Processing and compressive strengths of syntactic foams with and without fibrous reinforcements

Fabrication of water-soluble loose-fill foam from tamarind (Tamarindus indica L.) seed polysaccharide by mechanical frothing and freeze-drying process

The water-soluble loose-fill foam obtained from tamarind seed polysaccharide (TSP) was successfully prepared by a combination of mechanical frothing and freeze-drying process. The effects of TSP concentration, plasticizer content, and surfactant content on the cellular morphology, physical properties, mechanical properties, and moisture absorption were investigated. The cellular structure of TSP foam exhibited an open cell structure with a non-uniform size of the cell window, and the density varied in a range of ∼0.006–0.106 g/cm3. Foam preparation with high TSP concentration, low plasticizer as well as glycerol content enhanced the mechanical properties of the obtained foam, including tensile strength, compressive strength, and hardness. The high compressive strength of TSP foams up to ∼1.03 MPa can be produced which demonstrates that TSP foam is capable to use as a loose-fill product.

Microballoon Wall Thickness Effects on Properties of Syntactic Foams

A novel approach for changing the density of syntactic foams, while keeping the microballoon (hollow particles) volume fraction constant, is adopted in this work. This is achieved by selecting microballoons of the same size but with different wall thickness. Five types of microballoons are selected to fabricate syntactic foams. All the types of microballoons have about 40 mm mean particle sizes, but different wall thicknesses. This approach allows to maintain the same volume fractions of constituents and interfacial area while changing the density of syntactic foams. The fabricated syntactic foams are tested for their compressive properties in accordance to the ASTM D 695-96 standard. The results of the experimental investigation show a strong dependence of the compressive properties and the fracture characteristics of syntactic foams on the microballoon wall thickness. Shear cracking followed by cracking under secondary tensile stresses has been observed as the fracture mode. The present approach is found to be more effective than changing the microballoon volume fraction to change the syntactic foam density as it considerably increases the strength to the weight ratio.

Compressive Properties of Syntactic Foam Reinforced by Warp-knitted Spacer Fabric

Syntactic foam composites are widely used as aviation, construction and marine materials because of their high specific strength, specific modulus, damage tolerance and low moisture absorption. The present work aimed to investigate the compression behaviours of syntactic foam reinforced by warp knitted spacer fabric (SF-WKSF). Eight kinds of SF-WKSF samples were produced with warp knitted spacer fabrics of various surface layer structures and parameters including inclination-angle, fineness of spacer yarns, different microballoons types as well as contents. The compression tests were carried out on aMTS material testing system and the compression properties of SF-WKSF were analyzed based on the experimental compressive stress-strain curves and modulus values. It was indicated that the SF-WKSF made with preferable spacer fabric showed higher compressive modulus and yield strength values compared to neat syntactic foam (NSF). The results also demonstrated that all the parameters had significant effects on the compression performances of SF-WKSF. The composites could gain better anti-compression capacities by selecting larger inclination-angle, coarser spacer yarn, denser surface layer structure, higher microballoon density and higher S60HS microballoon contents.

Low-Density Phenolic Syntactic Foams: Processing and Properties

Low-density phenolic syntactic foams with different volume percentages of microballoons were processed and their mechanical performance has been evaluated in terms of tensile, flexural, compressive and the corresponding specific properties. Tensile and flexural strength increased with volume fraction of microballoon and optimized at 72–74 percentage by volume of microballoon. Both the properties decreased with further addition of microballoon. The corresponding specific properties also manifested a similar order. Compressive and specific compressive strength decreased with increase in microballoon volume percentage. The flexural and compressive modulus values followed the same trend as the strength values. The properties of phenolic syntactic foams were compared with syntactic foams based on an addition cure phenolic resin, Propargyl Ether Novolac resin (PN). The mechanical properties of the latter were inferior to those of phenolic syntactic foams. The morphology of the failed samples as examined by SEM showed that failure occurred by a combination of matrix and microballoon failure at low microballoon loading whereas it occurred by microballoon cracking and resin to microballoon debonding at high concentration of filler. The dynamic mechanical analysis of phenolic and PN resin syntactic foams showed a higher use temperature for PN system in comparison to phenolic.