Thermal and Mechanical Properties of Silica–Lignin/Polylactide Composites Subjected to Biodegradation

Abstract

In this paper, silica–lignin hybrid materials were used as fillers for a polylactide (PLA) matrix. In order to simulate biodegradation, PLA/hybrid filler composite films were kept in soil of neutral pH for six months. Differential scanning calorimetry (DSC) allowed analysis of nonisothermal crystallization behavior of composites, thermal analysis provided information about their thermal stability, and scanning electron microscopy (SEM) was applied to define morphology of films. The influence of biodegradation was also investigated in terms of changes in mechanical properties and color of samples. It was found that application of silica–lignin hybrids as fillers for PLA matrix may be interesting not only in terms of increasing thermal stability, but also controlled biodegradation. To the best knowledge of the authors, this is the first publication regarding biodegradation of PLA composites loaded with silica–lignin hybrid fillers.

Functional MgO–Lignin Hybrids and Their Application as Fillers for Polypropylene Composites

“…On this basis, it was observed a significant influence of the composition of hybrid filler on the thermal stability of the final system. Similar observations can be found in the available literature [14,[17][18][19]. the thermal stability of MgO depends on the type and concentration of reagents used for its production, the methodology used for its preparation and the duration of the reaction [23,24].…”

“…A crucial conclusion which can be established based on the analysis of spectra for hybrid systems is that the intensity of the bands of groups characteristic for lignin decreases with the decreasing ratio of the biopolymer in relation to the inorganic matrix. This has already been observed in our earlier reports in which SiO 2 -lignin [11,13,15,[17][18][19] or ZnO-lignin [14] hybrid materials were used. In each case, there was a permanent connection between the components, as a result of which hybrid materials belonging to the first class (with physical connection of components, mainly through hydrogen bonds) [14,[17][18][19] or the second class (chemical combination of components with the formation of covalent bonds) were obtained, depending on the method used [13,15].…”

“…This has already been observed in our earlier reports in which SiO 2 -lignin [11,13,15,[17][18][19] or ZnO-lignin [14] hybrid materials were used. In each case, there was a permanent connection between the components, as a result of which hybrid materials belonging to the first class (with physical connection of components, mainly through hydrogen bonds) [14,[17][18][19] or the second class (chemical combination of components with the formation of covalent bonds) were obtained, depending on the method used [13,15]. In the chemical method, it was important to modify the inorganic matrix properly and activate the biopolymer, which was mainly obtained by oxidation with inorganic compounds [13,15] or, alternatively, with ionic liquids [20].…”

“…Moreover, this biopolymer is distinguished from other products by properties such as biodegradability, antioxidant and antibacterial activity [10,11], good chemical reactivity [12], affinity to inorganic oxides [13,14] or possible sorption of harmful compounds from the environment due to the diversity of functional groups in the lignin structure [15,16]. These properties allow the use of lignin in the preparation of functional hybrid materials with applications as fillers for polymer composites [14,[17][18][19] or effective sorbents of environmentally harmful metal ions [15,16]. It is worth emphasizing that lignin is a renewable raw material, i.e., it corresponds well Molecules 2020, 25 with global environmental trends.…”

“…However, a significant disadvantage of lignin is its limited thermal stability. At temperatures above~200 • C this biopolymer is gradually decomposed, which ultimately results in its degradation [14,[17][18][19]. Therefore, it seems important to combine lignin with inorganic compounds, including highly thermally stable MgO [20,21].…”