Task 7

Develop multi-modal non-destructive testing for recycled plastics in products

Goals/Objectives

  • The goal and objectives of this task are developing a multimodal handheld device that can test the percentage of recycled plastics in the products. These methods can include not limited to:
    • Dielectric spectroscopy
    • Impedance spectroscopy
    • Photothermal spectroscopy
    • Photoacoustic spectroscopy

Methodology

Investigation of electrical properties

  • Assumption: broken bonds and other electrical defects may act as localized dipoles in recycled plastic.
  • These defect dipoles behave like lattice-defect dipoles rather than free-electron hopping affecting permittivity and dielectric loss.
  • Loss tangent δ = ϵ’/ϵ’’ of the dielectric response, where ϵ’and ϵ’’ refers to real and imaginary parts of the dielectric constant respectively.
  • Two orthogonal sets of experiments carried out:
    • Impedance spectroscopy as a function of frequency

 as a function of frequency

  • Tribo-measurement of dielectric constant – done in Kelvin probe mode

at a very low frequency

  • Results show correlations with respect to the percentage of recycled materials in the sample.
  • Permittivity is a bulk property.
  • Phase angle can be affected by surface properties. Need more experiments to determine the effects.

Investigation of optical properties

  • Assumption: Recycled plastics have more defects. The defects may change the optical properties of plastics.
  • Photothermal/photoacoustic spectroscopy method can be used to study the optical properties of the plastics. Investigation of electrical properties

Task Team Members

  • Faculty Leads: Dr. Thomas Thundat and Dr. Amit Goyal
  • Students and postdocs: Chandra Lekha Jyothula, Yaoli Zhao 

Results/Preliminary Results

  • Tribo-measurement (contact and separation mode) was performed to study the effect of recycled plastics in the PET product. The preliminary results showed that the developed method can effectively identify the PET with different percentages of recycled parts. It indicated that the defects introduced by the recycled plastics change the electrical properties of the material. 

Figure 1. Voltage output of the plastic sample containing different percentages of recycled parts under tribo-measurement (contact and separation mode) experiments.

•      Traditional Fourier transform infrared FTIR spectroscopy was carried out on PET samples with different percentage of recycled plastics with 5 scans and a resolution of 4cm-1. The IR range of this measurement is 400-4000 cm-1. Preliminary results showed that absorption bands in the recycled PET at 844, 973, and 1472 ­cm−1, are significantly weaker in recycled PET, corresponding to trans ­CH2 rocking, O–CH2, and ­CH2 bending. More specifically, they are associated with a structure derived from ethylene glycol. The literature indicated that recycling process can induce degradation including chain scission. The change in the above absorption bands indicates the elimination or modification of ethylene glycol. It is suggested that the number of the ethylene glycol group as a terminal of the polymer chain has changed. 

Figure 2. FTIR spectrum of PET with different percentages of recycled PARTS under different IR ranges. 

Ongoing/Future Work

  • Quantify the electrical properties with PET containing a specific percentage of recycled parts.
  • Quantity the optical properties with PET containing specific percentage of recycled parts.
  • Design a platform for handheld device. 

Task Alumni

  • Asalatha Nair Syamala (India)
  • Saikumar Veeraswami (North Carolina)