Evaluation of Polyurethane Elastomers for Encapsulation of Hydroacoustic Transducers

Abstract

Hydroacoustic transducers are devices capable of converting mechanical energy from acoustic waves into electrical energy, and vice versa, through piezoelectric elements connected to electronics that need to be protected from contact with the water. This tightness is provided by the encapsulation of the transducers with elastomers. The use of fillers and chain extenders are known to promote a barrier for water diffusion, but it would inevitably change the other properties of the elastomer. Thus, this work aims to evaluate the effects of filler and chain extender addition on the properties of polyurethane elastomers (PUR) for this application. Thermogravimetric, thermomechanical, glass‐rubber transition temperature, hardness, and dielectric loss analyses are performed. It is observed an increase in the dielectric loss, hardness, and thermal stability with the addition of mineral fillers and carbon black. The addition of chain extender promoted a greater hardness in the final elastomer, but has no measurable effects on the dielectric loss, and decreased the thermal and dimension stability with temperature. Glass‐rubber transition temperatures remain in the range from –78 to –80 °C, which is in the acceptable range for the application as encapsulants.

New Star-Shaped Polyether-Pentols (PEPOs) for Fabrication of Crosslinked Polyurethanes—Synthesis and Characterization

“…The residue after testing was 6.95%, 12.34%, and 16.59% of the original sample weight for the series PUR2, PUR3, and PUR1, respectively. The heat resistance of the investigated PURs is similar to the reported PURs based on the comparison of the main stage of degradation (2nd) [ 38 , 39 ]. In the studied series, sample PUR1 is the most thermally stable, which is the outcome of the presence of the aromatic ring in the primary diole structure.…”

“…They are a reflection of the decomposition of urethane linking within the PUR hard segments (2nd stage), leading to depolymerization of MDI-based diisocyanate. An increase in temperature allows for the further decomposition of most urethane and urea or ester bonds caused by the degradation of soft segments of the polyols (3rd stage) [ 39 ].…”

Acoustically transparent polybutadiene-based polyurethane encapsulants for deep-sea and transducers

“…However, PURs have considerably higher water permeabilities than CR and other types of acoustically transparent encapsulating rubbers. Hence, the long-term use in water would result in deteriorating electrical insulation of hydroacoustic transducers, eventually leading to hydroacoustic transducer malfunction [10,11].…”

Fabrication and characterization of novel polyurethane Encapsulant with excellent underwater acoustic transparency and hydrophobicity

“…Polyurethane possesses advantages such as adjustable curing temperature, desirable processability, superior acoustic impedance matching with seawater, excellent adhesion property, and good low temperature resistance, which can meet the basic requirements of underwater acoustic materials. [ 5–8 ] Therefore, polyurethane is regarded as the new generation of underwater acoustic materials after rubber materials. Some scholars have studied the acoustic transparency of polyurethane elastomers.…”

“…[ 10 ] The acoustic impedance of Adiprene L100 was 1.7765 × 10 6 metric Rayl, which was 16.5% lower than sea water. Maurício F. Lemos et al [ 11 ] evaluated the effect of chain extender addition on the properties of acoustically transparent polyurethane encapsulants using hydroacoustic transducers. With the increase of chain extenders, the hardness of the cured elastomer was increased while the dimension stability with temperature was decreased.…”