Effect of boron and phosphate compounds on physical, mechanical, and fire properties of wood–polypropylene composites

doi:10.1016/j.conbuildmat.2012.01.013

Construction and Building Materials

Volume 33, August 2012, Pages 63-69

https://doi.org/10.1016/j.conbuildmat.2012.01.013 Get rights and content

Abstract

Physical, mechanical, and fire properties of the injection-molded wood flour/polypropylene composites incorporated with different contents of boron compounds; borax/boric acid and zinc borate, and phosphate compounds; mono and diammonium phosphates were investigated. The effect of the coupling agent content, maleic anhydride-grafted polypropylene, on the properties of the composites with fire-retardant was also investigated. The composites with the zinc borate had the highest dimensional stability and strength in the bending, tensile, and izod impact, followed by the monoammonium phosphate, borax/boric acid, and diammonium phosphate treatments. The treatments produced modest improvements in fire performance as indicated by reductions in the heat release rates. Best results were achieved with the phosphate treatments. The Scanning Electron Microscope–Energy Dispersive Spectroscopy elemental mapping of the samples revealed that the outer surface of the wood fibers was coated by some crystalline deposits of the fire-retardants.

Highlights

► The WPCs with the zinc borate had the highest water resistance and strength values. ► Best fire performance were achieved with the phosphate treatments. ► Surface of wood fibers was coated by some crystalline deposits of fire retardants.

Introduction

Wood–plastic composites (WPCs) represent an emerging class of materials that combines favorable performance and cost attributes of both wood and thermoplastics. Lignocellulosics are increasingly applied for reinforcement in thermoplastics such as polypropylene and polyethylene due to wood’s low density, good thermal insulation and mechanical properties, reduced tool wear, unlimited availability, low price, and problem-free disposal [1]. Wood flour is the most common lignocellulosic used in WPCs. It is a commercially available material sourced from industrial residues such as planer shavings, sawdust, and wood chips and ground to a consistent mesh size. WPCs are stiffer, exhibit less creep, and are more dimensionally stable than unfilled plastic lumber.

Current growth rate of the WPC market is 22% for North America and 51% for Europe [2]. Decking for outdoor applications represent the largest market for WPCs both in North America and Europe and in both regions growth is most rapid in the decking segment [3]. WPC market share in the European decking sector is estimated to be around 6%. In Europe, total WPC production amounts to 120 thousand tons (excluding product destined for the auto industry). Around 68 thousand tons of this production is currently destined for the decking sector. The positive growth in WPC decking has led manufacturers to introduce residential construction applications include siding, roofing, windows, door frames, and outdoor furniture. Further expansion into the residential construction industry and development of applications for the furniture industry require an understanding of the fire performance of the WPCs. As organic materials, i.e. both polymers and wood, are sensitive to fire, improvement of fire retardancy of the composite materials has become important in order to comply with the safety requirements of the WPC products. Polymers employed in WPCs, burn and drip in case of fire leading to a very risky scenario. Thus, FR agents must be employed in order to improve fire behavior. The fire performance of WPCs is not well understood, and there is little information regarding the effectiveness of various FRs in the public domain.

Even though a lot of work has been reported on the fire properties of thermoplastics [4], [5], [6], [7], effect of FRs on the technological and fire properties of the wood flour reinforced thermoplastic composites only now is being more extensively investigated. The primary objective of this study was to determine effects of the boron compounds and phosphate compounds on the physical, mechanical, and fire properties of the injection molded WPCs with and without a coupling agent. The physical properties of natural fiber/polyolefin composites can be greatly enhanced by a coupling agent [8]. There is no any study related to effects of coupling agent content on the physical, mechanical, and fire properties of the WPC with FRs. The secondary objective was to investigate effect of the coupling agent content on the properties of the WPCs with FRs.

Section snippets

Materials

Wood particles were obtained from beech (Fagus orientalis Lipsky) lumbers by using laboratory type disk chipper with three knives. The moisture content of the wood particles, as determined by oven-dry weight, was found to be 40–50% prior to the treatment. The wood particles were ground in a laboratory Wiley grinder. The wood flour passing through a US 35-mesh screen was retained by a US 80-mesh. The wood flour was dried in a laboratory oven at 102 °C for 24-h to a moisture content of 0–1% based

Physical properties

The TS and WA values of the untreated and FR-treated WPC specimens without the coupling agent (MAPP) are presented in Table 2. As compared with the control specimens, the water resistance of the uncoupled specimens significantly decreased with increasing the FR content. However, the water resistance improved with the addition of the coupling agent and when the MAPP and the corresponding FR contents were increased from 2 to 4 wt.% and 4 to 8 wt.%, respectively (Table 3). The significant

Conclusions

The following general conclusions can be drawn from the study provided in the paper:

1.
Compared with the control WPCs, incorporation of the boron and phosphate compounds and the corresponding reduction in the wood flour content decreased the water resistance and mechanical properties of the uncoupled WPCs, except for the MOE. The WPCs with ZB had the highest water resistance and mechanical properties followed by the MAP, BX/BA, and DAP treatments.
2.
The use of the coupling agent (up to 4 wt.%)

Acknowledgements

This work has been supported by the Research Fund of Istanbul University, Istanbul, Turkey. Project No: 2396. Its support is gratefully acknowledged. The authors would like to thank United States Department of Agriculture, Forest Service, Forest Products Laboratory for the cone calorimetry tests.

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View full text

Effect of boron and phosphate compounds on physical, mechanical, and fire properties of wood–polypropylene composites

Abstract

Highlights

Introduction

Section snippets

Materials

Physical properties

Conclusions

Acknowledgements

Composites reinforced with cellulose based fibers

Prog Polym Sci

Wood–plastic composite lumber vs. wood decking: a comparison of performance characteristics and environmental attributes

Evaluation of various fire-retardants for use in wood flour–polyethylene composites

Polym Degrad Stabil

Flame retardant and mechanical properties of natural fibre–PP composites with magnesium hydroxide

Polym Degrad Stabil

Utilization of boron compounds as synergists with ammonium polyphosphate for flame retardant wood–polymer composites

Turk J Agric For

Effects of fire-retardants on physical, mechanical, and fire properties of flat-pressed WPCs

Eur J Wood Prod

Maleated coupling agents for natural fibre composites

Composites Part A