Atividade

Preventing Films from Marking Powder Coated Surfaces

Lignin is a natural broad-spectrum sun blocker due to its UV-absorbing functional groups, e.g., phenol units. UV absorbers can protect materials such as paints and plastic from sun damage.

Richard Venditti, North Carolina State University, Raleigh, USA, and colleagues have developed sustainable, biodegradable, and transparent cellulose-lignin films that absorb UV radiation. The team functionalized cellulose with azide groups and lignin with propargyl groups and used a copper-catalyzed click reaction to form covalent bonds between them. They added between 0.5 wt% and 2 wt% lignin to the cellulose. The team cast the solution of the bonded product onto glass plates to produce the cellulose-lignin films.

The films are transparent in the visible region of the spectrum, are flexible, and remain stable up to temperatures of 120 °C. They are prepared from renewable resources and have good UV protection properties. The material with 2 wt% lignin blocks 100 % of UV-B rays and over 90 % of UV-A rays.

Newly developed space instruments are increasingly efficient and accurate. One of the main drawbacks is that they are consequently more and more sensitive to contamination. Once integrated, optics are continuously exposed to cleanroom environment. Most of the time, cleaning operations are risky or even impossible considering coatings fragility or accessibility constraints. Thus even in cleanrooms, with the use of specific covers and/or the implementation of purging, inducing altogether stringent operational constraints, molecular and particulate contamination deposition appears to be unavoidable. Hence, the use of a windshield film on the most critical optics during manufacturing assembly and tests would allow a significant reduction of the overall contamination levels or the release of the operational constraints to reach the same cleanliness target. This study presents the results obtained in the frame of a test campaign aiming at identifying and evaluating the most promising protection films (including varnishes, adhesive tapes and electrostatic films) dedicated to space instruments optics. Impacts on both molecular and particulate contamination were investigated together with associated effects on protected substrates (aspect, spectral properties, …). The best solution has been qualified at Airbus and is currently implemented on flight hardware.