Characteristics of the photochemical prevulcanization in a falling film photoreactor

Abstract

The photochemical prevulcanization of natural rubber (NR) latex via the thiol-ene reaction is a new approach aiming at the replacement of noxious processing agents used in conventional sulfur vulcanization processes (e.g., accelerators) together with cost saving options. The crosslinking reaction involves the excitation of a selected photoinitiator with ultraviolet (UV) light which is followed by the formation of thioether links due to the thiol-ene addition reaction. The photochemical process is carried out in a falling film photoreactor which provides not only a continuous prevulcanization process but also exhibits a technology which is already commercially well established. The main advantage of the falling film process lies in the short prevulcanization time and the mild reaction temperature. Following the idea of the manufacture of low-allergenic surgical gloves made from NR latex without compromising on the glove quality by means of physical performance, crucial process parameters of the falling film process have been determined and characterized in this study. Surgical gloves were made from the photocured NR latex which was prevulcanized using selected process conditions. The physical properties including tensile strength, elongation, modulus, and crosslink density were examined together with the aging stability and the stability against high-energy radiation (sterilization with gamma rays). It was found that the UV light intensity, the number of illumination cycles, the choice of photoinitiator, and the thiol crosslinker play an important part in the glove quality.

Dual crosslinking of carboxylated nitrile butadiene rubber latex employing the thiol‐ene photoreaction

“…It ensures short reaction times, ambient curing temperatures, and the substitution of noxious process chemicals that often elicit allergenic reactions of the human skin. As a consequence, UV crosslinked latex articles are characterized by good skin compatibilities and furthermore exhibit high tensile strengths 12–14…”

Thiol‐Ene versus Binary Thiol–Acrylate Chemistry: Material Properties and Network Characteristics of Photopolymers

“…[11][12][13] UV induced thiol-ene chemistry is also used for the synthesis of functional polymers and the side-chain modification of polymers. [18] Low field 1 H multiple-quantum (MQ) solid-state NMR experiments revealed that thiol-ene elastomer networks exhibit homogenous networks with narrow spatial crosslink distributions and a low amount of short chain defects (<5%). [14][15][16] By employing multi-functional thiols, thiol-ene chemistry can also be applied to efficiently crosslink diene-rubber materials in liquid and solid state.…”

“…[15][16][17] This new photo-vulcanization technique facilitates the crosslinking of diene-rubbers under mild conditions and short reaction times. [18] Low field 1 H multiple-quantum (MQ) solid-state NMR experiments revealed that thiol-ene elastomer networks exhibit homogenous networks with narrow spatial crosslink distributions and a low amount of short chain defects (<5%). [19][20][21] While thiol-ene chemistry is of great value in the fabrication of functional elastomers, the convenient formation of uniform polymer networks with low shrinkage stress is a sought-after property in numerous applications, ranging from dental restoratives over advanced coatings to optical materials.…”

Design of a Prototype Photoreactor UV-LEDs for Radiation Vulcanization of Natural Rubber Latex

“…The photoreactor is a vertical glass column with a diameter of 13.5 cm and a length of about 1 m, with the source of the UV-A/B radiation emitted from one UVmercury lamp type T8 TL with a length of 1 ft, power of 3000 W, and irradiance of 1.1 W/cm 2 . This lamp is located in the middle of the glass column, as shown in Figure 2 Schlögl et al, 2012;Schlögl et al, 2014). The VNRLI process is carried out as follows: A thin layer (film) NRL is passed through the photoreactor wall using gravity at a flow rate of 1.3 liters/minute and then irradiated with a beam of UV-A/B photons derived from the UV-mercury lamp irradiators.…”

“…The new technique of vulcanizing NRL with UV-A/B radiation has an advantage: it does not use a sensitizer, accelerator material such as dithiocarbamate and 2-mercapt-benzothiazole which are a high risk of cytotoxicity and tissue irritancies, or activators, so it is worth considering for further development in the manufacturing of surgical gloves Schlögl et al, 2012;Schlögl et al, 2014).…”