Aluminum-Filled Amorphous-PET, a Composite Showing Simultaneous Increase in Modulus and Impact Resistance

Abstract

Metal-plastic composites have the potential to combine enhanced electrical and thermal conductivity with a lower density than a pure metal. The drawback has often been brittleness and low impact resistance caused by weak adhesion between the metal filler and the plastic. Based on our observation that aluminum foil sticks very strongly to poly(ethylene terephthalate) (PET) if it is used as a backing during compression moulding, this work set out to explore PET filled with a micro and a nano aluminum (Al) powder. In line with other composites using filler particles with low aspect-ratio, the tensile modulus increased somewhat with loading. However, unlike most particle composites, the strength did not decrease and most surprisingly, the Izod impact resistance increased, and in fact more than doubled with certain compositions. Thus, the Al particles acted as a toughening agent without decreasing the modulus and strength. This would be the first case where addition of a metal powder to a plastic increased the modulus and impact resistance simultaneously. The Al particles also acted as nucleating agents but it was not sufficient to make PET crystallize as fast as the injection moulding polyester, poly(butylene terephthalate) (PBT).

Amorphous Poly(ethylene terephthalate) Composites with High-Aspect Ratio Aluminium Nano Platelets

“…It is more challenging to combine good tensile strength and impact in a more rigid polymer when filled. Other works using aluminium (Al) powder in polypropylene [ 26 ] and polycarbonate [ 41 ] also reported a deterioration of tensile strength and impact resistance. Nicolais and Nicodemo reported that styrene acrylonitrile (SAN) plastic, when filled with Al and Fe powders, led to an increase in modulus but a major decrease in tensile strength and elongation-to-break [ 27 ].…”

“…In contrast, we have taken the approach to start with a metal–plastic pair which has intrinsically good adhesion, so that the mechanical properties are not impaired, knowing conductivity will follow above a certain loading. We reported that amorphous PET filled with 15 vol.% of nodular (irregular shaped) Al particles gave a raised tensile modulus of 2.1 GPa, a strength that was invariant at ~57 MPa, and an increase in the notched Izod impact resistance (from 22 J/m for amorphous PET to 51 MPa), despite the elongation-to-break dropping from 96% to 14% [ 41 ]. It is uncommon in materials to get a simultaneous increase in modulus, strength, and impact, especially when the elongation-to-break decreases.…”

“…Al powders are made by gas atomisation. Depending on the atomising gas that is used to spray the molten aluminium, the particles can have an irregular/nodular shape [ 41 ], or be spherical. For the pigment and automotive paint industry, flattened flakes are made by ball milling the spherical or the nodular powder.…”

“…Recently, Arfat et al have investigated amorphous PET filled with nodular (irregular) Al particles, and found unusual mechanical properties that suggest that the adhesion between Al and PET is intrinsically good [ 41 ]. In order to see whether this was generally true for any Al and PET, we have investigated an Al with a defined particle shape to see the effect on properties.…”

UIO-66 as Nucleating Agent on the Crystallization Behavior and Properties of Poly(Ethylene Terephthalate)

“…On the whole, such products with PET as the raw material require longer molding cycles and higher mold temperatures to be well prepared [ 5 , 6 ]. Accordingly, the improvement of the PET crystallization rate has always been a research hotspot in the application of PET to structural materials [ 7 , 8 , 9 ].…”