Mechanical properties of a rubber-reinforced block copolymer PMMA: Effect of the nanostructuration on tribological performances
Graphical abstract
Introduction
Acrylic polymers such as poly(methylmethacrylate) or PMMA, which have good optical and mechanical characteristics, have wide applications in the industrial market. Yet two major drawbacks had to be overcome. The first one is that the mechanical damage mechanisms of poly(methylmethacrylate) under stress generate the apparition of crazes [1], [2]. To enhance the mechanical strength and delay such crazes apparition, rubber-acrylic composites were developed over the past decades. An efficient method consists of small core–shell rubber particles of three hundred nanometers embedded in the acrylic matrix, called high impact acrylic materials [3], [4]. In these materials the refractive index of rubber and poly(methylmethacrylate) phases are alike in the range [−30°, 80°]. Out of this range a haze effect (lack of transparency) do not allow its use to automotive glazing when it would be a gain in weight compared to common glass. A new generation of rubber-acrylic composites with nanostructured architecture, block copolymers, emerged to solve this issue. The rubber inclusions’ scale drops from hundreds nm to tens nm [5], [6] and the ordered nanostructures allow adjustment of the mechanical properties depending on their homopolymer segments and resulting morphology [7]. Literature studies mainly focus on the effect of stress on micromechanical deformation mechanisms of bulk nanostructured polymers [8]. Yet understanding mechanisms of micro-scratches on the surface is necessary as the second drawback is the possible decrease of the transparency due to such micro-scratches accumulation from daily life. This study will link mechanical properties of the bulk of a standard cast PMMA, a high impact cast PMMA and a nanostructured cast PMMA from the last generation with their surfaces properties.
Section snippets
Material and methods
Three types of acrylic polymer sheets are provided by Altuglas® (Arkema). Standard cast sheets of poly(methylmethacrylate) are used as reference and two reinforced rubber-poly(methylmethacrylate) are compared. A high impact cast PMMA (CI30) with 300 nm core shells rubber particles inserted in the matrix [5] (Fig. 1a). A nanostructured cast PMMA (ShieldUp®) obtained by controlled radical polymerization [6]: methylmethacrylate–butylacrylate–methylmethacrylate triblock copolymers (PMMA–PBA–PMMA,
Results and discussion
Fig. 2a presents the elastic modulus as a function of temperature obtained by DMTA at 0.5 Hz for the three types of acrylic polymers. From −50 °C to 100 °C the elastic modulus is alike for PMMA and CI30, whereas it decreases by 25% for PMMA–PBA–PMMA. A softening of the elastic modulus appears due to the continuous matrix from soft (PBA) to glassy (PMMA) nano-domains (−20°<T<100 °C) [12], [13]. In addition the elastomeric phase and the structuration, rubber core–shells for CI30 and nanostructuration
Conclusion
PMMA is widely used in the glazing sector and rubber-reinforced materials were developed to improve its properties. A new nanostructured material (PMMA–PBA–PMMA) avoids the transparency decrease at high temperature compared to the last generation of rubber-reinforced material (CI30). The aim of this work was to compare their mechanical properties. Bulk studies clearly show that PMMA–PBA–PMMA is more ductile than PMMA or CI30. Surface studies shows that yielding of the contact appears at higher
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