Douglas Gardner - Profile on Academia.edu (original) (raw)

Papers by Douglas Gardner

Melt compounding of spray-dried cellulose nanofibrils/polypropylene and their application in 3D printing

Cellulose, Jul 10, 2024

BioResources, 2017

Cellulose nanofibrils (CNF) were investigated as a binder in the formulation of particleboard (PB... more Cellulose nanofibrils (CNF) were investigated as a binder in the formulation of particleboard (PB) panels. The panels were produced in four different groups of target densities with varying amounts of CNF binder. The produced panels were then tested to determine the modulus of rupture (MOR), modulus of elasticity (MOE), internal bond (IB), water absorption (WA), and thickness swelling (TS) properties. Density gradients through the thickness of the panels were evaluated using an Xray density profiler. The effect of drying on the strength development and adhesion between CNF and wood particles (WP) was investigated, and the effect of surface roughness on the wood-CNF bonding strength was evaluated through lap shear testing and scanning electron microscopy. It was found that at lower panel densities, the produced samples met the minimum standard values recommended for particleboard panels. Medium-density panels met the standard levels for IB, but they did not reach the recommended values for MOR and MOE. The possible bonding mechanism and panel formation process are discussed in light of microscopic observations and the results of lap shear tests were presented.

Journal of Coatings Technology and Research, 2017

Wettability and bonding quality of exterior coatings on fast-growing wood surfaces were studied. ... more Wettability and bonding quality of exterior coatings on fast-growing wood surfaces were studied. Samples of air-dried flat-grained (tangential surface) and edge-grained (radial surface) pattern of jabon (Anthocephalus cadamba) and sengon (Paraserianthes falcataria) woods were used. Before application of exterior coatings, the surfaces of the lumber samples were sanded. To provide wood surfaces with various degrees of roughness, abrasive papers of 120, 240, and 360 grits were used for the surface preparation. The wettability of two exterior coatings (water-based acrylic and oil-based alkyd varnishes) on the sanded wood surfaces was measured using a sessile drop contact angle method. The Shi and Gardner (S/G) model was used to evaluate and compare the wettability of the surface coatings on the wood. The sanded wood samples were coated with the two coatings (two layers each). Bonding quality of the coating layers was measured using a crosscut tape test method. Experimental results show that constant contact angle change rate (K value) of the S/G model decreased as the grit number of abrasive paper increased. This indicates that the wettability decreased as the roughness of the surface decreased (surface becomes smoother). There was no evidence of differences in wettability between tangential and radial wood surfaces. The oil-based alkyd coating generated better wettability compared to the water-based acrylic. The crosscut tests showed that the bonding quality of the coating films on both jabon and sengon wood decreased as the surface became smoother. The sengon wood compared to jabon wood provided better coating wettability and bonding quality. Wettability in terms of the K values was a good indication for determining the bonding quality of the two varnish layers.

Polymer, 2017

Fused layer modeling (FLM) or fused deposition modeling (FDM) can be used to produce polymer comp... more Fused layer modeling (FLM) or fused deposition modeling (FDM) can be used to produce polymer components with a cellular structure. The existence of cells (voids) in FLM parts degrades mechanical properties. This study was done to understand the influence of two printing parameters, layer height (0.1 mm and 0.3 mm) and extrusion temperature (200 ºC and 250 ºC), on the Izod impact strength of polypropylene (PP). Morphological analysis showed that smaller layer height and higher extrusion temperature generally resulted in smaller cell size but larger cell density. Printed PP components were lighter than injection molded PP parts. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses confirmed that both α and β type crystals existed in printed PP. PP printed at 250 °C had lower impact strength while components printed at 200 °C had similar impact strength to injection molded PP. Keyword. fused deposition modeling (FDM), polypropylene, impact strength.

Journal of Nanomaterials, 2016

Glycerine treated nanofibrillated cellulose (GNFC) was prepared by mixing aqueous nanofibrillated... more Glycerine treated nanofibrillated cellulose (GNFC) was prepared by mixing aqueous nanofibrillated cellulose (NFC) suspensions with glycerine. Styrene maleic anhydride (SMA) copolymer composites with different loadings of GNFC were prepared by melt compounding followed by injection molding. The incorporation of GNFC increased tensile and flexural modulus of elasticity of the composites. Thermogravimetric analysis showed that as GNFC loading increased, the thermal stability of the composites decreased marginally. The incorporation of GNFC into the SMA copolymer matrix resulted in higher elastic modulus (G′) and shear viscosities than the neat SMA copolymer, especially at low frequencies. The orientation of rigid GNFC particles in the composites induced a strong shear thinning behavior with an increase in GNFC loading. The decrease in the slope of elastic modulus with increasing GNFC loading suggested that the microstructural changes of the polymer matrix can be attributed to the incor...

Bioresources, Aug 9, 2016

An extensional flow mixture (EFM) system was studied, with the goal of achieving better distribut... more An extensional flow mixture (EFM) system was studied, with the goal of achieving better distributive and dispersive mixing. The effects of different mixing strategies (masterbatch method (MB), polyethylene-grafted maleic anhydride (PE-g-MA) as a compatibilizer, and compounding devices, such as a single screw extruder (SSE), a twin screw extruder (TSE), and an extensional flow mixer (EFM)) on the mechanical, thermal, rheological, and morphological properties of ultrafine cellulose (UFC)-filled highdensity polyethylene (HDPE) composites were investigated. Maximum tensile strength (17.7 MPa), tensile modulus (0.88 GPa), flexural strength (18.8 MPa), and flexural modulus (0.63 GPa) were obtained from the MB compounding method. The maximum stress-strain (13.8%) was obtained with EFM compounding. Polymer composites from SSE and SSE/EFM compounding methods with PE-g-MA exhibited slightly higher crystallinity compared with other compounding methods. The storage modulus of the samples prepared with the MB method was higher than those prepared with the SSE compounding method. The UFC-filled HDPE composites from the EFM compounding process exhibited lower melt viscosities than the other composites at high shear rates. Scanning electron microscopy (SEM) images showed the cellulose to be distributed and dispersed reasonably well in the HDPE matrix when using a coupling agent in combination with the MB and EFM compounding methods.

Theories and Mechanisms of Adhesion

Wood: Surface Properties and Adhesion

Wood surface properties and adhesion are dominated by its anatomical, chemical, and physical char... more Wood surface properties and adhesion are dominated by its anatomical, chemical, and physical characteristics. Wood can be categorized as a heterogeneous bio-polymer foam composite composed of cellulose, hemicellulose, lignin, and extractives. The differences among wood species as a function of anatomy, chemistry, or physical properties reinforce its description as having a heterogeneous nature. Because of the complex nature of wood structure and the myriad types of wood species, it is difficult to make sweeping generalizations about the surface properties of wood. It should be emphasized that although there are some surface property behaviors that are similar among different wood species, it is usually prudent to learn about the specific species of wood being adhesively bonded.

Optimizing lignocellulosic nanofibril dimensions and morphology by mechanical refining for enhanced adhesion

Carbohydrate Polymers, Dec 1, 2021

Using lignocellulosic nanofibrils as adhesive binders in structural composites is a growing field... more Using lignocellulosic nanofibrils as adhesive binders in structural composites is a growing field of interest attributable to their renewability, recyclability, and strength. A fundamental understanding of their adhesion mechanisms is crucial to tailor performance and optimize production costs. These mechanisms were elucidated by studying the morphology dependent adhesion in a model system composed of cellulose nanofibrils (CNFs) at different degrees of refinement and porous paper substrates. CNFs and lignin containing cellulose nanofibrils (LCNF) were characterized at different length scales using optical, atomic force, and scanning electron microscopy, revealing a complex distribution of sizes, spanning the macroscale to the nanoscale, which are modified unequally by refinement. Strong adhesion was correlated to a decrease in fiber size on the largest length scale and with an increase in relative fibril surface area. Flocculation hampered effective LCNF adhesion, but adding suspension stabilizers improved adhesion to levels comparable to CNF.

Gazi Üniversitesi Orman Fakültesi dergisi, Sep 15, 2018

Aim of study: In this study, it was aimed to establish and optimize a production process for engi... more Aim of study: In this study, it was aimed to establish and optimize a production process for engineering thermoplastic composites based on heat treated wood fillers and SMA copolymer. Material and Methods: As wood material, pine wood (Pinus strobus L.), and as a thermoplastic copolymer material, Styrene Maleic Anhydride (SMA) copolymer were used in this study. Heat treatment was conducted at 212°C for 8 h in an attempt to improve the durability of the wood furnish and the wood flour and SMA compounds were extruded and granulated using a lab-scale grinder. Physical test, mechanical test and morphological tests were calculated. Main results: The results showed that the highest tensile strength was in the 30 wt.% wood flour/SMA and it has been seen that the positive effect on FMOE,TMOE of heat treated wood flour/SMA. Weak interfacial bonding was observed between the polymer and wood filler from the SEM images of the fractured surfaces of wood flour/SMA composites. Research highlights: The results from this research indicated the compatibility of the SMA copolymer with the wood flour and the changes in the mechanical strength of the material. Due to limited heat treated wood thermoplastic composite usage in the field of wood engineering, there is a need for more extensive work in the future.

Toughened Renewable Bio-polyester Blends Achieved through Crystallization Retardation by Acetylated Cellulose Fibers

ACS Applied Polymer Materials

JOM, 2019

This research extends the existing classical lamination theory based finite element (FE) models t... more This research extends the existing classical lamination theory based finite element (FE) models to predict elasto-plastic and bimodular behavior of 3D printed composites with orthotropic material properties. Short carbon fiber reinforced acrylonitrile butadiene styrene was selected as the 3D printing material. Material characterization of a 3D printed unidirectional laminate was carried out using mechanical tests. A bimodular material model was implemented using explicit FE analysis to predict the tension and bending behavior of a 3D printed laminate. The results of the FE model predictions were experimentally validated. Hill's yield function was effective at predicting the elasto-plastic stress-strain behavior of the laminate in tension. In bending, bimodular material behavior along with Hill's yield function worked reasonably well in predicting the elasto-plastic bending of the laminate. The material model proposed can be used to predict the mechanical behavior of 3D printed parts with complex geometry under complex loading and boundary conditions.

Progress in Additive Manufacturing, 2018

Few commodity semi-crystalline thermoplastics in neat form are used in fused deposition modeling ... more Few commodity semi-crystalline thermoplastics in neat form are used in fused deposition modeling (FDM) because they experience dimensional instability (warping) during printing. In this study, a commercially available polypropylene (PP) filament for FDM processing was used to print tensile and flexural test samples. Three printing parameters were investigated: (1) extrusion temperature (200, 250 °C), (2) printing speed (45, 90 mm/s) and (3) layer height (0.1, 0.3 mm). Differential scanning calorimetry (DSC) showed that FDM printed PP samples had fewer α-crystals and more β-crystals than injectionmolded (IM) PP samples. Scanning electron microscopy (SEM) indicated that a higher extrusion temperature, slower printing speed and smaller layer height facilitated the molecular diffusion at the interfaces and created a smaller neck size within the printed parts. Density measurements showed that IM PP samples were denser than the FDM PP samples. No differences in density were found among the FDM PP samples. Compared to the IM PP, the mechanical properties decreased less for the PP printed at higher extrusion temperature (< 11.5%). The FDM PP parts had similar or even increased flexural modulus compared to the IM PP.

Industrial Crops and Products, 2016

Cellulose nanofibrils (CNFs) have shown their potential as the sustainable choice for reinforceme... more Cellulose nanofibrils (CNFs) have shown their potential as the sustainable choice for reinforcements in thermoplastic composites. Studies on surface properties are important because they directly relate to the compatibility between CNFs and polymer matrices. In this study, CNF suspensions were treated with two different organosilane functionalities before being spray-dried (SD). Three concentration levels of organosilane solution were applied based on the mass of the CNFs in suspension: 1 wt. %, 3 wt. % and 5 wt. %. Morphological and surface properties of the CNFs were measured to understand changes induced by the organosilane modification. Scanning electron microscopy analysis shows some aggregation of larger particles as well as many small twisted rectangular particles. Particle size distribution analysis (PSD) indicates certain differences among treated and untreated CNFs. Inverse gas chromatography (IGC) reveals that the organosilane treatment reduces the dispersion component of surface energy of dried CNFs and changed the acid-base characteristic of CNFs by the attachment of different functional end-groups.

IAWA Journal, 2015

Teak wood (Tectona grandis) as an important forest resource in Indonesia has been processed to wo... more Teak wood (Tectona grandis) as an important forest resource in Indonesia has been processed to wood furniture in large quantities to fulfill an increasing need of both local and international consumers. To satisfy the increasing demand for wood products, teak wood has been supplied from the State forests (Perhutani) and Community teak plantations. Community teak has been harvested at shorter age rotations (7–10 years) than Perhutani teak (40–60 years). This paper discusses the occurrence and characteristics of juvenile wood in Perhutani and Community teak based on density, shrinkage, bending strength (modulus of rupture - MOR, modulus of elasticity - MOE), fiber length, and microfibril angle (MFA). A segmented modeling approach was used to find the juvenile mature transition. Fiber length and MFA appear to be good anatomical indicators of radial increment demarcation between juvenile and mature wood, although maturation radial increment varies slightly between the fiber length and M...

Journal of Thermoplastic Composite Materials, 2019

The viscoelastic behavior of an extruded wood plastic composite (WPC) made from thermally modifie... more The viscoelastic behavior of an extruded wood plastic composite (WPC) made from thermally modified wood under hygrothermal treatment was studied and modeled. Multiple three-point bending creep/recovery tests were carried out using a dynamic mechanical thermal analyzer (DMTA) equipped with a submersible clamp. WPC specimens with a 15-mm span were subjected to two initial applied stresses; 9% and 14% of the flexural strength in 30 min of creep and 30 min of creep recovery under the combined effects of temperature (25°C, 35°C, and 45°C) and water immersion (saltwater (SW) and distilled water). A dry condition WPC control was used to compare the hygrothermal effects with respect to the control conditions. The WPC material in this article exhibited a linear viscoelastic behavior under the effect of temperature, whereas a nonlinear viscoelastic behavior was observed under immersion conditions. A power law model is considered a useful model to describe the creep behavior of WPC specimens w...

Bioresources, Apr 13, 2016

This study describes changes in the viscoelastic and thermal properties of composites made with v... more This study describes changes in the viscoelastic and thermal properties of composites made with various percentages (up to 20 wt.%) of a natural fiber blend (a mixture of flax, kenaf, and hemp fibers) and polyamide 6 (PA 6). According to the differential scanning calorimetry (DSC) analyses, the incorporation of natural fibers produced minor changes in the glass transition (Tg), melting (Tm), and crystallization temperature (Tc) of the PA 6 composites. Because of the reinforcing effect of natural fibers, the storage modulus (E') from dynamic mechanical thermal analysis (DMTA) increased as the natural fiber content increased. The E' values at room temperature and Tg were 3960 MPa and 1800 MPa, respectively, with the incorporation 20 wt.% fiber, which were 68% and 193% higher than the E' value of neat PA 6. As the natural fiber content increased, the thermal stability of the composites decreased, and thermogravimetric analysis (TGA) showed that the onset temperature of rapid thermal degradation decreased from around 440 (neat PA 6) to 420 °C (20 wt.% natural fiber blend). The addition of 20 wt.% single type fibers showed comparable DSC and TG results to the incorporation of 20 wt.% natural fiber blends.

Scientific Reports, Oct 10, 2019

Scientific Reports, Mar 6, 2019

Novel hybrid panel composites based on wood, fungal mycelium, and cellulose nanofibrils (CNF) wer... more Novel hybrid panel composites based on wood, fungal mycelium, and cellulose nanofibrils (CNF) were developed and investigated in the present study. In one set of experiments, mycelium was grown on softwood particles to produce mycelium-modified wood which was then hybridized with various levels of CNF as binder. The other set of experiments were conducted on unmodified wood particles mixed with CNF and pure mycelium tissue. It was found that the composites made of mycelium-modified wood and CNF resulted in enhanced physical and mechanical properties compared to the ones made by physically mixing wood, mycelium, and CNF. Scanning electron microscopy (SEM) images showed that mycelium modification covered wood particles with a network of fungal hyphae whereas CNF formed a uniform mycelial film over wood particles. Mycelium modification had a significant effect on reducing water absorption and thickness swelling of the hybrid composites and CNF increased the modulus of rupture and modulus of elasticity, optimally at 2.5% addition. We also present results and analysis pertaining to the development of unique lightweight composite systems with physical and mechanical properties optimized at 5% CNF addition with potential to be used in packaging and furniture applications. Lignocellulosic-based composites are receiving greater attention in recent years because they are renewable, biodegradable, and often eco-friendly compared with synthetic materials. However, the most commonly used adhesives used to bind those natural particles are formaldehyde-based resins 1 which limit the development of 100% natural-based composites. Moreover, formaldehyde emissions have been categorized as carcinogenic and toxic to humans 2,3. Limiting formaldehyde emissions from wood composite products is preferred in most applications 4-8. Recently, the US Environmental Protection Agency (EPA) finalized a rule to reduce exposure to formaldehyde emission from certain wood materials produced domestically or imported into the United States. These products include hardwood plywood, medium-density fiberboard, particleboard as well as household and other finished goods containing these products 9. The alternatives of formaldehyde-bonded composites are composites bonded by formaldehyde-free synthetic resins, natural-based resins and self-binding composites 10-15. Common natural-based resins that have been developed include carbohydrates, proteins, lignin, tannins, and synthetic molecules from natural sources rather than petroleum 16-21. Most recently, cellulose nanofibrils (CNF) have been demonstrated as a binder in conventional and novel composite systems. CNF has extremely high surface area and can bond wood particles and fibers through hydrogen bonding and mechanical interlocking, providing structural integrity to the composites 22-26. The technologies of producing self-binding composites include chemical or enzymatic pretreatments 27,28 , steam explosion 29 , steam injection pressing 30 and others. Enzymatic pretreatments basically treat wood or other agricultural fiber residues with phenol-oxidizing enzymes (laccase, peroxidases etc.) derived from white rot fungi or other sources 31. It is proposed that lignin is depolymerized during treatment and re-polymerizes during hot pressing. This technology has been used in different industries including textile, paper, wood, food and organic synthesis 10. Recently, mycelium-based biopolymer composites have been commercialized 32. Mycelia of filamentous fungi digest and bond to the surface of lignocellulosic materials, form entangled networks and provide mechanical strength to panels with fire resistance and acoustical absorption properties. So far, most of the studies have been