Effects of styrene-acrylic emulsion doping on the properties of geopolymer wood adhesives

  Objective  Geopolymer has great research potential in wood adhesive industry due to its high mechanical properties and weather resistance. But the high brittleness and low interfacial compatibility of the inorganic network limit its bonding strength with wood. In order to increase the toughness and the shear strength, the study used geopolymer as raw material of wood adhesives to explore the application possibility of geopolymer in the field of wood adhesives and solve the harm of formaldehyde emission from wood-based panel products from the perspective of raw materials.

  Method  In this experiment, the geopolymer adhesive took styrene-acrylic emulsion as the adulterant, metakaolin (MK) as the raw material and silane (KH-550) as the coupling agent, activated by alkali and then cured to solid. Though adjusting the content of styrene-acrylic emulsion and curing process, the characteristics of geopolymer matrix and its effect on shear performance of geopolymer-based wood adhesive were obtained.

  Result  Compared with pure geopolymer, adding styrene-acrylic emulsion decreased the compressive strength and the flexural strength of the geopolymer matrix, reduced the compression-flexure ratio to 6.09, improved the shear strength to 2.6 MPa, decreased the contact angle by 4.1% as well as increased roughness of the surface of geopolymer by creating more plastic cavities and microcracks. The addition of KH-550, though decreased the compressive strength and the flexural strength, significantly promoted the modification. The compression-flexure ratio was reduced to 5.96; the shear strength was increased to 3.6 MPa; the contact angle was decreased by 25.7%; the surface’s cavities were smaller and the microstructure was more tight. The silane played a coupling role in the matrix, which makes the styrene-acrylic emulsion chemically link with the geopolymer.

  Conclusion  Styrene-acrylic emulsion organic doping and silane coupling work synergistically to form a tough film in metakaolin-based geopolymer which improves geopolymer’s brittleness and achieve a toughening effect, and to improve the interfacial compatibility of the geopolymer and wood, thus enhancing the shear strength of the geopolymer-based wood adhesive.