Preparation and characterization of fire retardant straw/magnesium cement composites with an organic-inorganic network structure

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Date: May 20, 2018
Publisher: Elsevier B.V.
Document Type: Abstract
Length: 5,911 words
Lexile Measure: 1440L

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ABSTRACT

Magnesium cement product is an excellent fire-retardant material that has been extensively used in the building materials industry. But their strength and ability to withstand humid conditions still yet to be improved. The silicone-acrylate emulsion was utilized in this study to improve the water resistance and mechanical strength of the straw-magnesium cement (SMC) composites. The properties improvement mechanism and fire-retardant performances was also analyzed. For the SMC composites containing 6% silicone-acrylate emulsion, the modulus of rupture, internal bond strength and the strength retention coefficient after immersion have all increased significantly. In contrast, the thickness swelling, water absorption decreased dramatically. The analysis results showed that an organic-inorganic network structure was formed in the novel magnesium cement, which enhanced the integrity of the material and played a role in protecting the crystals against hydrolysis. With the enhanced water resistance and mechanical strength, the novel SMC composites broadened the use in humid environments and increased the service life. Their excellent fire-resistant properties make the novel SMC composites an ideal candidate for use in public venues.

Keywords:

Straw

Magnesium cement

Silicone-acrylate emulsion

Mechanical property

Water resistance

Fire-retardant

Organic-inorganic network structure

GRAPHICAL ABSTRACT

1. Introduction

Magnesium cement was synthesised by combining lightburned magnesium oxide, magnesium chloride hexahydrate and magnesium sulphate heptahydrate [1,2]. Magnesium oxide, the main component of magnesium cement, is the first commonly used refractory oxide with a refractoriness of 2800[degrees]C. Therefore, magnesium cement products generally possess good fire and temperature retardant characteristics and are often compounded with combustible materials such as plant fiber, which has been found to withstand high temperatures above 500[degrees]C [3]. Moreover, magnesium cement can bond well with rice, corn, wheat and other crop straw [4]. Traditional polymer adhesives are difficult to bond with crop straw because of the high ash content and inorganic cuticle layer of crop straw [5]. All this makes magnesium cement as emerging cement in the wood-based panel industry and building materials industry to produce straw-magnesium cement (SMC) composites. Nowadays, SMC composites have been widely used in wall panels, fire doors, light flooring, furniture panels, construction, decorations and packaging materials [6,7].

Magnesium cement can be cured at normal temperature and pressure [8]. The cured product is largely comprised by the xMg [(OH).sub.2]yMg[Cl.sub.2] x z[H.sub.2]O, xMg[(OH).sub.2] x yMgS[O.sub.4] x z[H.sub.2]O, and with a small amount of Mg[(OH).sub.2] gels. But the 3 Mg[(OH).sub.2]Mg[Cl.sub.2]-8[H.sub.2]O (phase 3) and 5 Mg[(OH).sub.2]Mg[Cl.sub.2]-8[H.sub.2]O (phase 5) serve as the main crystalline phases [9,10], and the needle-like phase 5 is the strength phase, which means that the bonding strength of magnesium cement increases with increasing proportion of this phase [11]. However, if magnesium cement coagulate too fast, most of the heat of hydration is released within a short time, thus, the reaction heat is too concentrated during the hardening process, resulting in a low proportion of the phase 5 [12]. Moreover, the phase 3 and phase 5 crystallites would slowly hydrolyse and transform into loose, layered Mg[(OH).sub.2] crystals in a wet environment, finally forming Mg[Cl.sub.2] and other water-soluble salts [13]. The hydrolysis reaction will irreversibly...

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Source Citation   

Gale Document Number: GALE|A540211626