Abstract
This work examined teakwood and parawood in wood/poly(vinyl chloride) composite (WPVC) materials under UV-weathering and seawater immersion. The mechanical properties as well as anti-fungal and anti-algal performance were considered. Teakwood and parawood (a rubberwood product) in WPVC materials at ratios of 0:100, 20:80, 40:60, 50:50, 60:40, 80:20, and 100:0 were investigated. UV-weathering ageing periods of 0 to 32 days and seawater immersion periods of 0 to 90 were studied. Aspergillus niger TISTR 3012 and Chlorella vulgaris TISTR 8580 were used as marine fungi and marine algae, respectively. Higher parawood content (in formulations of 0:100, 20:80 and 40:60) in WPVC composite materials enabled better mechanical properties than those of higher teakwood content (in formulations of 60:40, 80:20 and 100:0). Seawater immersion caused more deterioration of WPVC composite materials than UV-weathering ageing. Both anti-microbial agents and wood particles are potentially used in WPVC composite materials for anti-microbial properties, including the percentage reduction of fungal and algal growth. Increasing UV-weathering ageing and seawater immersion periods decreased the percentage reduction of fungal growth, but increased the percentage reduction of algal growth in WPVC composite materials. The results suggested higher parawood content (in a formulation of 20:80) for WPVC composite materials for coastal environment applications.
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Mechanical Performance and Anti-Fungal and Anti-Algal Properties for Teakwood/Parawood/PVC Composites in UV-Weathering and Seawater Immersion Conditions
Sirichai Kanking,a Tawich Pulngern,b Vichai Rosarpitak,c and Narongrit Sombatsompop a,*
This work examined teakwood and parawood in wood/poly(vinyl chloride) composite (WPVC) materials under UV-weathering and seawater immersion. The mechanical properties as well as anti-fungal and anti-algal performance were considered. Teakwood and parawood (a rubberwood product) in WPVC materials at ratios of 0:100, 20:80, 40:60, 50:50, 60:40, 80:20, and 100:0 were investigated. UV-weathering ageing periods of 0 to 32 days and seawater immersion periods of 0 to 90 were studied. Aspergillus niger TISTR 3012 and Chlorella vulgaris TISTR 8580 were used as marine fungi and marine algae, respectively. Higher parawood content (in formulations of 0:100, 20:80 and 40:60) in WPVC composite materials enabled better mechanical properties than those of higher teakwood content (in formulations of 60:40, 80:20 and 100:0). Seawater immersion caused more deterioration of WPVC composite materials than UV-weathering ageing. Both anti-microbial agents and wood particles are potentially used in WPVC composite materials for anti-microbial properties, including the percentage reduction of fungal and algal growth. Increasing UV-weathering ageing and seawater immersion periods decreased the percentage reduction of fungal growth, but increased the percentage reduction of algal growth in WPVC composite materials. The results suggested higher parawood content (in a formulation of 20:80) for WPVC composite materials for coastal environment applications.
DOI: 10.15376/biores.18.3.5599-5622
Keywords: UV; Seawater; Mechanical properties; Anti-microbial properties; Teakwood; Parawood; Wood/poly(vinyl chloride) composite
Contact information: a: Polymer PROcessing and Flow (P-PROF) Research Group, Materials Technology Programme, School of Energy, Environment and Materials, King Mongkut’s University of Technology Thonburi (KMUTT), 126 Pracha-Uthit, Bangmod, Thungkru, Bangkok, 10140, Thailand; b: Department of Civil Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi (KMUTT), 126 Pracha-Uthit, Bangmod, Thungkru, Bangkok, 10140, Thailand; c: V.P. Wood Co., Ltd., 72/1 Moo. 4, Suksawat 41, Banphueng, Phra Pradaeng, Samut Prakan, 10130, Thailand;
* Corresponding author: narongrit.som@kmutt.ac.th
INTRODUCTION
Coastal environments are located at the interface between the land and sea, which are comprised of coastal land and aquatic systems including islands, salt marshes, wetlands, beaches, rivers and estuaries, and transitional and intertidal areas (Crossland et al. 2005). Important parameters that influence the structure and appearance of sea-adjacent or marine accommodations include the wind, both land and sea breezes, UV light, seawater, transitional and intertidal behaviours, and micro-organisms.
An artificial wood used in modern houses and living constructions has become interesting in terms of being lightweight and having easy moulding and bending, easy installation and uninstallation, and a nature-like appearance. Wood/poly(vinyl chloride) composite (WPVC) has been considered for strengthening structural applications. It was found that the addition of wood flour in WPVC materials increased the flexural modulus and strength by up to 40 phr, while hardness was not affected (Jeamtrakull et al. 2012). Increasing the web thickness and decreasing the flange spacing of the log-wall panels resulted in an increment of ultimate load by 3.6 times and 2.3 times, respectively, but the ultimate load decreased by 4.8 times when increasing the slenderness ratio (Pulngern et al. 2017). Loading for the edge-wise direction in WPVC composite provided high flexural properties (Sombatsompop et al. 2010) and conversely showed fatigue failure for the flat-wise direction (Pulngern et al. 2010). Lateral impacts in both wind and seismic situations were used for the conceptual study of WPVC log-wall behaviour. The presence of metal fasteners for WPVC log-wall installation directly affected lateral loads, especially under cyclic loading, whereas the in-plane lateral load of full-scale WPVC log walls with through-bolts showed higher hysteretic parameters in terms of strength and energy dissipation, as well as better structural stability than log walls without through-bolts (Eakintumas et al. 2022a,b).
WPVC composite houses are used as modern accommodations for convenience and comfortable living. Kanking et al. (2021) found that WPVC materials show high potential use for better housing (in terms of an insulator and energy consumption) compared with fibre-cement material. However, WPVC composite material is a wood-incorporated material, which needs to consider the influence of UV and condensation ageing, as well as the fungi and algae attacks that occur in seawater environments. Pattamasattayasonthi et al. (2011) found that the tensile and flexural properties of WPVC composites decreases with increasing ageing period, especially condensation. The yellowness and hydrophilicity of WPVC composite increases with the UV ageing period. The colour fading of the wood polymer composite surface is affected by chromophoric groups in the lignin, which enhance the UV adsorption of the wood polymer composite. High lignin content increases the crack development and discolouration in wood polymer composite as a function of the UV-weathering ageing period (Chaochanchaikul et al. 2012, 2013). The presence of wood particles in WPVC composites enhances the absorption of UV radiation.
Considering the wood types, anti-microbial agents and micro-organisms in WPVC materials, the addition of a UV-weathering ageing period diminishes the flexural properties and dimensional stability of WPVC/parawood materials, but the properties of neat PVC are not affected. UV-aged WPVC/Parawood decreases the anti-fungal performance for 32 days using Aspergillus niger (A. niger). The deterioration of the mechanical properties for WPVC/Parawood materials during ageing is diminished slightly by the addition of IPBC fungicide. However, the addition of fungicide slowly deteriorates WPVC/Parawood materials. IPBC is recommended in WPVC at a dosage of 10,000 ppm (Kositchaiyong et al. 2014a, b). Propylene glycol-based HPQM as a biocide, combined with hardwood for WPVC materials during UV ageing, has a similar result (Srimalanon et al. 2016). The addition of ZnB as a fungicide inhibits fungal growth in wood polymer composites but does not affect the physical-mechanical properties of the neat polymer or wood polymer composites (Chan-Hom et al. 2017). Moreover, the mechanical properties of PVC and WPVC materials are affected by the addition of wood and wood types, but not affected by using terbutryn as an algaecide. The anti-algal performance using Chlorella vulgaris (C. vulgaris) is suggested by terbutryn with a recommended dosage of 1,000 ppm in WPVC composites (Kositchaiyong et al. 2013).
In this work, the proportional contents of teakwood and parawood were varied in wood/poly(vinyl chloride) composite (WPVC) materials, which were subjected to UV-weathering ageing periods of 0, 4, 8, 16, and 32 days and seawater immersion periods of 0, 7, 30, 60, and 90 days. The fungicide and algaecide in WPVC composite materials were fixed at 10,000 (Kositchaiyong et al. 2014b) and 1,000 ppm (Kositchaiyong et al. 2013), respectively. Aspergillus niger TISTR 3012 and Chlorella vulgaris TISTR 8580 were used as marine fungi and marine algae. The mechanical properties (tensile and flexural properties) as well as anti-fungal and anti-algal activities were investigated. This work makes it possible to recommend a suitable ratio of teakwood and parawood for WPVC composite materials for applying the appropriate UV-weathering ageing and seawater immersion period.
EXPERIMENTAL
Materials Formulation and Specimen Preparation
PVC and its additives, wood particles, and anti-microbial agents were employed as shown in Table 1 (Kositchaiyong et al. 2013, 2014b). WPVC composite materials were prepared from PVC compounds and wood particles at a weight ratio of 50:50. The ingredients were mixed using a hi-speed mixer and blended by a twin-screw extruder with counter-rotating screws (HAAKETM model Rheomex CTW100 QC, Thermo Electron (Karlsruhe) GmbH, Germany) using a processing temperature between 140 to 160 °C and a screw speed not over 40 rpm. A compression moulding machine (Labtech Engineering Co., Ltd., Bangkok, Thailand) using a holding pressure of 150 kgf/m2 and heating temperature of 165 °C with pre-heating/heating/cooling step of 5/7/3 min was applied for moulding the PVC and WPVC specimens. The specimens are shown in Table 2.
Table 1. The Ingredients of Neat PVC and WPVC Composites
Table 2. The Formulations of Neat PVC and WPVC Composites
Wood Flour Characterisation
Wood flour characterisations consisted of a lignocellulosic constituent, specific surface area, particle size distribution, BET analysis, bulk density, SEM analysis, and aspect ratio, as shown in Table 3.
Table 3. The Characteristics of Wood Particles
Seawater Characterisation
As the testing medium for the seawater immersion conditions of WPVCs, this work used seawater obtained from a scuba diving zone around Koh Talu Island (Rayong, Thailand). The seawater was analysed using an ion chromatography analyser (Metrohm model 761 Compact IC, Switzerland) for characterisation of the ion composition of seawater before the test, as given in Table 4.
Table 4. The Ionic Compositions of Actual Seawater
Dimensional Stability
The cross-sectional areas of all specimens were measured after UV-weathering ageing and seawater immersion with any conditions before tensile and flexural tests, as the dimensional stability (Fig. 1). UV-weathering ageing and seawater immersion caused diffusion or penetration, which resulted in changes of cross-sectional areas in the specimens. Figure 1 shows the cross-sectional area of the specimens for tensile and flexural tests as a function of UV-weathering ageing and seawater immersion periods. Neat PVC had a smaller cross-sectional area than PVC with anti-microbial agents and WPVC composite materials. Particularly, WPVC composite materials had a larger cross-sectional area by approximately 5% for tensile (Fig. 1(a) and Fig. 1(c)) and 8% for flexural (Fig. 1(b), (d)) before UV-weathering ageing and seawater immersion, as compared with PVC with and without anti-microbial agents. PVC with anti-microbial agents showed a minor change with the addition of ageing periods. WPVC composite materials showed a larger cross-section by approximately 9% for tensile and flexural (Fig. 1(a) and Fig. 1(b)) during UV-weathering ageing periods, and approximately 14% for tensile and flexural (Fig. 1(c) and Fig. 1(d)) during seawater immersion periods because of water diffusion after ageing, compared with PVC with and without anti-microbial agents. Therefore, cross-sectional areas of all specimens have to be measured before testing the mechanical properties.
Seawater Micro-Organisms for Testing
Figure 2 shows the subculture procedures for seawater micro-organisms and cell counting before anti-microbial tests. Aspergillus niger TISTR 3012 and Chlorella vulgaris TISTR 8580 were representatively selected as a marine fungus and a marine alga, respectively, which were obtained from the Biodiversity Research Centre (BRC) and the Algal Excellent Centre (ALEC), Thailand Institute of Scientific and Technological Research (Pathum Thani, Thailand), respectively. A fungus was subcultured on Petri dishes of potato dextrose agar (PDA) using an incubator (Sanyo model MIR-153, United Kingdom) at a temperature of 30 °C for 7 days. The subcultured fungi having a diameter of 3 mm from a cork borer were continued in the flasks of potato dextrose broth (PDB) using a shaking incubator (JISICO model J-SIL, Korea) at 100 rpm with the same conditions before quantitative examination of fungal activity (Fig. 2(a)). Alga was subcultured on Petri dishes of BG-11 agar under a cool-white fluorescent lamp with an intensity of 2,000-3,000 lux at a temperature of 28 °C and a bright/dark cyclic period of 12/12 h for 14 days. One full scoop of an inoculation loop of the subcultured algae colonies was continued in the flasks of BG-11 broth under feeding O2 with the same conditions before the quantitative examination of algal activity, as shown in Fig. 2(b). The subculture of two microbes was controlled by using an aseptic technique.
Ageing Conditions
UV-weathering ageing
The specimens were tested under both UV and condensation ageing following ASTM G154-16 cycle 1 with testing periods of 0, 4, 8, 16 and 32 days, as shown in Chinkamonthong et al. (2013).
Seawater immersion
The specimens were immersed in an acrylic chamber with 250 mL of actual seawater for testing periods of 0, 7, 30, 60 and 90 days following ASTM C1202-19. The actual seawater was filtrated by membrane filters with an approximate diameter of 0.45 μm and sterilised by an auto-steam steriliser (Vision Scientific model VS-1321-60, Korea) at 121 °C with a pressure of 15 Ib/in2 for 15 min to eliminate the visible and invisible species, respectively. An acrylic chamber of actual seawater was shaken by a shaker (PNP Green SSeriker, Thailand) at 50 rpm during the test. The actual seawater in the acrylic chamber was changed for half of the testing periods, representing the seawater resistance behavior in the actual coastal applications.
Fig. 1. The cross-sectional area of the specimens for (a), (c) tensile and (b), (d) flexural tests as a function of UV-weathering ageing and seawater immersion periods
Fig. 2. The subculture procedures for seawater micro-organisms (a) fungi (b) algae and (c) cell counting, before anti-microbial tests
Mechanical Properties of PVC and WPVC Specimens
The tensile and flexural properties of the specimens after UV-weathering ageing and seawater immersion with any conditions were tested by following ASTM D638-14 with a testing speed of 5 mm/min and ASTM D790-17 with a testing speed of 1.36 mm/min using a universal testing machine (Shimadzu model Autograph AG-I, Tokyo, Japan).
Percentage Reduction of Fungal and Algal Growth
Quantitative examinations of A. niger and C. vulgaris activities for all specimens were modified slightly from ASTM D1413-07ε1 and ASTM D3731-20, respectively. The dried weight in mg/L for fungal growth and the chlorophyll-a content in μg/mL for algal growth were converted to the percentage reduction of species growths for all specimens.
Investigation of percentage reduction for fungal growth was initiated by preparing the subcultured A. niger cell suspension with an initial cell number of 1 x 104 cells/mL in flasks of PDB of 100 mL, whereas the subcultured C. vulgaris cell suspension with an initial cell number of 1 x 104 cells/mL in flasks of BG-11 broth of 100 mL was prepared for determining the percentage reduction of algal growth. An initial cell number of fungi and algae was counted by a haemocytometer (Precicolor HBG, Germany) and optical microscope (Meiji Techno Co., Ltd., Japan), and was also calculated by a dilution equation, as shown in Fig. 2(c). Square specimens (50 mm x 50 mm x 3 mm) were placed into 250 mL Erlenmeyer flasks containing PDB of 100 mL for the fungal test and placed into 250 mL Erlenmeyer flasks containing BG-11 broth of 100 mL for the algal test. Specimens for the fungal test were incubated and shaken by following Section of seawater micro-organisms for testing for 14 days, whereas the algal test was shaken by following Section of seawater micro-organisms for testing using a shaker (JEIO TECH model Lab companion SK-300, Korea) at a shaking speed of 150 rpm for 17 days.
The suctioning process of media for the specimens was applied after fungal incubation was done. The dried weight of fungi media in mg/L after using a hot-air oven of 80 °C for 3 days was calculated as the percentage reduction of fungal growth using the following Eq. 1, whereas the algal media of 1 mL of the specimens after algal incubation was done by being diluted with methanol 99.9% of 9 mL. The diluted algal media were placed in a dark room for 2 h to extract the chlorophyll-a. After the extraction process, the diluted algal media were centrifuged by a refrigerated centrifuge machine (Hettich Zentrifugen model Universal 32 R, Germany) at 5,000 rpm with a temperature of 4 °C for 5 min. The upper centrifuged algal media of 3 mL was examined by a UV/Visible scanning spectrophotometer (Mettler Toledo model UV5, Switzerland) to analyse the UV absorbance at wavelength numbers of 650 nm and 665 nm, as converted to the chlorophyll-a content. The chlorophyll-a content in μg/mL was also calculated as the percentage reduction of algal growth using Eq. 1,
Percentage reduction of fungal growth and algal growth (%) = [(C-S)/C] x 100 (1)
where C and S are dried weight in mg/L for fungal growth and chlorophyll-a content in μg/mL for algal growth of control and all specimens, respectively.
RESULTS AND DISCUSSION
Mechanical Properties
UV-weathering ageing condition
Figure 3 shows the tensile properties of the specimens as a function of UV-weathering ageing periods. Figure 3(a) shows the tensile modulus of the specimens as a function of UV-weathering ageing periods. The addition of anti-microbial agents both IPBC and Terbutryn slightly increased the tensile modulus of PVC compared with neat PVC. It did not clearly show any changes in the tensile modulus because there were small amount of the anti-microbial agents being added. The presence of wood particles increased the tensile modulus of the WPVC composite materials when compared with PVC with and without anti-microbial agents. This was due to the rigidity of wood particles. Considering teakwood and parawood with any ratios in WPVC composite materials, the presence of higher parawood content in WPVC composite materials (in formulations of 0:100, 20:80 and 40:60) showed the higher tensile modulus compared with the presence of higher teakwood content in WPVC composite materials (in formulations of 60:40, 80:20 and 100:0). This was because the higher tensile modulus of the WPVC composite materials was dominated by parawood content with greater particle size distribution, higher bulk density and lower porosity, both pore volume and pore size while the lower tensile modulus of the WPVC composite materials was dominated by teakwood content with lower particle size distribution, lower bulk density and higher porosity, both pore volume and pore size (as given in Table 3) (Frigione and Marra 1976; Amin et al. 2019; Pereira et al. 2020; Zhang et al. 2020; Weaver et al. 2021; Amin et al. 2022). Moreover, parawood has greater particle size distribution, higher bulk density and lower porosity in both pore volume and pore size, which showed higher density in WPVC than the effect of air bubbles in WPVC, as resulted in WPVC composite material with higher parawood content gave higher tensile modulus than with higher teakwood content. The addition of UV-weathering ageing periods decreased the tensile modulus of the specimens, which clearly showed in WPVC composite materials because of the degradation of wood particles in WPVC composite materials. However, WPVC composite materials with higher parawood content (in formulations of 0:100, 20:80 and 40:60) still indicated higher tensile modulus than those with higher teakwood content (in formulations of 60:40, 80:20 and 100:0).
Figure 3(b) shows the tensile strength of the specimens as a function of UV-weathering ageing periods. The addition of anti-microbial agents both IPBC and Terbutryn slightly increased the tensile strength of PVC when compared with neat PVC. The tensile strength of PVC with and without anti-microbial agents was similar to the tensile modulus, but decreased in WPVC composite materials. This was because wood particles in WPVC composite materials acted as defects due to incompatibility between wood particles and PVC matrix, though a silane coupling agent was applied. Wood particles also produce air bubbles in WPVC composite materials. In addition, wood particles of both teakwood and parawood did not contribute to the reinforcement in the WPVC composite materials.
Figure 3(c) shows the elongation at break of the specimens as a function of UV-weathering ageing periods. The presence of anti-microbial agents, both IPBC and Terbutryn, did not significantly affect the elongation at break of PVC compared with neat PVC. The presence of wood particles in both teakwood and parawood decreased the elongation at break of WPVC composite materials compared to PVC with and without anti-microbial agents, which conformed to the discussion of tensile strength, while the addition of UV-weathering ageing periods had no effect on the elongation break of WPVC composite materials.
Figure 4 shows the flexural properties of the specimens as a function of UV-weathering ageing periods. The flexural properties of both flexural modulus (Fig. 4(a)) and flexural strength (Fig. 4(b)) were consistent with the discussion of tensile properties.
Considering the effect of UV-weathering ageing periods on the properties of the WPVC composite materials, the tensile and flexural properties of both tensile modulus and tensile strength, and flexural modulus and flexural strength of the WPVC composite materials decreased when increasing the UV-weathering ageing periods. However, decreases in the properties of WPVC composite materials by the addition of UV-weathering ageing periods were mainly affected by the degradation of wood particles in WPVC composite materials.
Moreover, the presence of higher parawood content in WPVC composite materials (in formulations of 0:100, 20:80 and 40:60) showed higher sensitivity with UV-weathering ageing than the presence of higher teakwood content (in formulations of 60:40, 80:20 and 100:0). This was due to WPVC composite materials being composed of higher parawood content, as mixtures with lower total lignin (as given in Table 3) were more easily damaged from UV degradation onto wood particle in WPVC composite materials than of higher teakwood content as higher total lignin (as given in Table 3). This was supported by Sadeghifar and Ragauskas (2020) and Tran et al. (2021). It can be said that the addition of lignin content in WPVC composite materials contributed to the higher UV protection of materials (Espinoza-Acosta et al. 2022).
Fig. 3. (a) Tensile modulus, (b) strength, and (c) elongation at break as a function of UV-weathering ageing periods