Effect Of Thermal Treatment On Physical And Chemical Properties Of Recycled Polypropylene

Project and Seminar Material for Chemistry

Effect Of Thermal Treatment On Physical And Chemical Properties Of Recycled Polypropylene


Polypropylene is widely used today in industries and also at home and its production has increase drastically over the years making polypropylene products a major contributor in environmental waste. Therefore, instead of throwing away wasted or unusable polypropylene to where it may cause harm to the environment and the whole biodiversity, recycling comes to rescue. The objective of this study is to determine the change in properties of polypropylene with recycling. For this purpose, the mechanical properties of polypropylene using five recycling generation were determined.

The polypropylene materials were cut into flakes and pretreated before recycled mechanically at 180-2100C with fabricated mold. ASTM D638 type II specimen dimensions was chosen for tensile test. Ultimate tensile stress test relates the mechanical properties such as tensile strength, elastic modulus and percent elongation to failure to the recycling generations.

The curves which were generated prove that the polypropylene properties decrease with recycling. FTIR analysis affirmed that the chemical structures of the material were not affected by the recycling process.

However, the slight decrease in properties can be compensated by adding a virgin polypropylene at a ratio before recycling. Conservative safety factors and plastics additives, filler inclusion can also correct the decrement.
Recycling of plastic materials is effective in conserving the environment and enhancing the life cycle of these materials.

Table of Contents

  • Title Page
  • Letter of Transmittal
  • Certification
  • Dedication
  • Acknowledgement
  • Abstract
  • Table of Contents
  • List of Tables
  • List of Figures
  • List of Abbreviations

Chapter One:


  • 1.1 Background
  • 1.2 Project objective
  • 1.3 Justification

Chapter Two:

Literature Review

  • 2.1 Plastics
  • 2.2 Plastic recycling
  • 2.2.1 Polyethylene Terephthalate
  • 2.2.2 Polyethylenes
  • 2.2.3 Polyvinyl chloride
  • 2.2.4 Polystyrene
  • 2.3 Polypropylene
  • 2.3.1 History of polypropylene
  • 2.3.2 Molecular structure of polypropylene
  • 2.3.3 Properties of polypropylene
  • 2.3.4 Applications of polypropylene
  • 2.4 Physical and Chemical Testing
  • 2.4.1 Fourier Transform Infrared Spectroscopy (FTIR)
  • 2.4.2 Ultimate Tensile Strength (Ultimate tensile stress (UTS))

Chapter Three:


  • 3.1 Material Selection
  • 3.1.2 Material pretreatment
  • 3.2.2 Fabrication of Mold
  • 3.2 Experimental Procedure
  • 3.3 Testing
  • 3.3.1 Fourier Transform infrared spectroscopy
  • 3.3.2 Mechanical testing

Chapter Four:

Results and Discussion

  • 4.1 FTIR Analysis
  • 4.2 Mechanical Properties
  • 4.1.1 Ultimate Tensile Strength
  • 4.1.2 Elasticity Modulus
  • 4.1.3 Elongation Percent
  • 4.1.4 Tensile Stress and Strain

Chapter Five:

Conclusion and Recommendations

  • 5.1 Conclusion
  • 5.2 Recommendation
  • References
  • Appendices

List of Tables

  • Table 2.1: Table of Resin Identification Codes for Different Plastics
  • Table 2.2: The mechanical properties of polypropylene and its values
  • Table 3.1: Calculated pressure summary table
  • Table 4.1: IR table of functional groups according to their range
  • Table 4.2: Summarized Ultimate tensile stress (UTS) data for each generation
  • Table 4.3: Summarized Elasticity Modulus
  • Table 4.4: Elongation Percent data for each recycled generation
  • Table I: Results for 1st Generation
  • Table II: Results for 2nd Generation
  • Table III: Results for 3rd Generation
  • Table IV: Results for 4th Generation
  • Table V: Results for 5th Generation

List of Figures

  • Figure 2.1: Schematic of the nature of chain branching varieties of polyethylene
  • Figure 2.2: Structure of polypropylene monomer types
  • Figure 3.1a: Waste Polypropylene materials gathered for the experiment
  • Figure 3.1b: Pre-treated polypropylene flakes
  • Figure 3.2: Experimental Set up
  • Figure 3.3: First generation sample from first run
  • Figure 3.4: Typical Dog bone shaped ASTM D638 specimen used for Tensile test
  • Figure 3.5: Typical Stress-Strain diagram
  • Figure 4.1: FTIR spectrum of 1stgeneration sample
  • Figure 4.2: Reference IR polypropylene spectrum
  • Figure 4.3: IR spectrum of 2nd generation
  • Figure 4.3: IR spectrum of 3rdgeneration
  • Figure 4.3: IR spectrum of 4th generation
  • Figure 4.4: FTIR spectrum of 5th generation
  • Figure 4.5: Linear regression of Ultimate tensile stress (UTS) for all generations
  • Figure 4.6: Elastic Modulus vs recycled generation trend
  • Figure 4.7 Elongation percent vs recycling generation
  • Figure 4.8: Tensile stress strain diagram for 1st recycling generations
  • Figure 4.9: Tensile stress strain diagram for 2ndrecycling generations
  • Figure 4.10: Tensile stress strain diagram for 3rdrecycling generations
  • Figure 4.11: Tensile stress strain diagram for 4threcycling generations
  • Figure 4.12: Tensile stress strain diagram for 5threcycling generations
  • Figure A: Comparison of the stress strain for all generation

List of Abbreviations

  • UTS Ultimate Tensile Strength
  • UTM Universal Testing Machine
  • ASTM American Society of Testing and Materials
  • PET, PETE Polyethylene terephthalate
  • PE Polyethylene
  • PP Polypropylene
  • LPDE Low-density polyethylene
  • HDPE High-density polyethylene
  • LLDPE Linear low-density polyethylene
  • PVC Polyvinyl chloride
  • PS Polystyrene
  • ABS Acrylonitrile- butadiene-styrene
  • SAN Styrene-acrylonitrile
  • SMA Styrene-maleic anhydride
  • BOPP Biaxially oriented film
  • FTIR Fourier Transform Infrared Spectroscopy
  • DTA Differential Thermal Analysis
  • DSC Differential Scanning Calorimetry
  • ATR Attenuated Total Reflectance

Chapter One


1.1 Background

During last decades, the great population increase worldwide together with the need of people to adopt improved conditions of living led to a dramatically increase of the consumption of polymers (mainly plastics). Materials appear interwoven with our consuming society where it would be hard to imagine a modern society today without plastics which have found a myriad of uses in fields as diverse as household appliances, packaging, construction, medicine, electronics, and automotive and aerospace components. A continued increase in the use of plastics has led to increase the amount of plastics ending up in the waste stream, which then becomes a threat to the environment when the wastes are not decomposable(Hamad et al., 2013). Environmental issues are becoming prioritized in most government and community development agendas. This has motivated the search for economically efficient and ecologically effective material and energy recycling technologies (Petts, 2000). For example, the development and use of strategic technologies driven by recycling credit scheme and the imposition of the landfill tax to preserve landfill void for the future disposal of untreatable residues in England(Read et al.,1998). The potential environmental impacts from plastics are categorized under global warming, acidification, eutrophication and photochemical ozone creation(Bos et al., 2007).

Polypropylene account for around 22% of the total production of plastics in 2008, making it the second largest plastic produced beside polyethylene which is 23.7% (Plastic waste Management Institute, 2009).Polypropylene plastics or also known as polypropene, are materials that are used worldwide since the 19th century (Scheirs, 1998). Polypropylene plastics are widely used in our daily life as kitchen utensils, in toy productions, as insulators for electrical devices, and also in industrial sites as safety equipment(Gaurina-Medijumurec, 2014). Since polypropylene is widely used today in industries and also at home, its production has increase drastically over the years with increasing production of polypropylene made products. Therefore, polypropylene products is a major contributor to the pollution in the world today and now acting as a threat to both man and the whole biodiversity(Anthony, 2003). Itsnon-biodegradability makes post-consumer polypropylene a major environmental issue. Disposal of polypropylene waste by burning is not an environmentally friendly as the gases released are toxic.

Several options have been considered to reduce polypropylene waste such as reuse and recycling (Aurrekoetxeaet al., 2011). The most common examples of reuse are with glass containers, where milk and drinks bottles are returned to be cleaned and used again(Hamad et al., 2013). Reuse is not widely practiced in relation to plastic packaging of plastic products in general tend to be discarded after first use. However, there are examples of reuse in the marketplace. For example, a number of detergent manufacturers market refill sachets for bottled washing liquids and fabric softeners. Consumers can refill and hence reuse their plastic bottles at home, but in all of these cases the reusing of the plastic bottles and containers do not continue for long time especially in the food applications which makes recycling the best alternative.

Mechanical recycling and chemical recycling are the most widely practiced of these methods. However, from industrial point of view, the mechanical recycling is the most suitable because its low cost and reliability (Hamad et al., 2013). Mechanical recycling also known as physical recycling, the plastic is ground down and then reprocessed and compounded to produce a new component that may or may not be the same as its original use (Cui and Forssberg, 2003).

As to this, the recycling of post-consumer polypropylene polymer products is one of the factors in reducing the amount of wastes material produced every day (Harold, 2003). However, until today, the research on the mechanical properties of recycled polypropylene is not widely explored in open literature. Besides that, not much input of the properties of the recycled products either in mechanical or physical properties is comparable with the pure polypropylene materials. Thus, the study on the mechanical properties of the recycled polypropylene product is necessary.

1.2 Project Objective

The main objective of this project are:

  1. To design and fabricate a mold for purpose of this research
  2. To determine how physical and chemical properties of polypropylene changes with recycling.

1.3 Justification

Polymer recycling is a way to reduce environmental problems caused by polymeric waste accumulation generated from day-to-day applications of polymer materials such as in packaging and construction. The recycling of polymeric waste helps to conserve natural resource because the most of polymer materials are made from oil and gas. Since recycling has been a solution to reduce environmental problem therefore the limit at which the properties of the materials produce through this method is of high importance.

It is proven theoretically that polypropylene materials take a long time for the properties to deteriorate and also reduce cost of production since no or little virgin polymer is required and energy is conserved.

Chapter Five

Conclusion and Recommendations

5.1 Conclusion

It is obvious from the experimental data that the mechanical properties are affected as a result of recycling. Principally, mechanical properties decrease with recycled generations. From the last chapter, we know that mechanical properties are affected by recycling because fiber length. Chain length does not affect mechanical properties because degradation is expected after so many recycling generations. The big drop in material strength throughout the recycling runs is not expected, because the bonds within the material should get more and more entangled when the material was recycled over and over again. This entanglement should replace the original strength that the material got from the intermolecular forces within the atoms of the polymeric material. Although, the decrease in forces between the chains could be seen in the elastic modulus.

In theory, mechanical properties increase with fiber inclusion resulting in better mechanical properties. Fiber inclusion reinforces material because stress is distributed between matrix and fiber material. However, fiber length and orientation is critical for effective reinforcement of a material. In this research, after 2nd recycled generation the fiber length is too short and the material behaves like a non-reinforced material. The change in mechanical properties can be described by:

∆MP = ∆FL + ∆T +∆RE +∆EN (5.1)

Where ∆MP is change in mechanical properties, ∆FL = change in fiber length, ∆CL is change in average polymeric chain length, ∆T is the change in thermal properties (e.g. crystallinity percent), ∆RE is the change or addition of re-constituents, and ∆EN = change in chain entanglement.

In this research, ∆RE = ∆EN = ∆CL =∆RE = 0 because re-constituent substances were not added to improve mechanical properties. ∆EN = 0 was assumed since it is difficult to measure and special equipment is needed. ∆T= 0 because Thermal property determination tests such as Differential Scanning Calorimetry (DSC) or Differential

Thermal Analysis (DTA) were not done.

In conclusion,

  1. Fiber length decrease during the recycling process causes loss in mechanical properties such as Ultimate tensile stress (UTS) and elasticity modulus (E).
  2. Thermoplastic material of this sort is really good to recycle due to small losses in material strength when being recycled. An optimum solution is to blend recycled plastic material with fresh plastic raw material of the same sort as the recycled material because the above decrease will be covered by the designer’s safety factor, addition of re-constituents and molding temperature.
  3. Plastic compounds contain polymer chains. The recycling process breaks some of the polymer chains, but this is usually not enough to cause material degradation.
  4. Chain length is not affected by recycling process

5.2 Recommendation

Recycled materials generally are cheaper than virgin materials and plastics producer can reduce environmental impacts. Hence, should be used in new products because is a win-win situation. This research could be improved and results and errors could be minimized if some of the following recommendations are followed:

  1. Injection molding machine should be used for the research in other to produce more standard specimens.
  2. Thermal analysis such as Differential Scanning Calorimetry (DSC) or Differential Thermal Analysis (DTA) should be performed to determine know how thermal properties with each generation.
  3. Measure additional properties like impact toughness, melt flow index, torsion stress, flexional stress, and density.
  4. Virgin polypropylene of known properties should be used for the research
  5. Run same research with different materials and common use plastics like: HDPE, LDPE, PVC, PS, PET, PC, ABS, etc.

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