Composites with surface-grafted cellulose nanocrystals (CNC)

Abstract

Hydroxyazetidinium salts were used to surface-modify cellulose nanocrystals (CNC) by grafting the salts onto the sulphate ester groups on the CNC surfaces. The grafting was confirmed by f-potential measurements and by the thermal degradation behaviour of the modified CNC. The thermal stability (onset of degradation) of the CNC was improved by the surface modification (almost 100°C). Composites containing surface-modified or unmodified CNC (0.1, 1.0 and 10 wt%) with an ethylene-based copolymer as matrix were produced by compression moulding. The thermal stability of the composites was not, however, markedly improved by the surface grafting onto the CNC. It is suggested that this is due to a degrafting mechanism, associated with the alkaline character of the system, taking place at high temperatures. Model experiments indicated, however, that this did not occur at the conditions under which the composites were produced. Furthermore, in the case of a reference based on pH-neutralised polymeric system and modified CNC, an upward shift in the onset of thermal degradation of the composite was observed. The addition of the CNC to the polymer matrix had a strong influence of the mechanical performance. For example, the tensile modulus increased approximately three times for some systems when adding 10 wt% CNC. The surface grafting of the hydroxyazetidinium salts appeared mainly to affect, in a positive sense, the yield behaviour and ductility of the composites. The results of the mechanical testing are discussed in terms of interactions between the grafted units and the matrix material and between the grafted groups.

Molybdenum disulphide—A traditional external lubricant that shows interesting interphase properties in pulp‐based composites

“…The addition of either TMP or DP leads to a steeper slope of the tan δ with increasing strain amplitude indicating a weaker interphase due to a poor adhesion between the phases that promotes friction losses during the imposed sinusoidal deformation. [29,30] The TMPbased composites exhibited a better interphase region up to 50 wt% loading comparable to some extent with the tensile properties given in Table 2. At higher TMP contents, the smaller proportion of EAA resulted in a poorer interphase region and greater increase in the slope of tan δ with increased strain amplitude.…”

“…The variation of the mechanical loss factor (tan δ) relative to the loss factor of the matrix with increasing strain amplitude can be used to assess the adhesion between matrix and reinforcement in terms of the presence of an interphase. [29] The dynamic-mechanical properties were measured using a Rheometrics RSA II at room temperature (25 C) at a frequency of 1 Hz, using a procedure similar to that used by Forsgren et al, [30] where the samples were pre-strained in tension by about 0.15% which was kept constant during the measurements and subjected to a sinusoidal deformation with a strain amplitude which was increased from about 0.009% to 0.14%.…”

Water‐assisted melt processing of cellulose biocomposites with poly(ε‐caprolactone) or poly(ethylene‐acrylic acid) for the production of carton screw caps

“…The mechanical loss factor (tan δ) was used as a measure of the relative strength of the interphase region between the matrix and the reinforcement. 17…”

“…Poly(ethylene-co-acrylic acid) (EAA) is a copolymer commonly used in the packaging industry, containing acrylic acid groups, providing good adhesion with a hydrophilic reinforcement. 10,[16][17][18] As biodegradable alternative to EAA, poly(ε-caprolactone) (PCL) was selected considering its biodegradability, high ductility, and toughness, but with a relatively more hydrophobic surface than the EAA. 19 Both matrices have relatively low melting points thus enabling more effective water-assisted extrusion and the possibility of low processing temperatures, which are beneficial to prevent cellulose degradation.…”

Melt Processing of Ethylene‐Acrylic Acid Copolymer Composites Reinforced with Nanocellulose

“…The addition of reinforcement to EAA7 had a negligible effect on the crystallinity of the composite, see Fig. a, as has been reported for other EAA‐based nanocellulose composites []. Thus, the improvement in the mechanical properties can be associated with the presence of nanocellulose reinforcements rather than with changes in the crystallinity of the composites.…”