**1. Introduction**

The accumulation of water in the form of excessive moisture within building envelopes can lead to the premature deterioration of building materials [1]. Buildings can be affected by three main sources of moisture: external moisture from precipitation or groundwater; internal moisture from occupant presence and their activities; and built-in moisture in the materials accumulated during manufacturing. Moisture movement in building wall cavities is facilitated by air currents, heat transfer and diffusion through materials. The penetration and accumulation of excessive moisture in building envelopes can lead to interstitial condensation, which can cause structural damages, mould growth, as well as damage to indoor materials. The moisture flow in building envelopes can be controlled by using barriers in walls, floors, ceiling, and roofs, thereby preventing interstitial condensation [2].

Weather barriers are membranes used in the exterior side of the wall system and act like a shell for buildings [3]. A premium, high-performance weather barrier has four beneficial and essential functions: air resistance, water resistance, durability during construction, and the right level of vapor permeability. Although the process of vapour permeability is least understood and heavily ignored, it can greatly affect the wall performance [4]. Vapor permeability is also discussed in terms of breathability of the material as its ability to allow moisture or water vapour to pass through it [5,6]. A good weather barrier is expected to resist bulk water (in liquid form) but should not necessarily block water vapour (in gas

**Citation:** Hussain, A.; Blanchet, P. Preparation of Breathable Cellulose Based Polymeric Membranes with Enhanced Water Resistance for the Building Industry. *Materials* **2021**, *14*, 4310. https://doi.org/10.3390/ ma14154310

Academic Editor: Carlos Morón Fernández

Received: 8 July 2021 Accepted: 29 July 2021 Published: 1 August 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

form) [7]. In the past, installing barriers in envelopes was not necessary as the walls had very low insulation. However, in the current scenario when the wall interior gets wet, tighter enclosures combined with high levels of thermal insulation can significantly reduce the drying potential of the wall [8]. Vapor barriers have been used with the intention to protect walls from becoming wet, however their main disadvantage is that the barrier also prevents from drying if the interior of the walls get wet [9]. Therefore, there is a need to develop a barrier with a unique structure that can specifically allow vapour to pass through but resist water entering the building wall. The most common barriers currently used in industry are non-biodegradable fossil fuel-based, which also raises the need to develop new barriers with more sustainable properties.

Bio-based materials have recently become popular in the building and construction industry due to their insulation and hygroscopic properties [10,11]. Studies have reported that using these materials in construction increases the energy efficiency of the building and provide a comfortable and healthy indoor environment [12–14]. Some bio-based materials also have the ability to absorb and release moisture with respect to changing relative humidity levels, which can reduce the load on air conditioning and have a positive impact on wellbeing of residents [15,16]. The ability of bio-based materials to capture and lock CO2 from the atmosphere during their lifetime can be highly beneficial for the environment [17]. The Quebec building code highlights that greenhouse gas emissions from buildings account for a large share of the region's overall emissions and strives to achieve its emission reduction targets by 2030 [18]. To accomplish this goal, buildings should have a highly energy efficient design as well as lower embodied energy. Since majority of the electricity generated for use in Quebec buildings is derived from hydroelectricity, which is a renewable source, the embodied energy of buildings plays a major role in contributing towards carbon emissions during their life cycle [19]. Quebec has immense potential for developing new renewable materials from wood by-products that will result in the production extremely lower embodied energy materials.

Cellulose is the most abundant organic compound, and it can be obtained quite easily from wood pulp in the form of very thin and long fibers. Recent advancements in science have supported the development of industrial processes for the extraction of cellulose fiber from wood in large-scale volumes, having a 100% yield without the use of enzymes or chemicals [20]. The fibres have unique properties such as high specific surface area, good strength and rheological properties making them a highly versatile, biodegradable, and compostable additive for a composite as either a membrane or a coating. Recent studies have used cellulose fibres for the development of films addressing mechanical [21,22] and optical properties [23,24]. However, a few studies have reported excellent vapor barrier properties in packaging applications [25–27] and their use in the construction industry [28].

Cellulose is highly hydrophilic due to the presence of hydroxyls in its chemical structure. High moisture sensitivity in bio-based materials can lead to fungal growth and compromise the durability of the material [29]. Furthermore, the quality of the end product can be affected during the manufacturing stages if cellulosic materials encounter humid environments or unexpected water [30]. The high water absorption capacity of biobased materials also makes them incompatible with hydrophobic polymers causing poor interfacial adhesion in the composites [31,32]. Numerous studies have investigated the effect of alkali [33], acetylation [34], ionic liquids and salts [35–37], silane [38], sol-gel [39], and surfactant [40,41] treatment of bio-based materials that improve their hydrophobicity and compatibility with polymers.

Cellulose fibers offer wide possibilities for new product development and the objective of this research is the utilization of commercially available cellulose fibers with a bio-based polymer for the development of a breathable vapor barrier for the construction industry. The work also involves the treatment of the cellulose fibers and an investigation of their compatibility with the polymer to determine the vapor permeability, morphology, as well as physical and thermal characteristics of the composite material.
