Degradation of Plastics Used in Art and Exterior Restoration: 3D Printing

Synthetic polymers are a growing part of heritage collections, as components of modern and contemporary art and design works, as objects within 20th century social history collections, or as archival materials. Research interest and activity in this area has grown significantly over the past 20 years, as evidenced by international research projects and numerous other funded initiatives, expert conferences, and practitioner meetings. There is clearly exceptional activity and interest in this research area.

In this regard, much use is being made of so-called 3D printers, which are able to perform three-dimensional models through additive manufacturing processes (FDM), placing one layer on top of another by proceeding in cross-sections. This technique turns out to be a new tool of 21st century artistic inspiration, which includes sculptors, architects and designers, but also engineers and health professionals. (S. R. Subramaniam, 2019).

Moreover, through 3D technologies, such as scanning, it is possible to support the restorer in multiple tasks, e.g. non-contact surveys of art assets of any size; producing rigid or flexible molds and counter-molds by combining 3D printing techniques and non-contact 3D scanning; creating missing elements for integrative restoration of art assets, etc.

It is well known, however, that UV light and short wavelengths of visible light can induce photochemical processes in organic polymers, resulting in dramatic changes in polymer properties usually referred to degradation. The lifespan of materials is measured in decades, which is considerably less than that of traditional artistic and historical materials, often measured in hundreds if not thousands of years. Understanding the mechanisms of those reactions that produce degradation of polymer properties has therefore been the subject of intense research over the past 50 years. In most cases, the primary cause of property degradation is photo-oxidation, which is initiated by light irradiation. Radiation in the ultraviolet and visible is in fact the main factor in outdoor polymer aging. Heat, humidity, pollutants, mechanical stresses and biological attacks can then come into play, but in many cases the weathering process begins with a photochemical event. UV sunlight induces photochemical processes in organic materials, resulting in oxygen fixation, rearrangements, chain scissions, cross-linking, photo-coloring, and photo-bleaching. All these processes contribute to the decrease in various properties of materials, such as physical, mechanical, barrier, appearance, electrical properties….

Despite enormous efforts in developing mechanical and chemical methods to assess degradation, there are still gaps in understanding the links between chemical reactions and engineering failures in altered polymers.

The most commonly used materials are polymers and biopolymers, the most important of which are ABS and PLA, but also PET, PVA, HIPS, NYLON, and PC.

This project aims to understand if and how it is possible to use this new technique for outdoor restorations, subject to important thermo-hygrometric variations. In order to achieve this, an artificial aging setup has been set up with the aim of reproducing an outdoor environment and verifying through Raman and infrared spectroscopies, with colorimetric analysis and with mechanical analysis the aging mode, as well as the degradation rate and determine any diagnostic procedures for the preservation of polymeric materials outdoors.