Polyvinyl Chloride (PVC) has proved itself to be an exceptionally versatile material due to the ability to produce it in endless forms and shapes, and its strong, wear resistant nature. The same statement can be applied to PVC fabrics, which are most commonly a combination of PVC and polyester. These fabrics are non-flammable, economical, and have a variety of applications, including tents and tarps. They possess a low thermal conductivity, however, improving their insulating capabilities could open new applications for them, especially in the structural field. Jabbari et al. (2015) performed research to lower the thermal conductivity, therefore raising the insulation power, of PVC fabrics through the incorporation of silica aerogels. These aerogels have an incredibly high insulating factor, due to their low thermal conductivity (5-100 mW/mK), and their high porosity (80-99.8%). The research team hoped to improve the performance of PVC fabrics as insulators and reduce their density to create a new material with exceptional insulation capabilities.
Figure 1. PVC fabrics are often used to create temporary structures, can function as solar shields, and are popular for use as roofs in sports stadiums.1
For this study, Jabbari et al. (2015) added an aerogel to PVC coated polyester made using PVC green plastisol. Samples were produced via the knife coating method, and varied in the amount of aerogel that they contained. The samples underwent a comprehensive analysis including density, tensile strength, thermal conductivity, and surface characteristics testing to determine whether the silica aerogels had resulted in the predicted improvements.
The Hot Disk Transient Plane Source 2500 S was used for thermal conductivity measurements of the fabric composites. The TPS 2500 S performs absolute thermal conductivity measurements between a range of 0.005 and 1000 W/mK, and can handle both isotropic and anisotropic materials. It is capable of working with solids, liquids, pastes, and powders, and is an excellent, versatile tool for academia and industry alike. The ideal experimental set-up involving fabrics layers fabric pieces on each side of a two-sided Hot Disk sensor. This layering gives enough sample on either side of the sensor to fulfil the probing depth requirements of the TPS system. Sufficient pressure is applied in order to ensure excellent thermal contact between the pieces. It is important to select the appropriate power output for the sample being tested, for samples with lower thermal conductivities such as fabrics, a low power setting should be used. Figure 2 depicts a set up that is similar to the one used in this work. Thermtest has specialized sample holders that can accurately measure the amount of pressure being exerted on the sample.
Figure 2. Example of a set-up used to measure the thermal conductivity of fabric with the Hot Disk TPS in the Thermtest lab.
Thermal Conductivity Results of Fabric Composite Testing
Values obtained by Jabbari et al. (2015) using the Hot Disk TPS 2500S revealed that the addition of silica aerogel to the PVC fabric had lowered the thermal conductivity, resulting in an increase in the insulation capabilities of the material. The sample with the largest percentage of aerogel, 4%-aerogel, had the largest thermal conductivity decrease of 26% from 205 mW/mK to 152 mW/mK. The density of the composite materials also dropped, the composite containing 3% aerogel was the lightest overall with a total density decrease of 17% from the reference. Jabbari et al. (2015) determined that the 4% aerogel addition produced the ideal composite for the applications that they were considering, despite the fact that it was denser than the 3% aerogel sample.
Jabbari et al. (2015) concluded that the addition of silica aerogel to the PVC coating of polyester fabrics resulted in a composite that was much lighter and had better insulation characteristics than the reference material. The decrease in density and thermal conductivity, in addition to an increase in hydrophobicity (an advantage for structural applications) was achieved with only a slight loss of tensile strength. The authors concluded that this is an exciting development in creating an enhanced PVC fabric for use in tents, container linings, and temporary houses due to the incredible insulation value of the material.
Note: For comprehensive results and a full discussion of this research, please follow the link to this scientific paper in the reference section.