High-Consistency Foam Pilot Process for Producing Fibrous Cushion Material.

High-consistency (HC) suspensions containing several weight% of fibers have been studied in the past but mainly in relation to water-laid web-forming technology. The severe flocking problems deteriorating web quality can be partly solved by using aqueous foam as a transfer medium instead of water. The processability of highly viscous HC foam and its potential to produce low-density fiber products are revealed only in large-scale dynamic conditions with the proper flow properties of the foam. For this reason, a pilot-scale study was conducted at 10-14% fiber consistency and a 3 m/min web speed using softwood, hardwood, and a 50/50 fiber mixture as raw materials. To better understand the effects of additives on foam processability and the strength of the final product, the following additives were selected: guar gum (GG), carboxymethyl cellulose (CMC), citric acid, and a combination of the latter two. These studies were supported by rheological measurements and X-ray microtomography analysis of the product structures. In rheological measurements, the HC fiber foams turned out to have significant elasticity with a high storage modulus. Interestingly, the highest consistency in the pilot studies led to the smallest mean floc size and total floc volume in the corresponding samples. The best strength properties were gained with citric acid and CMC. Overall, the findings indicate that HC foam demonstrates significant technological potential for producing sustainable fiber products with efficient water usage.