Functionalization of wood particles through a reactive extrusion process

Wood particles were modified in a reactive extrusion process with maleated polyethylene (MAPE) and maleated polypropylene (MAPP) compounds. Contents of MAPE were varied to study the effect of material composition on grafting efficiency during reactive extrusion, while extruder barrel temperatures and rotational screw speeds were varied to evaluate the effects of processing conditions on the modification of wood particles. Polymer molecular weight effects were followed using MAPP, with different molecular weights. Efficiency of the modification was assessed using FTIR and XPS surface analysis techniques, along with a titrimetric analysis, to verify the esterification reaction between the wood particles and maleated polyolefins. The grafting of maleated polyolefins onto the surface of the wood particles through a reaction of the hydroxyl groups on the wood surface with the maleated groups of the maleated polyolefins was confirmed, while the level of grafting of MAPE onto wood particles was determined to be a function of the MAPE concentration. However, there was no significant difference found in grafting efficiency at different extrusion processing conditions, rather all of the conditions resulted in adequate grafting. Similarly, there was no difference in grafting efficiency with the molecular weight of MAPP. Reactive extrusion was found to be a suitable technique for the modification of wood particles, with maleated polyolefins, for all of the material compositions and processing conditions studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3131–3142, 2006     

Thermoplastic modification of urea–formaldehyde wood adhesives to improve moisture resistance

Urea–formaldehyde (UF) resins are prone to hydrolytic degradation, which limits their use to indoor applications. This study examined the modification of UF resin with various thermoplastics as a means to increase the moisture resistance of the adhesive. UF adhesives were modified in situ with various hydrophobic and hydrophilic thermoplastic formulations, using either polar or nonpolar initiators. Unmodified and modified UF resins were characterized in terms of viscosity, pH, and gel time in their prepolymer suspension state. Cured solid UF resin plaques were prepared to isolate moisture sorption effects of the cured UF resin from that of the wood component in composites, which dominates their moisture uptake. Relative crosslink density and moisture sorption tests were run on cured UF resin plaques. Results indicated that viscosity increased after modification in most cases, with higher viscosities resulting from formulations using an acidic (polar) initiator. In all cases, activation energies of the curing reactions of thermoplastic‐modified UF suspensions were lower than the unmodified UF. High relative crosslink density compared to the unmodified UF was found for one sample, which correlated well with lower overall moisture sorption. Higher relative crosslink density of cured UF resin plaques appeared to be an indicator of lower moisture uptake. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4222–4229, 2006     

Bioprinting of Regenerative Photosynthetic Living Materials

Living materials, which are fabricated by encapsulating living biological cells within a non-living matrix, have gained increasing attention in recent years. Their fabrication in spatially defined patterns that are mechanically robust is essential for their optimal functional performance but is difficult to achieve. Here, a bioprinting technique employing environmentally friendly chemistry to encapsulate microalgae within an alginate hydrogel matrix is reported. The bioprinted photosynthetic structures adopt pre-designed geometries at millimeter-scale resolution. A bacterial cellulose substrate confers exceptional advantages to this living material, including strength, toughness, flexibility, robustness, and retention of physical integrity against extreme physical distortions. The bioprinted materials possess sufficient mechanical strength to be self-standing, and can be detached and reattached onto different surfaces. Bioprinted materials can survive stably for a period of at least 3 days without nutrients, and their life can be further extended by transferring them to a fresh source of nutrients within this timeframe. These bioprints are regenerative, that is, they can be reused and expanded to print additional living materials. The fabrication of the bioprinted living materials can be readily up-scaled (up to ≥70 cm × 20 cm), highlighting their potential product applications including artificial leaves, photosynthetic bio-garments, and adhesive labels.     

Performance effect on the TEG system for waste heat recovery in automobiles using ZnO and SiO2 nanofluid coolants

Enhancement in heat transfer of the cold side is vital to amplify the performance of a thermoelectric generator (TEG). With enriched thermophysical properties of nanofluids, significant improvement in heat transfer process can be obtained. The current study concerns the performance comparison of an automobile waste heat recovery system with EG‐water (EG‐W) mixture, ZnO, and SiO₂ nanofluid as coolants for the TEG system. The effects on performance parameters, that is, circuit voltage, conversion efficiency, and output power with exhaust inlet temperature, the total area of TEG, Reynolds number, and particle concentration of nanofluids for the TEG system have been investigated. A detailed performance analysis revealed an increase in voltage, power output, and conversion efficiency of the TEG system with SiO ₂ nanofluid, followed by ZnO and EG‐W coolants. The electric power and conversion efficiency for SiO ₂ nanofluid at an exhaust inlet temperature of 500K were enhanced by 11.80% and 11.39% respectively, in comparison with EG‐W coolants. Moreover, the model speculates that an optimal total area of TEGs exists for the maximum power output of the system. With SiO ₂ nanofluid as a coolant, the total area of TEGs can be diminished by up to 34% as compared with EG‐W, which brings significant convenience for the placement of TEGs and reduces the cost of the TEG system.     

A tool for meaning driven materials selection

There are several tools used in materials selection processes by designers. However, they are mostly engineering based tools, which are dominated by numerical (or technical) material data that is mostly of use in embodiment or detailed design phases of new product development. On the other hand, product designers consider certain aspects such as product personality, user-interaction, meanings, emotions in their material decisions. In this regard, existing tools and methods do not fully support designers in their materials selection processes. This paper describes the development of a new materials selection tool holding the idea of [meaning driven materials selection]. In addition, the paper consists of a study conducted to create data for a dummy application.     

Influence of processing conditions and material compositions on the performance of formaldehyde‐free wood‐based composites

This study examined the differences between formaldehyde‐free wood composite panels made with maleated polyethylene (MAPE) and maleated polypropylene (MAPP) binding agents. Specifically, the study investigated the contrasts of (a) base resin type, PE vs. PP, (b) molecular weight/maleic anhydride content in MAPP binding agents, and (c) the manufacturing methods (reactive extrusion vs. hot press) on the physicomechanical properties of the composites. FTIR and XPS analyses of unmodified and modified wood particles after reactive extrusion with maleated polyolefins provided evidence of chemical bonding between the hydroxyl groups of wood particles and maleated polyolefins. Although extruding the particles before panel pressing gave better internal bond (IB) strength, superior bending properties were obtained through compression molding alone. MAPP‐based panels outperformed MAPE‐based panels in stiffness. Conversely, MAPE increased the IB strength of the panels compared with MAPP. Polymer base resin had no effect on modulus of rupture or screw holding capacity. Differences between the two maleated polypropylene compounds were not significant for any of the mechanical properties tested. Formaldehyde‐free wood composites manufactured in this study often outperformed standard requirements for conventional particleboard, regardless of material composition or manufacturing method used. POLYM. COMPOS., 27:599–607, 2006. © 2006 Society of Plastics Engineers     

Thermohydraulic performance of a new internal twisted ribs automobile exhaust heat exchanger for waste heat recovery applications

The performance of the thermoelectric-based waste heat recovery (WHR) system in an automobile greatly depends on the amount of heat extracted by the exhaust heat exchanger (EHE). In the present study, the thermohydraulic performance of the EHE having twisted ribs and the pressure drop across the entire heat exchanger have been experimentally investigated. The experiments were repeated for the various geometric parameters such as twist ratio (4-8), angle of attack (30°-90°), and pitch ratio (6-10) on the Reynolds number within the range of 2300 to 25,000. The heat transport and fluid flow characteristics were compared with an internally smooth EHE using the thermohydraulic performance parameter. The maximum heat transfer rate was improved at 164.22%. However, the specification of the twisted rib for superior performance has been obtained at twist ratio of 4 and pitch ratio of 8 with 60° angle of attack. The highest thermohydraulic performance parameter value revealed as 1.93 at the same configuration. With the change in twist ratio, the pitch ratio, angle of attack, and the heat transfer rate increased by 39.52%, 60.85%, and 40.70%, respectively. Thus, the efficient heat transfer with the twisted rib would improve the extent of WHR in automobiles.     

Composite materials manufactured from wood particles modified through a reactive extrusion process

Wood‐based composites such as particleboard and medium‐density fiberboard are currently made with formaldehyde‐containing adhesives. Since the government is continuously developing and implementing very stringent regulations to eliminate formaldehyde emissions into the environment, alternative approaches must be developed to replace these adhesives. This study examined the concept of using a reactive extrusion process as a means of developing a new, formaldehyde‐free binding system for wood composite products. The surfaces of wood particles were modified by grafting maleated polyolefins through a continuous reactive extrusion process. Chemical changes resulting from this treatment were followed by studying the Fourier transform infrared (FTIR), ¹³C nuclear magnetic resonance (NMR), and X‐ray photoelectron spectroscopy (XPS) spectra. The modified wood particles were compression‐molded into panels, which were tested for mechanical properties. FTIR, ¹³C NMR, and XPS data revealed that the chemical reactions have taken place between the hydroxyl groups of wood particles and maleated polyolefins. The mechanical property test results indicated that the composite panels compared favorably with current standard requirements for conventional particleboard. POLYM. COMPOS., 26:534–541, 2005. © 2005 Society of Plastics Engineers     

Modeling and optimization of formaldehyde‐free wood composites using a Box‐Behnken design

A response surface model using a Box‐Behnken design was constructed to statistically model and optimize the material compositions‐processing conditions‐mechanical property relationships of formaldehyde‐free wood composite panels. Three levels of binding agent content, pressing time, and press temperature were studied and regression models were developed to describe and optimize the statistical effects of the formulation and processing conditions on the mechanical properties of the panels. Linear models best fit both the flexural strength (modulus of rupture [MOR]) and internal bond (IB) strength of the panels. Increasing any of the manufacturing variables resulted in greater MOR and IB strength. Flexural stiffness (modulus of elasticity [MOE]) was best described by a quadratic regression model. Increased MOE could be obtained through higher pressing times, binding agent concentrations, and/or pressing temperatures. However, binding agent concentration had less effect on increasing the MOE at higher pressing temperatures. Numerical optimization showed that formaldehyde‐free panels with desired mechanical properties could be manufactured at pressing temperatures ranging from 187.18 to199.97°C, pressing time from 3.31 to 8.83 minutes, and binding agent concentration from 7.66 to 11.86%. POLYM. COMPOS., 27:497–503, 2006. © 2006 Society of Plastics Engineers