Durability of Biodegradable Polymer Nanocomposites

Abstract

Biodegradable polymers (BP) are often regarded as the materials of the future, which address the rising environmental concerns. The advancement of biorefineries and sustainable technologies has yielded various BP with excellent properties comparable to commodity plastics. Water resistance, high dimensional stability, processability and excellent physicochemical properties limit the reviewed materials to biodegradable polyesters and modified compositions of starch and cellulose, both known for their abundance and relatively low price. The addition of different nanofillers and preparation of polymer nanocomposites can effectively improve BP with controlled functional properties and change the rate of degradation. The lack of data on the durability of biodegradable polymer nanocomposites (BPN) has been the motivation for the current review that summarizes recent literature data on environmental ageing of BPN and the role of nanofillers, their basic engineering properties and potential applications. Various durability tests discussed thermal ageing, photo-oxidative ageing, water absorption, hygrothermal ageing and creep testing. It was discussed that incorporating nanofillers into BP could attenuate the loss of mechanical properties and improve durability. Although, in the case of poor dispersion, the addition of the nanofillers can lead to even faster degradation, depending on the structural integrity and the state of interfacial adhesion. Selected models that describe the durability performance of BPN were considered in the review. These can be applied as a practical tool to design BPN with tailored property degradationand durability.

Keywords: biodegradable polymers; biodegradation; creep; durability; environmental ageing; modelling; nanocomposites.

Figure 1

Classification of biopolymers. Reproduced with permission from [12]. Copyright © (2013). Elsevier Ltd. (licence No. 5142931044479).

Figure 2

Photos of (a) PBS; (b) 40% NFC; (c) 7/3; (d) 5/5; (e) 3/7 and (f) 40% MCC films during biodegradation studies in soil burial test conducted in composting conditions [55].

Figure 3

Basic types of durability tests for polymer composite materials.

Figure 4

Molar weight of PLA during thermo-oxidative ageing as a function of exposure temperature. Dots: experimental data used from [116]; lines: linear approximations.

Figure 5

Complex viscosity of pure PBSA and PBSA/TiO₂ nanocomposites (a) before and (b) after 360 h of UV irradiation as a function of frequency at 140 °C (reproduced from [100], copyright © (2019). Hindawi, (c) relative change of complex viscosity of PBSA filled with TiO₂ (relative weight content is indicated on the graph) vs. frequency. Dots: experimental data used from [100]; lines: approximations by logarithmic functions.

Figure 6

Kinetics of water absorption of poly(D,L-lactide) filled with cellulose nanowhiskers at different filler contents indicated on the graph. Reproduced with permission from [13]. Copyright © (2011). Elsevier Ltd. (licence No. 5135221438116).

Figure 7

Tortuosity factor as a function of filler volume fraction for PLA filled with different nanofillers (indicated in the legend).

Figure 8

Diffusion coefficient as a function of water activity for neat PBS and PBS/GnP nanocomposites [99].

Figure 9

A schematic strain vs. time curve in a creep-recovery test.

Figure 10

The (a) creep-recovery vs. time curves of starch only and starch–CNF composite films (reproduced with permission from [10], copyright © (2015), Elsevier Ltd., licence No. 5143001008321). (b) Viscoelastic and viscoplastic (ve+vp), elastic (el) and residual (res) strains of starch modified with cellulose nanofibrils vs. filler weight fraction. Dots: experimental data from [10]; lines: approximations by polynomial functions.