Master's Thesis

Evaluation of the quality of polethylene terephtalate flakes for the production of food grade recycled regranulate

Final Thesis 3.51 MB

Author of thesis: Ing. Martina Snopková

Acad. year: 2022/2023

Supervisor: prof. Ing. Jiří Kučerík, Ph.D.

Reviewer: Ing. Veronika Odehnalová, Ph.D.

Abstract:

Polyethylene terephthalate (PET) is a widely used plastic, especially to produce PET bottles. However,
waste PET bottles pose an environmental risk if they are not well managed. Recycling is an appropriate
way to treat PET bottles, ideally by recycling them back into PET bottles. Nevertheless, recycling PET
into food-grade recycled PET is challenging and the resulting quality is heavily dependent on the quality
of the feedstock, i.e., the PET flakes. This thesis aimed to evaluate the quality of food-grade PET flakes
on the EU market. Although the quality of PET flakes has already been the subject of several scientific
studies, the analysis of the qualitive parameters of PET flakes has never been applied to such a large
area as is the EU market. However, extensive analysis is essential for trend mapping and possible quality
optimisation. For the analysis, material from different areas of the EU collected over a period of two
years was used. The quality assessment included the quality control methods set out in EN ISO standards
and standard operating procedures (SOPs), as well as spectrophotometry, Fourier-transform infrared
spectroscopy – Attenuated total reflection (FTIR-ATR), and measurement of intrinsic viscosity. The
suitability of each supplier and trends across the batches delivered were assessed. The most important
findings included (1) other plastics content is the most problematic quality parameter of PET flakes,
(2) other plastics content originates mainly from bottles and is independent of the collection system,
(3) a higher degradation rate of PET flakes supplied by Western producers compared to the material
from producers located in the East of the EU. A comprehensive analysis of the EU market and quality
trends in PET bottle recycling by geographical area and type of collection system were provided. These
results will not only be useful for practice, but they could also provide an incentive to improve legislation
on the assessment of plastic contaminants or the introduction of more appropriate PET bottle design.

Keywords:

PET recycling, food-grade rPET, contamination, quality, PET flakes

Date of defence

23.05.2023

Result of the defence

Defended (thesis was successfully defended)

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Grading

A

Process of defence

The student presented the most significant results of her thesis. Afterwards, the reports by the thesis advisor and the thesis reviewer were presented. This was followed by two additional questions from the reviewer. Both questions were answered in detail and to the reviewer’s satisfaction. The discussion on the thesis followed. Members of the committee asked for example the following questions: What was the diameter of the sampling device? How many contaminants did you find in your samples? How did you evaluate what polymer you found? Can you describe in more detail the measurement principles behind FTIR? What other analytical methods could you use to characterize the quality of your plastics? During the discussion, the student demonstrated excellent knowledge of the subject, and she answered all questions asked by the committee without hesitation.

Language of thesis

English

Faculty

Fakulta chemická

Department

Institute of Chemistry and Technology of Environmental Protection

Study programme

Environmental Sciences and Engineering (NPAP_ENVI)

Composition of Committee

doc. Mgr. Renata Komendová, Ph.D. (člen)
doc. MVDr. Helena Zlámalová Gargošová, Ph.D. (člen)
prof. Ing. Tomáš Svěrák, CSc. (člen)
prof. Ing. Jiří Kučerík, Ph.D. (předseda)
doc. Mgr. Michaela Vašinová Galiová, Ph.D. (místopředseda)
dr. Maximilian Meyer (RPTU Kaiserslautern-Landau) (člen)
dr. Zacharias Steinmetz (RPTU Kaiserslautern-Landau) (člen)

Supervisor’s report
prof. Ing. Jiří Kučerík, Ph.D.

The submitted diploma thesis "Evaluation of the quality of polethylene terephtalate flakes for the production of food grade recycled regranulate” addresses the problems associated with mechanical recycling of PET and upgrading it to a food-grade quality. In particular, the quality of the “raw material” i.e. PET flakes is variable, which can influence both recycling chain and the quality of the PET regranulate. Mrs. Martina Snopková approached the problem methodically by testing the quality of the flakes from various providers from different parts of Europe, from countries differing in the collection systems. The obtained data are unique and applicable for improvements (both technological and legislative) of the PET mechanical recycling system. 
Mrs. Martina Snopková has been working on her diploma thesis since the 4th year, which is reflected in the amount of experimental data and variability of tested approaches.  She presented the results of her research on 90 pages of her diploma thesis, she evaluated the obtained data in a readable, careful, and often original way. Although the subject of the thesis is more technological then fundamental, she worked very well with literary sources (a total of 143 relevant citations). Therefore, it can be stated that the assignment of the work was fulfilled. I would also like to highlight diligence and patience in the elaboration of the work, independence and innovative approach to evaluation. Last but not least, it can be mentioned that the student frequently consulted her data with supervisor and mainly with the consultant and always managed to use it maximally. For this reason, my evaluation of the work is very positive resulting in an overall grade of "A".
Evaluation criteria Grade
Splnění požadavků zadání A
Studium literatury a její zpracování A
Využití poznatků z literatury A
Kvalita zpracování výsledků A
Interpretace výsledků, jejich diskuse A
Závěry práce a jejich formulace A
Využívání konzultací při řešení práce A
Celkový přístup k řešení úkolů A

Grade proposed by supervisor: A

Reviewer’s report
Ing. Veronika Odehnalová, Ph.D.

The diploma thesis by Bc. Martina Snopková addresses the issue of the quality of PET flakes from a total of 18 suppliers from different EU countries, which are intended for recycling and subsequent production of PET bottles. The chosen topic is highly relevant due to EU regulations regarding the content of recyclates in PET bottles, and the thesis provides a valuable overview of the European market that has not been conducted before.
In the theoretical part, the student showed an overview not only in the research articles on the subject but also in relevant legislation, and thanks to the collaboration with companies in the field since her bachelor's thesis, there is also evident insight into industrial practice in the text. The experimental part consists of approximately 40 pages and includes a brief description of the methods used, obtained results, and a discussion of individual analyses (entrance quality control, spectrophotometry, viscosity measurement, and contamination) conducted on up to 158 batches of PET flakes. My only objection is that it is unclear from the thesis which experiments were performed directly by the student and by the lab technicians mentioned in the text. For each studied parameter, basic descriptive statistics, a thorough discussion of the results, and recommendations/non-recommendations of individual PET flake suppliers are provided. The student also relates the results to the geographic location of the supplier (east/west) and the local type of PET bottle collection (mono/collective), which is a topic continuously discussed in the Czech Republic. The thesis includes innovative approaches to the PET flake quality analysis, such as using the lightness parameter L* instead of visual evaluation and viscosity measurement using a capillary rheometer. All observed trends are verified at the end by correlation analysis.

The thesis has a total of 90 pages, is clearly divided into four chapters, and is highly above average in terms of citations, with a total of 143 references to scientific articles, standards, and other relevant sources. It is written in English, without apparent grammatical errors, and is very readable. The thesis fulfils the assignment, and I recommend it for defence.
Evaluation criteria Grade
Splnění požadavků zadání A
Logické členění práce A
Kvalita zpracování výsledků B
Interpretace výsledků, jejich diskuse A
Využití literatury a její citace A
Úroveň jazykového zpracování A
Formální úroveň práce – celkový dojem A
Závěry práce a jejich formulace A
Topics for thesis defence:
  1. What is the average weight of a batch of PET flakes provided by the supplier, and how did you perform sampling for analysis?
  2. What parameters are traditionally obtained from measurements using plastometer, and how are they related to intrinsic viscosity?

Grade proposed by reviewer: A

Responsibility: Mgr. et Mgr. Hana Odstrčilová