Thermal, Morphological and Mechanical Properties of Multifunctional Composites Based on Biodegradable Polymers/Bentonite Clay: A Review

Abstract

The extensive use of non-biodegradable plastic products has resulted in significant environmental problems caused by their accumulation in landfills and their proliferation into water bodies. Biodegradable polymers offer a potential solution to mitigate these issues through the utilization of renewable resources which are abundantly available and biodegradable, making them environmentally friendly. However, biodegradable polymers face challenges such as relatively low mechanical strength and thermal resistance, relatively inferior gas barrier properties, low processability, and economic viability. To overcome these limitations, researchers are investigating the incorporation of nanofillers, specifically bentonite clay, into biodegradable polymeric matrices. Bentonite clay is an aluminum phyllosilicate with interesting properties such as a high cation exchange capacity, a large surface area, and environmental compatibility. However, achieving complete dispersion of nanoclays in polymeric matrices remains a challenge due to these materials' hydrophilic and hydrophobic nature. Several methods are employed to prepare polymer-clay nanocomposites, including solution casting, melt extrusion, spraying, inkjet printing, and electrospinning. Biodegradable polymeric nanocomposites are versatile and promising in various industrial applications such as electromagnetic shielding, energy storage, electronics, and flexible electronics. Additionally, combining bentonite clay with other fillers such as graphene can significantly reduce production costs compared to the exclusive use of carbon nanotubes or metallic fillers in the matrix. This work reviews the development of bentonite clay-based composites with biodegradable polymers for multifunctional applications. The composition, structure, preparation methods, and characterization techniques of these nanocomposites are discussed, along with the challenges and future directions in this field.

Keywords: bentonite clay; biodegradable polymer; mechanical properties; morphological; thermal.

Figure 1

Schematic illustration of the nanocomposite structures. Three main types of morphology, including agglomerates, intercalated, and exfoliated structures of polymer-based clay nanocomposites can be obtained. Reprinted with permission from Ref. [30]. Copyright 2021, MDPI.

Figure 2

General structure schematic of bentonite clay. Reprinted with permission from Ref. [31]. Copyright 2014, Royal Society of Chemistry.

Figure 3

XRD pattern of: (a) Ca-bentonite clay. Reprinted with permission from Ref. [36]. Copyright 2020, MDPI; (b) Na-bentonite clay. Reprinted with permission from Ref. [37]. Copyright 2011, Elsevier.

Figure 4

TGA and DTG curves of the unmodified bentonite (PB) and modified bentonite (MB). Reprinted with permission from Ref. [41]. Copyright 2005, Elsevier.

Figure 5

(a) TGA curves of untreated and organically treated bentonites. (b) DTA curves of crude and organically treated bentonites. Reprinted with permission from Ref. [39]. Copyright 2010, Elsevier.

Figure 6

Schematic illustration of (a) in situ polymerization, (b) melt processing, and (c) solution casting methods for the preparation of polymer-based bentonite nanocomposite. Reprinted with permission from Ref. [42]. Copyright 2014, Royal Society of Chemistry.

Figure 7

Demonstration of the application of biodegradable polymers in different fields. Reprinted with permission from Ref. [65]. Copyright 2022, Springer Nature.

Figure 8

TEM micrographs for PLA-based bentonite nanocomposites. Low (left) and high (right) magnification TEM micrographs: (a,a′) PN2HMPEA, (b,b′) PN2HMPETA. Adapted with permission from Ref. [64]. Copyright 2019, Elsevier.

Figure 9

TEM micrographs of PLA-based bentonite nanocomposites compounded at different temperatures: (a) 180 °C and (b) 220 °C. All samples had 3 wt.-% bentonites added. Reprinted with permission from Ref. [67]. Copyright 2008, Wiley.

Figure 10

SEM micrographs of the bioplastic films (A) without bentonite, (B) 0.5 wt.-% bentonite, (C) 1 wt.-% bentonite, (D) 1.5 wt.-% bentonite, (E) 2 wt.-% bentonite, and (F) 2.5 wt.-% bentonite. Reprinted with permission from Ref. [68]. Copyright 2021, Elsevier.

Figure 11

Tensile stress–strain curves of neat PLA and PLA/clay nanocomposites with (a) 1 wt.-% and (b) 5 wt.-% of bentonite. Reprinted with permission from Ref. [72]. Copyright 2018, Elsevier.

Figure 12

(a) TGA profiles of the virgin PCL and PLC-based organo-modified bentonite nanocomposites (1, 5, and 10 wt.-% of nanofiller) and (b) SEM micrograph of the PCL–organo-modified bentonite nanocomposites (5 wt.-% of clay). The subfigure inserted in (a) shows that at 320 °C to 380 °C, the PCL-Bnt 10% composite demonstrated to be more stable than neat PCL. Reprinted with permission from Ref. [51]. Copyright 2021, Elsevier.