Lecture 013.016


Buldozzer  (1967) of Alain Jacquet is a 155x125x20 cm piece of thermoformed Plexiglas (3mm) which is partially covered with acrylic paint. It was broken into three parts following a disaster. It is necessary to restore it.
A study on laser welding initiated in 2005 by Sylvie Ramel was used to study the adaptation of an industrial technique to cultural heritage issues. Laser welding has shown positive and encouraging results, but unfortunately not applicable for the piece. Only a conventional bonding has proved possible, but it must be compatible with PMMA (which is very sensitive to micro-fractures), must be durable, and reversible, without modifying the visual impact.
We therefore carried out a preliminary scientific experiment. Three protective materials to protect surfaces during bonding were tested. The Impranil DLU proved to be the most convincing. Then, we selected four adhesives applied by infiltration, either named in specific articles or provided by industry. (A thermosetting adhesive: the HXTAL Nyl-1, two adhesive crosslinks UV: Dymax 3099 and Vitralit 4731, a solvated adhesive: Plexigum PQ11)
We made flat and 3D samples of similar PMMA as the piece. We then established the evaluation criteria: – The implementation was evaluated by the absence of overhang, rapid pre-crosslinking, ease of cleaning surfaces, the homogeneity of the distribution (…) – The visibility was evaluated with the naked eye, transmitted and oblique light on black background. We observed: withdrawal, the absence of bubbling, low visibility and homogeneity of the adhesive joint (…) – The strength was evaluated by suspending a container at one end of the sample. We gradually increased the weight by pouring water continuously. The total weight was then weighed and compared. We observed the break area to determine if it was an adhesive or cohesive failure.
Due to poor optical characteristics, we discarded the Plexigum PQ611 and Vitralit 4731. The HXTAL Nyl-1 has a higher strength, but lower visual qualities than the Dymax 3099. The UV crosslinking limits visibility on the quality of bonding and little is known about its long-term effects. For safety reasons, we choose the HXTAL.
To apply the adhesive, clamping is required for proper alignment and maintenance of the three pieces, but the size of the object required us to be inventive. In order to prevent additional stress or scratches, we have developed a unique system from magnets, by isolating an adhesive plastic film and mounting it on a swivel with adjustable parts. By placing them in a regular order, we were able to arrange the pieces in a precise enough method. We checked the quality of the alignment before applying the adhesive, by using oblique light and a USB microscope. The HXTAL Nyl-1 was then applied. Once the resin cured, we were able to remove the retaining system and remove any excess glue.

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