Al2Mo3O12/polyethylene composites with reduced coefficient of thermal expansion

Abstract

Recently, polymer composites reinforced with low fractions of thermomiotic nanoceramics have triggered a lot of research. The efforts have been focused on achieving considerable reduction of the coefficient of thermal expansion (CTE) of polymeric materials without deterioration of other physical properties. In this context, polyethylene (PE) composites reinforced with different loads of Al 2 Mo 3 O 12 nanofillers (0.5-4 mass %) were fabricated by micro-compounding. To enhance the interfacial interaction between the two components, chemical functionalization of Al 2 Mo 3 O 12 was performed with vinyltrimethoxysilane (VTMS) prior to micro-compounding. Infrared spectroscopy and thermogravimetry demonstrated the successful grafting of VTMS on the Al 2 Mo 3 O 12 surface. The composites showed strongly decreased CTEs, up to 46 % reduction for loadings of 4 mass % compared with neat PE, suggesting intimate filler-matrix interactions. The variation of CTEs of the composites in terms of the filler fraction was successfully described by Turner's model allowing calculation of the bulk modulus of monoclinic Al 2 Mo 3 O 12 (13.6 ± 2.6 GPa), in agreement with the value obtained by an ultrasonic method. The thermal stability of the composites was improved, although the addition of functionalized fillers decreased the degree of crystallinity of the PE to a small extent. The Young's modulus and yield strength of the composites increased from 6.6 to 19.1 % and 4.0-6.0 %, respectively, supporting the existence of strong filler-matrix interactions, contributing to an efficient load transfer. Finite element analysis of thermal stresses Electronic supplementary material The online version of this article (

Effects of low contents of A2M3O12 submicronic thermomiotic‐like fillers on thermal expansion and mechanical properties of HDPE‐based composites

“…Since crystalline regions expand less than amorphous parts, this improvement in crystallinity of the matrix should contribute to reduce the CTE of polymer composites. However, the CTE of polymer composites can also be decreased when the crystallinity degree of the matrix is un‐changed or even reduced (by steric hindrance effect of fillers on chain ordering), as reported by Soares et al for medium density PE/Al 2 Mo 3 O 12 composites, where X c decreased in the range of 1.3–7.9% for 0.1–1.1 vol.% of filler. The reduction in CTE of these composites was in the range of 7.4 and 46.3% for the temperature interval of 25–100°C.…”

“…HDPE/Y 2 W 3 O 12 composites displayed larger increments in Young's modulus of ∼11 and 32% for volume fractions of filler of 0.003 and 0.011, respectively. It is important to point out that the extent of increase in Young's moduli of HDPE/Al 2 W 3 O 12 composites is in the range reported for analogous medium density polyethylene/Al 2 Mo 3 O 12 composites (6.6–19.1%) at the same filler volume fractions, but the surface of Al 2 Mo 3 O 12 fillers was treated with a silane coupling agent. On the other hand, bearing in mind polyimide composites reinforced with pristine ZrW 2 O 8 nanoparticles at filler loadings of 10 vol.%, Young's moduli of those composites increased 14% with respect to virgin matrix .…”

“…b. It is worth noting that in medium density polyethylene composites filled with Al 2 Mo 3 O 12 silanized nanoparticles experimental CTE values were fitted using Turner's approach in the temperature range of 25–100°C . For volume percentages of Al 2 Mo 3 O 12 silanized nanoparticles of 0.3, 0.6, and 1.1%, the CTE of composites dropped 7, 21, and 46%, respectively, when compared with that of the neat matrix .…”

“…It is worth noting that in medium density polyethylene composites filled with Al 2 Mo 3 O 12 silanized nanoparticles experimental CTE values were fitted using Turner's approach in the temperature range of 25–100°C . For volume percentages of Al 2 Mo 3 O 12 silanized nanoparticles of 0.3, 0.6, and 1.1%, the CTE of composites dropped 7, 21, and 46%, respectively, when compared with that of the neat matrix . The extent of CTE reductions for the same volume fractions of filler and temperature range was greater for HDPE/Y 2 W 3 O 12 (see Table ), with the exception of 1.1 vol.% of filler loading, which suggests that it is more difficult to achieve a homogeneous dispersion of Y 2 W 3 O 12 within HDPE matrix for filler contents higher than 0.6 vol.%.…”

“…This may be a consequence of better dispersion in Y 2 W 3 O 12 powder due to a different synthesis method and lower calcination temperature in comparison to Al 2 W 3 O 12 . Another important factor that should be taken into account to attain strong reductions on CTE of composites is the filler‐matrix interactions at the interface of these two components . Since Y 2 W 3 O 12 and Al 2 W 3 O 12 fillers were not surface treated, the interfacial bonding between fillers and matrix is merely due to mechanical interlocking (physical entanglements) because of the surface roughness of fillers.…”