Desiccant Films Made of Low-Density Polyethylene with Dispersed Silica Gel—Water Vapor Absorption, Permeability (H2O, N2, O2, CO2), and Mechanical Properties

Abstract

Silica gel is a well-known desiccant. Through dispersion of silica gel in a polymer, films can be made that absorb and desorb water vapor. The water vapor absorption becomes reversible by exposing such films to a water vapor pressure below that of the water vapor pressure during absorption, or by heating the film. The intention of this study was to achieve a better understanding about the water vapor absorption, permeability (H2O, N2, O2, CO2), and mechanical properties of films with dispersed silica gel. Low-density polyethylene (PE-LD) monolayer films with a nominal silica gel concentration of 0.2, 0.4, and 0.6 g dispersed silica gel per 1 g film (PE-LD) were prepared and they absorbed up to 0.08 g water vapor per 1 g of film. The water vapor absorption as a function of time was described by using effective diffusion coefficients. The steady state (effective) water vapor permeation coefficients of the films with dispersed silica gel were a factor of 2 to 14 (8.4 to 60.2·10−12 mg·cm·(cm²·s·Pa)−1, 23 °C) higher than for pure PE-LD films (4.3·10−12 mg·cm·(cm²·s·Pa)−1, 23 °C). On the other hand, the steady state gas permeabilities for N2, O2, and CO2 were reduced to around one-third of the pure PE-LD films. An important result is that (effective) water vapor permeation coefficients calculated from results of sorption and measured by permeation experiments yielded similar values. It has been found that it is possible to describe the sorption and diffusion behavior of water by knowing the permeability coefficient and the sorption capacity of the film (Peff.≈Seff.·Deff.). The tensile stress changed only slightly (values between 10 and 14 N mm−²), while the tensile strain at break was reduced with higher nominal silica gel concentration from 318 length-% (pure PE-LD film) to 5 length-% (PE-LD with 0.6 g dispersed silica gel per 1 g film).

Performance of an Adsorptive Heat-Moisture Regenerator Based on Silica Gel–Sodium Sulphate

“…The most efficient adsorbent for inflow air heating is apparently the composite containing 80% sodium sulphate and 20% silica gel, providing appr. six times higher adsorption capacity than the low density polyethylene-silica gel composite adsorbent gel [20], four times higher than pulp coated with silica gel [22], twice that of the glass fibre-based composite adsorbent reported by Luo et al [21] and 50% to 100% higher capacity than the sulphonic acid-modified silica investigated by Chen et al [27]. The mass and volume of silica gel-sodium sulphate composite required to supply the calculated thermal load are estimated to be 96.5 kg and 0.134 m 3 , respectively.…”

“…The most promising of them are materials obtained using the sol-gel method [19]. Other intensely studied adsorbents include various composite materials [20][21][22] containing plastics, metals or even pulp. They can be further integrated with membrane-based systems [21,23] to improve their performance and used with various air conditioning unit layouts including solar collectors [24] and heat pumps [25].…”

Water Vapor Transport Properties of Polyurethane Films for Packaging of Respiring Foods

“…The effective sorption coefficients (S eff ) were calculated using the mass fraction of water in the films (Fig. 4), the density of the films (Table 1), and the water vapor saturation pressure of 28.08 mbar (2808 Pa) at 23°C [26]. Figure 6 shows changes in S eff values for the film samples against RH.…”

“…At RH 0➔97% also showed similar results except for PU1500-50-40. A variability of the permeability by a factor of two was common for polymers of same specification or type [26]. In high RH cases especially at range of RH 0➔85%, the non-steady-state (sorption) method deviated by max up to factor 8 from the WVP values of steady- state (permeation) method especially if the PU films were not conditioned at 50% RH prior to test.…”

Reversible Hydration Composite Films for Evaporative Perspiration Control and Heat Stress Management

“…Moisture‐absorbing aerogels like carbon aerogel [ 23 ] and SiO 2 aerogel [ 24 ] are light in weight, but their bulky size and inflexibility limit their applications in PPE. The previously reported desiccant films made of polyethylene with dispersed silica gel can only achieve a maximum water uptake of 156.2 g m –2 , [ 25 ] which is less satisfactory in terms of moisture absorption capability. Hence, to maximize the cooling effect in the presence of practical constraints, our synthesized composite film has the following features: 1) fast absorption rate and high absorption capacity; 2) excellent mechanical properties; 3) low‐cost, light‐weight, and reusable.…”