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Ahmed, Sheikh Ali, Senior LecturerORCID iD iconorcid.org/0000-0002-6390-7377
Biography [eng]

My field of research interest is in liquid movement in wood, wood anatomy, wood modification, preservation and wood drying. I am also interested in non-destructive evaluation of wood and wood-based composites. I give emphasis on wood modification in an environmental benign way.

Biography [swe]

Mitt forskningsområde är impregnering av trä, träets anatomi, modifiering av trä, träskydd och torkning av trä. Jag är också intresserad av icke-destruktiv utvärdering av trä och träbaserade kompositer. Jag betonar vikten av trämodifiering på miljövänligt sätt.

Publications (10 of 30) Show all publications
Ahmed, S. A., Hosseinpourpia, R. & Adamopoulos, S. (2023). Micro-Fibrillated Cellulose in Lignin–Phenol–Formaldehyde Adhesives for Plywood Production. Forests, 14(11), Article ID 2249.
Open this publication in new window or tab >>Micro-Fibrillated Cellulose in Lignin–Phenol–Formaldehyde Adhesives for Plywood Production
2023 (English)In: Forests, ISSN 1999-4907, E-ISSN 1999-4907, Vol. 14, no 11, article id 2249Article in journal (Refereed) Published
Abstract [en]

Petrochemical-based phenol–formaldehyde (PF) adhesives are widely used in plywood production. To substitute phenol in the synthesis of PF adhesives, lignin can be added due to its structural similarity to phenol. Moreover, micro-fibrillated cellulose (MFC) can further enhance the bond performance, mechanical properties, and toughness of adhesive systems. Thus, the aim of this study was to evaluate the adhesion performance of lignin–PF (LPF) adhesives reinforced with MFC. In LPF formulations, three levels of MFC (0, 15, and 30 wt% based on the total solid content of adhesives) were added to the homogenous adhesive mixture. Three-layer plywood panels from birch (Betula pendula Roth.) veneers were assembled after hot pressing at 130 °C under two pressing durations, e.g., 60 and 75 s/mm. Tensile shear strength was measured at dry (20 °C and 65% RH) and wet conditions (water soaked at room temperature for 24 h). The results indicated that the addition of lignin reduced the strength of LPF adhesives in both dry and wet conditions compared to the control PF adhesive. However, MFC reinforcement enhanced the shear strength properties of the plywood. Furthermore, a longer pressing time of 75 s/mm slightly increased the shear strength.

Place, publisher, year, edition, pages
Switzerland: MDPI, 2023
Keywords
bio-based adhesives; tensile shear strength; viscosity; adhesive penetration; birch veneer
National Category
Composite Science and Engineering Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-125638 (URN)10.3390/f14112249 (DOI)001118094100001 ()2-s2.0-85178357748 (Scopus ID)
Available from: 2023-11-15 Created: 2023-11-15 Last updated: 2024-01-18Bibliographically approved
Ahmed, S. A., Hosseinpourpia, R., Brischke, C. & Adamopoulos, S. (2022). Anatomical, Physical, Chemical, and Biological Durability Properties of Two Rattan Species of Different Diameter Classes. Forests, 13(1), Article ID 132.
Open this publication in new window or tab >>Anatomical, Physical, Chemical, and Biological Durability Properties of Two Rattan Species of Different Diameter Classes
2022 (English)In: Forests, ISSN 1999-4907, E-ISSN 1999-4907, Vol. 13, no 1, article id 132Article in journal (Refereed) Published
Abstract [en]

Rattan cane is an important forest product with economic value. Its anatomical, physical, and biological properties vary with the cane height. This makes it difficult to select the appropriate cane diameter for harvesting. Understanding the material properties of rattan cane with different diameter sizes is important to enhance its utilization and performance for different end uses. Thus, the present study was performed on two rattan species, Calamus zollingeri and Calamus ornatus, at two different cane heights (bottom/mature and top/juvenile). Calamus zollingeri was studied at diameter classes of 20 mm and 30 mm, while Calamus ornatus was analyzed at a diameter class of 15 mm. The anatomical properties, basic density, volumetric swelling, dynamic moisture sorption, and biological durability of rattan samples were studied. The results showed that C. zollingeri with a 20 mm diameter exhibited the highest basic density, hydrophobicity, dimensional stability, and durability against mold and white-rot (Trametes versicolor) fungi. As confirmed by anatomical studies, this could be due to the higher vascular bundle frequency and longer thick-walled fibers that led to a denser structure than in the other categories. In addition, the lignin content might have a positive effect on the mass loss of different rattan canes caused by white-rot decay.

Place, publisher, year, edition, pages
Switzerland: MDPI, 2022
Keywords
Calamus zollingeri; Calamus ornatus; dynamic vapor sorption; basic density; volumetric swelling; white rot; mold
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-109313 (URN)10.3390/f13010132 (DOI)000757578800001 ()2-s2.0-85140985063 (Scopus ID)2022 (Local ID)2022 (Archive number)2022 (OAI)
Available from: 2022-01-17 Created: 2022-01-17 Last updated: 2023-05-02Bibliographically approved
Sivrikaya, H., Hosseinpourpia, R., Ahmed, S. A. & Adamopoulos, S. (2022). Vacuum-heat treatment of Scots pine (Pinus sylvestris L.) wood pretreated with propanetriol. Wood Material Science & Engineering, 17(5), 328-336
Open this publication in new window or tab >>Vacuum-heat treatment of Scots pine (Pinus sylvestris L.) wood pretreated with propanetriol
2022 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 17, no 5, p. 328-336Article in journal (Refereed) Published
Abstract [en]

Scots pine sapwood was pretreated with two levels of propanetriol (20% and 40% w/w glycerol), and then subjected to vacuum-heat treatment (VHT) at 180°C and 200°C. The treated samples were examined with respect to their weight and volumetric changes, mechanical properties, colour changes, and dynamic water vapour sorption. The weight of the samples after VHT did not change with increasing the temperature, but it was increased in glycerol pretreated samples. Combination of glycerol pretreatment and VHT decreased the maximum swelling. Total colour change was significantly higher during VHT at a higher temperature, while no obvious trend observed in the samples pretreated with glycerol. Modulus of elasticity (MOE) and modulus of rupture (MOR) were not affected by solely VHT, but strongly decreased after glycerol pretreatment. The equilibrium moisture content (EMC) of the samples decreased by VHT. The glycerol pretreatment caused a reduction in EMC values at a relative humidity (RH) below 60%, but considerably increased the moisture sorption in the RH above 75%. VHT slightly reduced the sorption hysteresis compared to untreated wood, but an apparent reduction in hysteresis observed by glycerol pretreatment. This indicates that the flexibility of the wood cell wall polymers increases due to glycerol pretreatment, which results in decreased MOE and sorption hysteresis values.

Place, publisher, year, edition, pages
Taylor & Francis Group, 2022
Keywords
Bulking, colour change, dynamic vapour sorption, glycerol, vacuum-heat treatment
National Category
Wood Science Polymer Technologies Polymer Chemistry
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-99741 (URN)10.1080/17480272.2020.1861085 (DOI)000599668600001 ()2-s2.0-85097819671 (Scopus ID)2020 (Local ID)2020 (Archive number)2020 (OAI)
Available from: 2020-12-30 Created: 2020-12-30 Last updated: 2023-02-16Bibliographically approved
Kovacikova, J., Kroon, M., Ahmed, S. A., Hosseinpourpia, R. & Adamopoulos, S. (2021). Mechanical properties of fiberboard composite bonded with polymer matrixcomputed by mean-field homogenization methods. In: Alberto Corigliano (Ed.), 25th International Congress of Theoretical and Applied Mechanics, August 22-27, 2021: Book of Abstracts. Paper presented at 25th International Congress of Theoretical and Applied Mechanics, August 22-27, 2021 (pp. 1984-1985). Milano, Italy
Open this publication in new window or tab >>Mechanical properties of fiberboard composite bonded with polymer matrixcomputed by mean-field homogenization methods
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2021 (English)In: 25th International Congress of Theoretical and Applied Mechanics, August 22-27, 2021: Book of Abstracts / [ed] Alberto Corigliano, Milano, Italy, 2021, p. 1984-1985Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

Nowadays, the design of composite materials considering sustainability and the environmental impact of the production is conspicuous. Therefore, in this work, we focus on investigating the mechanical behaviour and structure of a new green wood-based fibrous composite material bonded with a novel polymer matrix. The constitutive prediction models employing the material and structure design approaches simultaneously are proposed here to describe the material's microstructure. The goal is speeding up trials and reducing experiments expenses by replacing tests with computer simulations. Additionally, the relationship between material behaviour and structure is established and will be later used to generate Representative Volume Elements (RVEs) for finite element analysis (FEA).

Place, publisher, year, edition, pages
Milano, Italy: , 2021
National Category
Composite Science and Engineering
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-107713 (URN)9788365550316 (ISBN)
Conference
25th International Congress of Theoretical and Applied Mechanics, August 22-27, 2021
Available from: 2021-10-28 Created: 2021-10-28 Last updated: 2023-01-11Bibliographically approved
Jiang, W., Hosseinpourpia, R., Biziks, V., Ahmed, S. A., Militz, H. & Adamopoulos, S. (2021). Preparation of Polyurethane Adhesives from Crude and Purified Liquefied Wood Sawdust. Polymers, 13, Article ID 3267.
Open this publication in new window or tab >>Preparation of Polyurethane Adhesives from Crude and Purified Liquefied Wood Sawdust
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2021 (English)In: Polymers, E-ISSN 2073-4360, Vol. 13, article id 3267Article in journal (Refereed) Published
Abstract [en]

Polyurethane (PU) adhesives were prepared with bio-polyols obtained via acid-catalyzedpolyhydric alcohol liquefaction of wood sawdust and polymeric diphenylmethane diisocyanate(pMDI). Two polyols, i.e., crude and purified liquefied wood (CLW and PLW), were obtained fromthe liquefaction process with a high yield of 99.7%. PU adhesives, namely CLWPU and PLWPU,were then prepared by reaction of CLW or PLW with pMDI at various isocyanate to hydroxyl group(NCO:OH) molar ratios of 0.5:1, 1:1, 1.5:1, and 2:1. The chemical structure and thermal behavior of thebio-polyols and the cured PU adhesives were analyzed by Fourier transform infrared spectroscopy(FTIR) and thermogravimetric analysis (TGA). Performance of the adhesives was evaluated by singlelap joint shear tests according to EN 302-1:2003, and by adhesive penetration. The highest shearstrength was found at the NCO:OH molar ratio of 1.5:1 as 4.82 ± 1.01 N/mm2 and 4.80 ± 0.49 N/mm2 for CLWPU and PLWPU, respectively. The chemical structure and thermal properties of the cured CLWPU and PLWPU adhesives were considerably influenced by the NCO:OH molar ratio. 

Place, publisher, year, edition, pages
Basel, Switzerland: MDPI, 2021
Keywords
adhesive penetration; bio-polyol; bond strength; ethylene glycol; FTIR; liquefaction; pMDI; TGA
National Category
Polymer Chemistry
Research subject
Chemistry, Biotechnology
Identifiers
urn:nbn:se:lnu:diva-107151 (URN)10.3390/polym13193267 (DOI)000707987900001 ()34641084 (PubMedID)2-s2.0-85115799392 (Scopus ID)2021 (Local ID)2021 (Archive number)2021 (OAI)
Projects
Södra Stiftelse: Bio-based polyurethane adhesives for cross-laminated timber (CLT)Formas project 942-2016-2, 2017-21
Funder
Swedish Research Council Formas, 942-2016-2
Available from: 2021-09-27 Created: 2021-09-27 Last updated: 2024-01-17Bibliographically approved
Bobadilha, G. S., Stokes, C. E., Kirker, G., Ahmed, S. A., Ohno, K. & Lopes, D. J. (2020). Effect of exterior wood coatings on the durability of cross-laminated timber against mold and decay fungi. BioResources, 15(4), 8420-8433
Open this publication in new window or tab >>Effect of exterior wood coatings on the durability of cross-laminated timber against mold and decay fungi
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2020 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 15, no 4, p. 8420-8433Article in journal (Refereed) Published
Abstract [en]

Cross-laminated timber (CLT) is increasingly used in building construction worldwide. Durability of CLT against fungal attack has yet to be fully explored. Water intrusion in mass timber can yield dimensional changes and microbial growth. This study evaluated the performance of CLT coated with various water- and solvent-based stains commercially available in the United States. Twelve coatings were tested for moisture excluding effectiveness, water repellency effectiveness, volumetric swelling, and anti-swelling efficiency. Only five coatings repelled water, limiting dimensional changes. A modified version of AWPA E10-16 (2016) was performed to evaluate decay of the coated CLT samples. Weight losses were recorded after 18 weeks' exposure to the brown-rot decay fungus Gloeophyllum trabeum. In accelerated mold testing, coated CLT samples were grown in chambers containing spores of Aspergillus sp., Rhizopus sp., and Penicillium sp. for 29 d and assessed visually for mold growth. In both tests, coating C (transparent, water-based, alkyd/acrylic resin) performed the best among the tested coatings. Mold growth was completely prevented, and weight loss caused by G. trabeum was approximately 1.33%. Although coating C prevented decay for 18 weeks, coatings are not intended to protect against decay fungi. However, they may offer short-term protection during transport, storage, and construction. 

Place, publisher, year, edition, pages
USA: North Carolina State University, 2020
Keywords
Surface treatment, coatings, mass-timber, cross laminated timber deterioration, mold
National Category
Materials Engineering
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-98324 (URN)10.15376/biores.15.4.8420-8433 (DOI)000583802900078 ()2-s2.0-85096960224 (Scopus ID)
Available from: 2020-10-06 Created: 2020-10-06 Last updated: 2023-01-11Bibliographically approved
Sjökvist, T., Blom, Å. & Ahmed, S. A. (2020). Liquid water absorption in coated Norway spruce: Impact of heartwood, sapwood, density and weather exposure. MADERAS: Ciencia y Tecnología, 22(3), 335-346
Open this publication in new window or tab >>Liquid water absorption in coated Norway spruce: Impact of heartwood, sapwood, density and weather exposure
2020 (English)In: MADERAS: Ciencia y Tecnología, ISSN 0717-3644, E-ISSN 0718-221X, Vol. 22, no 3, p. 335-346Article in journal (Refereed) Published
Abstract [en]

Water is one of the most significant factors for the durability of wood. A common solution is to use a coating to protect and maintain low water content. However, little knowledge exists how the underlying wood substrate affects the water sorption of coated wood. Therefore, the liquid water absorption of coated and uncoated Norway spruce heartwood and sapwood with a variety of densities was measured by letting the panels float freely in the water. The effect of one year weathering of the coatings was also included. Coated heartwood and sapwood had no difference in water absorption in opposite to uncoated spruce. The influence of heartwood and sapwood seemed to have limited impact when a coating hindered the presence of free water. Wood density had a positive effect on the absorption of coated wood, i.e. low absorption for low-density samples, in opposite to uncoated samples. Low-density characteristic also contributed to a lower increase of water absorption after weather degradation, for samples with water-borne coatings. Natural weathering enhanced the effect of wood characteristics on coated samples, likely by an increase of coating permeability.

Place, publisher, year, edition, pages
Universidad del Bio-Bio, 2020
Keywords
Alkyd; acrylic; coating permeability; linseed oil; moisture content; Picea abies; wood durability
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-96953 (URN)10.4067/S0718-221X2020005000308 (DOI)000545887700008 ()2-s2.0-85091716511 (Scopus ID)
Available from: 2020-07-01 Created: 2020-07-01 Last updated: 2023-01-11Bibliographically approved
van Blokland, J., Adamopoulos, S. & Ahmed, S. A. (2020). Performance of thermally modified spruce timber in outdoor above-ground conditions: Checking, dynamic stiffness and static bending properties. Applied Sciences, 10(11), 1-25, Article ID 3975.
Open this publication in new window or tab >>Performance of thermally modified spruce timber in outdoor above-ground conditions: Checking, dynamic stiffness and static bending properties
2020 (English)In: Applied Sciences, E-ISSN 2076-3417, Vol. 10, no 11, p. 1-25, article id 3975Article in journal (Refereed) Published
Abstract [en]

Previous studies have shown that thermally modified wood (TMW) performs well in outdoor, above‐ground conditions in terms of resistance to wood‐decaying fungi. Yet, little is known about the development of defects such as checks and the corresponding mechanical properties of TMW in this condition. This experiment focused on the effect of 30 months outdoor above‐ground exposure (weathering) on the degree of checking, dynamic stiffness and static bending properties of thermally modified timber (TMT) of Norway spruce. Two board pairs per log were cut from 190 logs; one board of each pair was thermally modified and the other used as control. Then, 90 board pairs were exposed to the weather in south Sweden. Surface checking and axial stiffness were monitored at six‐month intervals by using digital photography and non‐destructive tests (time‐of‐flight and resonance method) to monitor changes in the material upon weathering. Finally, all boards were tested destructively in a 4‐point static bending test following EN 408 standard. Results showed that weathering had no significance influence on static bending properties of TMT even though the degree of checking was considerably higher in TMT than unmodified timber after weathering. In particular, checks along growth rings were deeper, longer and more common in TMT after weathering, especially on the pith side of boards. The maximum depth of these checks did not depend on board orientation (i.e., which side was exposed) and exceeded limits given in strength grading standards for 7% of the modified boards included. Axial dynamic stiffness determined at 6‐month intervals was less influenced by fluctuations in moisture content for TMT compared to unmodified timber, but did not confirm the increase in the degree of checking of TMT. The presence of checks from weathering did influence failure modes in TMT; horizontal shear failure became more frequent and some boards failed in compression.

Place, publisher, year, edition, pages
Basel, Switzerland: MDPI, 2020
Keywords
cracks, MOE, MOR, ThermoWood®, time‐of‐flight, resonance method, weathering
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-95788 (URN)10.3390/app10113975 (DOI)000543385900312 ()2-s2.0-85087013752 (Scopus ID)
Funder
Swedish Research Council Formas, 942‐2015‐722
Available from: 2020-06-08 Created: 2020-06-08 Last updated: 2023-01-11Bibliographically approved
Ahmed, S. A., Adamopoulos, S., Li, J. & Kovacikova, J. (2020). Prediction of mechanical performance of acetylated MDF at different humid conditions. Applied Sciences, 10(23), 1-16, Article ID 8712.
Open this publication in new window or tab >>Prediction of mechanical performance of acetylated MDF at different humid conditions
2020 (English)In: Applied Sciences, E-ISSN 2076-3417, Vol. 10, no 23, p. 1-16, article id 8712Article in journal (Refereed) Published
Abstract [en]

Change of relative humidity (RH) in surrounding environment can greatly affect the physical and mechanical properties of wood-based panels. Commercially produced acetylated medium density fiberboard (MDF), Medite Tricoya®, was used in this study to predict strength and stiffness under varying humid conditions by separating samples in parallel (//) and perpendicular (⊥) to the sanding directions. Thickness swelling, static moduli of elasticity (MOEstat) and rupture (MORstat), and internal bond (IB) strength were measured at three different humid conditions, i.e., dry (35% RH), standard (65% RH) and wet (85% RH). Internal bond (IB) strength was also measured after accelerated aging test. A resonance method was used to determine dynamic modulus of elasticity (MOEdyn) at the aforementioned humid conditions. Linear regression and finite element (FE) analyses were used to predict the MDF’s static bending behavior. Results showed that dimensional stability, MOEstat, MORstat and IB strength decreased significantly with an increase in RH. No reduction of IB strength was observed after 426 h of accelerated aging test. A multiple regression model was established using MOEdyn and RH values to predict MOEstat and MORstat. In both directions (// and ⊥), highly significant relationships were observed. The predicted and the measured values of MOEstat and MORstat were satisfactorily related to each other, which indicated that the developed model can be effectively used for evaluating the strength and stiffness of Medite Tricoya® MDF samples at any humid condition. Percent errors of two different simulation techniques (standard and extended FE method) showed highly efficient way of simulating the MDF structures with low fidelity.

Place, publisher, year, edition, pages
Switzerland: MDPI, 2020
Keywords
acetylation, wood fiber, strength, stiffness, internal bonding strength, thickness swelling, regression, finite element analysis
National Category
Paper, Pulp and Fiber Technology
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-99248 (URN)10.3390/app10238712 (DOI)000597741300001 ()2-s2.0-85097388989 (Scopus ID)
Available from: 2020-12-07 Created: 2020-12-07 Last updated: 2023-01-11Bibliographically approved
Ahmed, S. A., Adamopoulos, S., Poggi, F. & Walther, T. (2020). Resonance and time-of-flight methods for evaluating the modulus of elasticity of particleboards at different humid conditions. Wood research, 65(3), 365-380
Open this publication in new window or tab >>Resonance and time-of-flight methods for evaluating the modulus of elasticity of particleboards at different humid conditions
2020 (English)In: Wood research, ISSN 1336-4561, Vol. 65, no 3, p. 365-380Article in journal (Refereed) Published
Abstract [en]

Non-destructive testing of wood panels by either resonance or time-of-flight (TOF) methods provides possibilities for predicting their static bending properties. In the present study, three non-destructive devices (BING - Beam Identification by Non-destructive Grading by CIRAD, Montpellier, France, Fakopp Ultrasonic Timer and Sylvatest TRIO) were used for measuring the dynamic stiffness of different particleboard types. Fakopp Ultrasonic Timer and Sylvatest TRIO produce ultrasonic pulses to measure the sound velocity while BING uses resonance frequencies. Commercially produced particleboards with different thickness and densities were used to measure the dynamic modulus of elasticity (MOEdyn) in two directions (parallel and perpendicular to the production line) and at three different humidity levels (dry - 35%, standard - 65% and wet - 85% RH in constant temperature of 20°C ). MOEdyn of particleboards were correlated with the static moduli of elasticity (MOEstat) and rupture (MORstat). It was found that the non-destructive methods gave higher MOEdyn values in both production directions than that of MOEstat values. MOEdyn was found to decrease from dry to wet conditions. A very strong and statistically significant correlation existed between MOEdyn and static bending properties. MOEdyn correlated stronger to MOEstat than MORstat. At different humidity level, all three methods- Fakopp Ultrasonic Timer, BING and Sylvatest TRIO analyses showed good predicting capabilities to estimate MOEstat and MORstat of different particleboard types with high level of accuracy.

Place, publisher, year, edition, pages
Slovakia: Slovak Forest Products Research Institute, 2020
Keywords
Ultrasonic velocity, vibration methods, static bending, dynamic modulus of elasticity, wood panels
National Category
Paper, Pulp and Fiber Technology
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-96898 (URN)10.37763/wr.1336-4561/65.3.365380 (DOI)000545315000002 ()2-s2.0-85091222971 (Scopus ID)
Available from: 2020-06-29 Created: 2020-06-29 Last updated: 2023-01-11Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-6390-7377

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