Influence of morphology and dispersion stability of CNC modified with ethylene oxide derivatives on mechanical properties of PLA‐based nanocomposites

Abstract

The aggregation state of cellulose nanocrystals modified with surfactants (CNC/S) in water and CNC/S powder dispersion stability in chloroform were studied and correlated with mechanical properties of nanocomposites with poly(lactic acid) (PLA). Four types of nonionic surfactants were used: PEG 300, PEG 1000, poly(ethylene glycol) monooleate, and Pluronic® L44 (PL44). The CNC/PL44 showed the smallest size of CNC aggregates dispersed in water before freeze‐drying, as determined by atomic force microscopy. The respective powder also showed the lowest decay rate of relative turbidity among CNC/S dispersions in chloroform. This, together with the improved surface coverage of CNC by PL44, verified by zeta potential (large change in the zeta potential of CNC/S dispersion in chloroform) and thermogravimetric analysis (improved thermal stability of CNC/S powder), yielded the highest tensile strength at break (TS) among PLA/CNC/S nanocomposites. Despite none of surfactants produced nanocomposites with TS higher than PLA or PLA/CNC, the aggregation state of CNC/S in water is well correlated with mechanical properties of PLA/CNC/S nanocomposites prepared by solvent casting. This correlation indicates that hornification cannot be avoided for the conditions used to prepare CNC/S powder and that there are two opposite effects in preparation of PLA/CNC/S nanocomposites. First, the effectiveness of steric barrier of nonionic surfactants against aggregation during freeze‐drying depends on complete surface coverage of CNC, together with hydration of stabilizing chain. Since hydration depends on hydrophilicity of stabilizing chain and compatibility with PLA depends on its nonpolar nature, this strategy alone seems not to be efficient to produce high‐performance nanocomposites. POLYM. COMPOS., 40:E399–E408, 2019. © 2018 Society of Plastics Engineers

A Short Review on the Effect of Surfactants on the Mechanico-Thermal Properties of Polymer Nanocomposites

“…The modification improved the maximum degradation temperature of the nanocomposites up to 0.6% compared to neat PLA [16]. This is attributed to the higher thermal stability of PEGMONO, which covered the surface of the CNCs and prevented the modified CNCs from decomposing quickly [14]. Nevertheless, the tensile strength of the nanocomposites decreased in comparison with the nanocomposite without PEGMONO; this is because of the presence of CNC/PEGMONO aggregates.…”

“…PEGMONO (chemical structure showed in Figure 2b) could modify organic nanofillers such as CNCs and modified CNCs have been utilized for the preparation of CNC/PLA nanocomposites [14]. The modification improved the maximum degradation temperature of the nanocomposites up to 0.6% compared to neat PLA [16].…”

“…Synthetic polymers (examples are displayed in Table 1) are frequently utilized for the creation of polymer nanocomposites, including HDPE [1], PP [2], PS [3,4], DGEBA [5][6][7], PEVA [8,9], PBO [10], SR [11], PAN [12], PUA [13], etc. Synthetic biodegradable polymers (examples are also displayed in Table 1), such as PLA [14][15][16][17][18], PBAT [19], PBS [20], PVA [21], PCL [22], etc., are also utilized for nanocomposite preparation. On the other hand, nanofillers (examples are displayed in Table 2), such as MMT [2,9,12,20], Ag NPs [17,18], ZnO NPs [15], TiO 2 NRs [3], CNTs [10,23,24], CNFs [5,25,26], G NPs [11,13,23], GO NSs [6,27], LDHs [22], and HNTs [4], are used in the fabrication of polymer nanocomposites, as they possess a high aspect ...…”

“…The application of bio-based nanofillers, for example, CNCs [15,18,28,29], CNPs [30], NCFs [8,19], and CNWs [7,16], also contribute to the production of nanocomposites because they are renewable and sustainable materials. Surfactants (examples are also displayed in Table 2), for instance, HTAB [13,20,31], DDAB [12,32], SDS [4,21], Ultraric PE 105 [19], Niax L-595 [8], HMAC [9], Triton X-100 [6,10,11,24], Beycostat A B09 [15,17,18,28], LAE [29], PEGMONO [14,16], Pluronic [7,14], OA [3], AK8805 [5], SA [2], PA [22], Span 60 [30], and BHHB [1], are commonly employed for modifying nanofillers in the preparation of polymer nanocomposites.…”

Shape tunability of carbonized cellulose nanocrystals

“…As reported by Buffa et al [47], the rheology of the CNCs dispersion is very sensitive to the addition of additives and polarity of the medium chosen. Room-temperature dispersion of CNCs is commonly achieved using polar solvents such as water [48], alcohols [49] or polyethers as non-ion surfactants [50]. The use of solvents during pyrolysis under pressure is a common practice to promote more homogenous reaction conditions [51].…”