710 | C=O (Terminal Ketones) |
| Degraded PP | 1710 | C=O (Terminal Ketones) |
| Undegraded PET | 1650-1800 | C=O Bonds (Carbonyl) |
| Degraded PET | 1650-1800 | C=O Bonds (Carbonyl) |
| Hydroperoxide | 2915 | C-H Bonds |
The DSC results showed that degraded PET exhibited a smaller crystallization peak, suggesting easier crystallization due to reduced heat flow. Crystallinity calculations confirmed this, with degraded PET exhibiting higher crystallinity. The presence of side chains affected crystallinity, resulting in different material properties.
| Sample | Enthalpy of Crystallization (J/g) | Enthalpy of Fusion (J/g) | Tg (°C) | Tm (°C) | Crystallinity (%) |
|---|---|---|---|---|---|
| Undegraded PET | -29.73 | 40.46 | 76 | 250 | 7.66 |
| Degraded PET | -2.13 | 48.95 | 98 | 25 | 33.44 |
Tensile tests indicated that the degradation of PET led to variations in mechanical properties. The 15-minute degraded sample unexpectedly displayed the highest modulus, possibly due to mechanical defects. Yield strength decreased with increased degradation time, with non-degraded PET showing the highest yield strength. Shorter chain lengths correlated with increased brittleness and higher Young's modulus.
| Sample | Young's Modulus (MPa) | Yield Strength (MPa) | Elongation to Break (ETB) |
|---|---|---|---|
| No Degradation | 1002.7 | 51.2 | 3.24 |
| 15min Degradation | 1042.4 | 50.5 | 2.82 |
| 25min Degradation | 885.8 | 24.9 | 0.33 |
The FTIR analysis provided valuable insights into chemical changes in the polymers, confirming the presence of carbonyl groups and the reduction of hydroperoxide bonds with prolonged exposure. The method's sensitivity to degradation conditions, such as high thermal activity, must be considered when interpreting results.
The DSC results demonstrated the impact of degradation on crystallinity, with degraded PET exhibiting easier crystallization. The presence of side chains influenced crystallinity and material properties. Real-world degradation conditions were discussed, highlighting the practical relevance of these findings.
The tensile tests revealed the complex relationship between degradation and mechanical properties. Inclusions and mechanical defects affected the failure points, and shorter chain lengths led to increased brittleness. The discussion touched on the importance of polymer chain entanglement and its influence on material strength.
In conclusion, this study shed light on the degradation behavior of PET and PP polymers under different environmental conditions. FTIR spectrometry, DSC, and tensile tests provided comprehensive insights into chemical, thermal, and mechanical changes in the materials. These findings have practical implications for understanding the degradation of polymers in real-world applications.
Understanding Polymer Degradation: A Comprehensive Study. (2024, Jan 16). Retrieved from https://studymoose.com/document/understanding-polymer-degradation-a-comprehensive-study
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