The most applicable and popular measurement of degradation in thermoplastics is UV irradiation in a weather-o-meter. This practice provides a procedure for performing outdoor-accelerated-exposure testing of plastics and is applicable to a range of plastic materials including plastic films, sheets, laminates and extruded and molded products.
This practice describes the test conditions that attempt to stimulate plastics exposures in desert and sub-tropical climates. Polymer samples can be irradiated in SEPAP 12/24 (from M/s Material Physico Chimique, Neuilly / Marne, France) at desirable temperature in the presence of air. The unit consists of four 400 W ‘Medium Pressure’ mercury vapor sources filtered by a Pyrex envelope supplying radiation of wavelength longer than 290 nm. These sources are located at four corners of a square chamber (~50X50cm). The inside wall of the chamber is made up of high reflection aluminum. Two fans on the wall of the chamber are monitored by a Eurotherm device and afford a regulation of the temperature of samples (± 2° C between 50-65 °C). Thermal degradation can be tested under inert as well as in presence of oxygen in a heating oven. The biodegradation can be studied by several means and countries have their own practice to determine the biodegradability in
polymeric materials. The ASTM and other organizations have developed the standards for testing the biodegradability in different specified conditions (Table 1.2).
Figure 1.2. The possible degradation pathways of polymeric material
• Degradation
(An Irreversible Process leading to a significant change in the structure of a material, typically characterized by a loss of properties and/or fragmentations)
Photo-degradation
(Degradation preceded by light (UV)
Bio-degradation
(Degradation processes in which atleast one step is mediated by biological agents)
Thermal Degradation
(Degradation caused by heat and temperature)
Ultrasonic Degradation
(Degradation caused by Ultrasonic sounds)
High Energy Degradation
(Degradation caused by high energy radiations like X-ray, α,β,γ rays)
Stabilization
(The protection of polymeric materials from which lead to deterioration of properties)
Photo-stabilization
• Screening radiation
• Absorption of radiation
• Radical Scavenging
Bio-stabilization
• Chemical inertness
• Coating of anti-microbial agents
Thermal Stabilization
• Flame Retardancy
• Introduction of thermal stabilizers
High Energy
• Introduction of radiation protectors
Table 1.2. ASTM test methods for determining the biodegradability
1. ASTM D 5247 Determining the Aerobic Biodegradability of Degradable Plastics by Specific Microorganisms
2. ASTM D 6002-96 Guide for Assessing the Compostability of Environmentally Degradable Plastics
3. ASTM D 5338-98 Test Method for Determining Aerobic Biodegradation of Plastic materials under controlled composting conditions.
4. ASTM D 6340-98 Test Methods for Determining Aerobic Biodegradation of Radiolabeled Plastic Materials in an Aqueous or Compost Environment.
5. ASTM D 5209 Test Methods for Determining the Aerobic Biodegradation of Plastic Materials in the presence of Municipal Sewage Sludge 6. ASTM D 5210 Test Methods for Determining the Anaerobic Biodegradation
of Plastic Materials in the presence of Municipal Sewage Sludge
7. ASTM D 5152 Water Extraction of Residual Solids from Degraded Plastics for Toxicity Testing.
The International Organization for Standardization (ISO) is a worldwide federation of national standards bodies (ISO member bodies). Since the working group on biodegradability of plastics was created in 1993, rapid advances have been made in this area. Table 1.3 described the methods for aerobic biodegradation those have recently advanced to Draft of International Standard (DIS) stage.
Table 1. 3. ISO/DIS Methods for the evaluation of biodegradability.
ISO/DIS 14851
Evaluation of the ultimate aerobic biodegradability in an aqueous medium- method by determining the oxygen demand in a closed respirometer
ISO/DIS 14852
Evaluation of the ultimate aerobic biodegradability in an aqueous medium-method by analysis of released carbon dioxide
ISO/DIS 14855
Evaluation of the ultimate aerobic biodegradability and disintegration of plastics under controlled composting conditions- method by analysis of released carbon dioxide
These three ISO/ DIS 14851, 14852 and 14855 are recognized as useful screening tests for establishing the aerobic biodegradability or compostability of plastics.
Some others test methods are DIN (German) DIN 54900-Draft for Evaluation of the compostability and CEN (European) CEN TC 261/ SC4/ WG2 for Evaluation of the compostability, biodegradability and disintegration.
Since all degradation process decreases all the properties of polymers we can use almost all analytical techniques for the evaluation of durability. The characterization of degradation can be carried out by several means those have been summarized in Figure 1.3
Figure 1.3. Different Evaluation methods for degradability
Surface analysis
• ESCA
Morphology
• SEM
• TEM
Crystallinity
• XRD
• DSC
• TGA Physical
Properties
Radicals, ions
• ESR
• Chemi- luminescence
Chemical properties
Functional Changes
• Infrared Spectroscopy
• UV Spectroscopy
• Photophosphoresence
• Chemiluminescence Molecular Weight changes
• GPC (SEC)
• Viscosity Degraded products
• GC
• GCMS
• MALDI-TOF
• LC
Characterization of Polymer Degradation
Mechanical Properties
• Instron
• DMA
Percentage degradation
• Weight Loss
• LSC
• CO2 Estimation (biodegradation)
The study of degradation and stabilization of polymers is an extremely important area from the scientific and industrial point of view. A better understanding of the polymer degradation mechanisms will ensure the long life of the product. Enough attention has not been paid to the study of durability of biocomposites from renewable resources as compared to their preparation techniques and evaluation of material properties.