Forensic Engineering of Advanced Polymeric Materials-Part VII: Degradation of Biopolymer Welded Joints.

W Sikorska,O Masiuchok,G Adamus,M Kowalczuk,M Iurzhenko,H Janeczek,M Zięba,M Musioł,V Demchenko,V Talanyuk,P Chaber,J.E Puskas

doi:10.3390/polym12051167

Abstract

Welding technology may be considered as a promising processing method for the formation of packaging products from biopolymers. However, the welding processes used can change the properties of the polymer materials, especially in the region of the weld. In this contribution, the impact of the welding process on the structure and properties of biopolymer welds and their ability to undergo hydrolytic degradation will be discussed. Samples for the study were made from polylactide (PLA) and poly(3-hydroxyalkanoate) (PHA) biopolymers which were welded using two methods: ultrasonic and heated tool welding. Differential scanning calorimetry (DSC) analysis showed slight changes in the thermal properties of the samples resulting from the processing and welding method used. The results of hydrolytic degradation indicated that welds of selected biopolymers started to degrade faster than unwelded parts of the samples. The structure of degradation products at the molecular level was confirmed using mass spectrometry. It was found that hydrolysis of the PLA and PHA welds occurs via the random ester bond cleavage and leads to the formation of PLA and PHA oligomers terminated by hydroxyl and carboxyl end groups, similarly to as previously observed for unwelded PLA and PHA-based materials.

Highlights

Biodegradable polymers are the most developed class of new sustainable materials, leading to numerous technological innovations
In the 1 H-Nuclear Magnetic Resonance spectroscopy (NMR) spectra of the PLA 2 sample and its weld, Figure 1a, the presence of the signals corresponding to the protons of methyl groups at 1.56 ppm (A) and methine groups at 5.16 ppm (B), characteristic of lactide repeating units, was observed [22]
The 1 H-NMR spectra of sample PHA 3 and its weld 3W (Figure 1b) revealed the presence of the characteristic signals corresponding to the protons of methyl groups at 1.28 ppm (A), methylene groups at 2.54 (C) and methine groups at 5.26 (B)

Summary

Introduction

Biodegradable polymers are the most developed class of new sustainable materials, leading to numerous technological innovations. Polymers 2020, 12, 1167 polymer packaging materials that will be safe for human health and the environment, and to find new areas in which their unique properties can be adopted [1]. The largest market of environmentally responsible and sustainable polymer materials is the packaging industry (39%), with construction and transportation (including ground and air) being important [2]. PLA (polylactide) and PHAs (polyhydroxyalkanoates) are the most broadly tested and developed biopolymers. PLA is a biodegradable thermoplastic aliphatic polyester, whose monomer is derived from renewable resources, such as corn starch, cassava roots, starch or sugar cane [3]. The properties of PHA biopolymers vary from crystalline-brittle to soft-sticky materials depending on the chemical structure of the side aliphatic chain attached to the β-carbon [7]

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