Accelerated Ageing

Abstract

Additive manufacturing, popularly known as 3D printing, could positively change the fabrication of façade panels. Benefits include manufacturing each façade element uniquely without the use of a mould while having the potential of integrating functions as water drainage and solar shading within the object. Recycling polymers, obtained from industrial waste, could also reduce the panel’s CO2-footprint. Despite these benefits of the self-developed pellet-extrusion XL 3D print technology, less research has been done on the feasibility of the façade panel under outdoor weather conditions. Since thermoplastic polymers are highly vulnerable to weathering factors (solar radiation, temperature and humidity), preserving their mechanical integrity under outside circumstances could be an issue.

This research aims to have a better understanding of the potential environmental risks of a 3D printed product: the Aectual façade element. First, a broadening study has been conducted, in which several potential risks were investigated. Potentials risks include the effects of wind and thermal load on the façade element and the material’s resistance against fire, thermal shock and frost. The broadening study led to an in-depth study, where the effect of ultraviolet (UV) radiation and the use of UV stabilisers on the tensile strength of a 3D printed polypropylene-based (PP) composite has been researched.

During the experimental study, 3D printed materials, in the form of tensile test samples, were accelerated aged by an indoor UV test chamber. After several exposure time intervals, exposed and unexposed samples were tested on their tensile strength. We found highly scattered data of the tensile properties of the 3D printed material and no significant influence of the UV radiation on the tensile strength between the exposed and unexposed samples. However, it is observed that the extruded material itself became brittle over time. Even at an ageing of 2088 hours (87 days), an increase in tensile modulus and a decrease in yield strain were measured. Adding UV stabilisers to the same print compound tend to accelerate the brittleness of the material over time. As mentioned, the test suffers from highly scattered results due to the to the various print qualities and sample slippage during testing. These factors led to a reduction of the characteristic tensile strength properties of the 3D printed composite as material for building applications. Conventional flat-die-extruded PP-based materials, obtained from a PP-sheets manufacturer, were tested in the same manner and confirm this conclusion.

Further material experiments were conducted to gain a better understanding of the effect 3D printing on the physical structure of the polymer-based composite. Techniques involve differential scanning calorimetry, digital and scanning electron microscopy and Fourier-transform infrared spectroscopy. The result show that the 3D printed material exhibits different polymer characterises such as the degree of crystallinity, surface structure and chemical composition compared to the raw, injection-moulded and flat-die-extruded materials.

In the discussion, the limited effect of UV degradation on the polymer’s mechanical strength is explained by several reasons, including the impact of the 3D printing itself. The conclusion includes a summary of all the findings throughout the whole research, with emphasising on the low characteristic tensile values of the 3D printed samples compared to the conventional flat-die-extruded samples. Sample slippage and inconsistent print qualities are factors contributing to this result. In the end, a list of potential improvements is given, including several techniques to further investigate the effect of 3D printing on the material properties of polymers and the development of 3D print technology for building applications.