Abstract
Lightweight lignocellulosic fibrous materials (LLFMs) offer a sustainable and biodegradable alternative in many applications. Enthusiastic interest in these materials has recently grown together with the newly risen interest in foam forming. Foam bubbles restrain fiber flocculation, and foam formed structures have high uniformity. Moreover, the bubbles support the fibrous structure during manufacturing enabling the formation of highly porous structures. Mechanical pressure cannot be applied in the manufacture of LLFMs as the materials would lose their porous structure. Water is therefore typically removed by a combination of drainage and thermal drying. Thermal drying of porous materials has been studied intensively. However, there are only a few studies on the drainage of fiber-laden foams. Thus, in this work, we conducted a systematic analysis of this topic. Our findings show that after drainage a stationary vertical moisture profile similar to that of pure foams is developed. Raising the initial fiber consistency was found to increase the final fiber consistency of the foam until the drainage ceased. Increasing mold height was found to increase the final consistency considerably. Without vacuum and heating, the shrinkage of samples during drainage was only slightly higher than the volume of the drained water. Drainage rate and final consistency increased clearly with increasing vacuum, but simultaneously sample shrinkage increased considerably. The best compromise was obtained with a vacuum of 0.5 kPa, which increased the final consistency by 60% without extra shrinkage. Using warm foam and heating the foam during drainage increased the final consistency considerably, but this also led to significant shrinkage of the sample.
Highlights
Lightweight lignocellulosic fibrous materials (LLFMs) offer a sustainable and biodegradable alternative in many applications such as thermal insulation (Pohler et al 2017), sound insulation (Nechita and Nastac 2018; Debeleac et al 2019), interior decoration (Harkasalmi et al 2017; Siljander et al 2019), polymer-impregnated composites, and packaging (Satyanarayana et al 2009; Huber et al 2012)
The best compromise was obtained with a vacuum of 0.5 kPa, which increased the final consistency by 60% without extra shrinkage
Using warm foam and heating the foam during drainage increased the final consistency considerably, but this led to significant shrinkage of the sample
Summary
Lightweight lignocellulosic fibrous materials (LLFMs) offer a sustainable and biodegradable alternative in many applications such as thermal insulation (Pohler et al 2017), sound insulation (Nechita and Nastac 2018; Debeleac et al 2019), interior decoration (Harkasalmi et al 2017; Siljander et al 2019), polymer-impregnated composites, and packaging (Satyanarayana et al 2009; Huber et al 2012). As lignocellulosic fibers have strong aggregation tendency, LLFMs are difficult to produce with conventional water forming. Due to the recent resurgence of foam forming, interest in these materials is growing rapidly. The bubbles restrain flocculation in the foam, and the formed structures obtain much better uniformity than achieved with water. Much higher consistencies can be used with foam when compared to water, which gives improved energy and water efficiency
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