Dimensional Instability Research Articles

Effects of superabsorbent polymer and natural zeolite on shrinkage, mechanical properties, and porosity in ultra-high performance concretes

The low water-to-binder ratio of ultra-high performance concrete (UHPC) often causes shrinkage and cracking due to early-age self-desiccation. This leads to significant initial dimensional instability, which may compromise structural integrity. As a promising solution, internal curing agents such as superabsorbent polymers (SAP) and natural zeolite have the potential to mitigate shrinkage and achieve self-stressing properties. This research aims to provide a comprehensive comparison between SAP and zeolite's effects within a consistent UHPC formulation. Six UHPC mixtures (including the reference mixture) were designed: three with SAP dosages of 0.2%, 0.4%, and 0.6% by cement mass, and two with zeolite replacing silica fume at 25% and 50% by mass. Various testing methods, including autogenous and drying shrinkage assessment, heat of hydration and thermogravimetric analysis, compressive strength evaluation, mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), were employed to assess the mixtures at different stages of curing. The result reveals that the incorporation of SAP and zeolite in the mixtures significantly reduces UHPC's early-age autogenous shrinkage. Moreover, SAP and zeolite additions impact mechanical properties, demonstrating that a balance between shrinkage control and compressive strength can be reached, through an optimization of the additions to achieve the desired performance. Microstructural analysis through MIP and NMR reveals increased overall porosity of the UHPC with SAP and zeolite, suggesting that low-field NMR can be a valuable tool for complementing conventional test methods. The outcome of this study provided valuable insights into optimizing the balance between durability and mechanical performance, paving the way for more sustainable and cost-effective applications of UHPC in modern construction practices.

Tile roof inspired structure optimization on radial wood to fabricate oil-water separation function

Cross wood was usually selected to fabricate oil-water separation function. However, the cross wood is easy to be deformed after chemical delignification. Therefore, structure optimization via drilling holes on radial wood along with nano Cu(OH)2/CuCl modification overcame the bottleneck defect of dimensional instability, and simultaneously fabricated oil-water separation function. The oil absorption capacity of modified wood increases with the number and depth of drilled holes, reaching a maximum of 3.7 g/g toward dichloromethane. The modified radial wood demonstrated exceptional filtration effectiveness toward dichloromethane/chloroform-water mixtures and exhibited superior photocatalytic degradation capabilities against methylene blue, malachite green, and direct blue 151 dyes. Additionally, the modified radial wood displayed favorable recycle ability for both oil-water separation and photocatalytic degradation. Thus, a facile, cost-effective and environmental friendly strategy proposed in this work has potential to enhance the practical application of wood based oil-water separation materials.

Dimensional and Structural Instability of Electrospun Polylactic Acid Membranes in Liquid Environments: Role of Water, Ethanol, and Temperature

Electrospun nanofibres of polylactic acid (PLA) are suggested for a variety of uses, including scaffolds for tissue engineering, components of drug delivery devices, sustainable packaging materials and membranes for liquid filtration/purification. For all these applications, it is critical to consider the stability of the PLA electrospun materials once in operation. Exposure to certain liquids and temperatures can modify their dimensions, shape, surface topography and mechanical response and compromise their performance. In this study, electrospun PLA mats were exposed to water and ethanol solutions, at different temperatures and for defined time periods, and changes in their properties were analysed. It was found that the impact of water on area shrinkage and fibre arrangement strongly depended on temperature, particularly if the treatment was performed at the glass transition temperature of PLA. Ethanol, instead, induced significant alterations in the size, morphology, and elastic modulus of the electrospun mats, even at room temperature and determined the formation of crimped structures. This work provides insights into the conditions that can critically affect the properties of PLA electrospun fibres and, hence, impact on their usage.

Characterisation of hygroelastic properties of compression and opposite wood found in branches of Norway spruce

The differential swelling seen between softwood opposite wood (OW) and its neighbouring compression wood (CW) developed in branches prompts several engineering issues such as dimensional instability and cracking. For a more efficient use of resources, the inevitable CW and OW should not be discarded or used as fuel, but incorporated into engineered wood products. Swelling is a hygroelastic phenomenon, where both the swelling and elastic properties of CW and OW are needed in order to make proper structural predictions. In this paper, swelling coefficients and moisture dependent elastic moduli for both CW and OW in the three principal material directions are provided along with measurements of moisture content, density, and microfibril angle. The small deformations necessitate the use of precise X-ray micro-computed tomography for measurements. The results indicate that CW and OW from Norway spruce branches differ in swelling, especially in longitudinal direction at low moisture content. It is noted that CW is a wood type with less pronounced anisotropic behaviour than both OW and normal wood from the stem, with the elastic moduli less sensitive to moisture changes in both longitudinal and transverse directions.

Distortion analysis in axial ultrasonic assisted milling of Al 7075-T6

Dimensional distortion and instability in the milling process of aluminum alloy parts can significantly increase production costs and result in defective parts. Therefore, distortion mitigation has long been a central focus of aerospace industry researchers. This article aims to investigate the effect of axial ultrasonic-assisted milling on distortion. In this study, the machining parameters effect in conventional milling (CM) and ultrasonic assisted milling (UAM) were experimentally and statistically investigated on distortion and milling force, and the results were subjected to a comparative analysis. Experiments provided compelling evidence of the technical advantages offered by axial ultrasonic-assisted milling, demonstrating its efficacy in reducing both milling force and distortion when compared to conventional milling. Furthermore, our study established a direct relationship between milling force and distortion. Applying the axial ultrasonic-assisted vibration resulted in a notable 29% reduction in cutting force compared to conventional milling. Additionally, UAM exhibited a reduction in distortion by approximately 21%. These findings have significant implications, particularly in improving the flatness tolerance of the workpiece, thereby yielding components free from waves and warpages.

Selected Physical and Mechanical Properties of Subfossil Oak (Quercus spp.) Compared to Aged Oak and Recent Oak

Subfossil oak (SO) wood material, originating from three different buried trunks discovered in recent years by excavations in riverbanks on Romanian territory, was analysed in this research. Aged oak recovered from constructions (AO_C) and recent/new oak wood material (NO) were also investigated to provide comparative data for the SO. The oven-dry density and the basic density, the total volumetric and linear swelling and shrinkage coefficients and the compression strength parallel to the grain were the selected physical and mechanical properties considered. The experimental results showed a lower density of SO compared to NO and AO_C tested by up to about 19–20%, alongside a trend of increased dimensional instability, with variability among the tested assortments. The compression strength parallel to the grain was reduced by 19–31% compared to NO. The properties of AO-C were closer to those of NO, but differences between wood materials from different sources and of different ages were registered. A positive linear correlation was found between compression strength parallel to grain and the basic density for all types of material and assortments tested. These comparative results have to be considered by designers and engineers in the valorisation of SO in furniture design and other applications.

Thermoswitchable catalysis to inhibit and promote plastic flow in vitrimers.

Acid-base catalysis is a common strategy to induce covalent bond exchanges in dynamic polymer networks. Strong acids or strong bases can promote rapid network rearrangements, and are simultaneously preferred catalysts for chemical reactions where maximum efficiency at the lowest possible temperature is aimed for. However, within the context of dynamic polymer networks, the incorporation of highly active catalysts can negatively affect the longer term application potential. Network dynamicity can diminish through catalyst ageing or quenching and highly active catalysts may prematurely activate bond exchanges, leading to dimensional instability and thus low creep resistance of the polymer networks. Herein, we present several examples where we explicitly explored weak acids (carboxylic acids) as catalysts for dynamic bond exchanges, using vinylogous urethanes (VU) as a well-understood protic acid catalysed vitrimer chemistry. Surprisingly, we have found that the sought-after long-term stability offered by a weak acid does not necessarily bring lower activity at high temperature. In fact, the weak acids show a remarkable thermoswitchable catalytic behaviour, going from an inactive hydrogen bonded state to an active state where the polymer matrix is protonated, with a profound impact on the network reactivity and rheology. Carboxylic acids with different electronic or steric environments show clear reactivity trends and their fine-tuning resulted in the most thermally responsive VU vitrimers studied to date. Our findings point out that catalyst choice and design for vitrimers is only poorly informed by catalyst performance in more traditional chemical reactions (in solvent), and that a more tailored catalyst design holds great promise for the field of vitrimers.

A New Method for Proportioning Sustainable, Economic, and Resilient Concrete

The ordinary Portland cement (OPC) component of concrete is the highest contributor to concrete’s cost and carbon footprint. Historically, code-writing organizations have required a high volume of paste in concrete mixtures by imposing minimum limits on the OPC content for a given application. However, high paste contents can result in dimensional instability, higher costs, higher carbon footprints, and lower durability. Minimizing the OPC content in concrete can provide economic, durability, and sustainability benefits. This study hypothesizes that the amount of OPC required to achieve some required fresh and hardened characteristics is highly dependent on the aggregate characteristics, supplementary cementing material (SCM) characteristics, and proportions of these. Given this, this research proposes using the amount of voids in the aggregate system (AV), or more specifically the paste volume-to-aggregate void ratio (PV/AV); SCM reactivity; and the SCM replacement level as key parameters to proportion concrete mixtures with minimum OPC contents to meet sustainability, economic, and resilience (SER) requirements. A new mixture proportioning procedure, referred to here as the SER proportioning method, is developed in this study based on assessing AV and identifying an optimal PV/AV that satisfies the required concrete characteristics. The results show that implementing the SER mixture proportioning method and including SCMs, or more specifically off-spec fly ashes (OFAs), can lead to significant reductions in the paste content and associated reductions in the cost and embodied carbon footprint of concrete.

Introduction of Eco-Friendly Finishing Method (YAKISUGI) among the Millennial Generation in Perina Village: Innovation in Unique Furniture Products with High Aesthetic Value

The demand for a diverse range of solid wood products has been steadily increasing. The unique grain patterns inherent to each wood species render solid wood products to possess distinct market segments. Nevertheless, the inherent vulnerabilities of wood as a biomaterial, such as susceptibility to decay, dimensional instability, and low resistance to organisms, necessitate specialized treatment for wood products. One environmentally sustainable treatment methodology, capable of enhancing the aesthetic value of wood, is the yakisugi finishing technique—a method involving the controlled charring of the wood surface. Notably, this technique remains relatively unfamiliar amongst small and medium-sized wood processing enterprises (UMKM) and the millennial generation. Consequently, this engagement initiative assumes significant importance in introducing the yakisugi finishing method to the millennial cohort. The unique visual characteristics of wood, engendered by this technique, hold the potential to serve as a catalyst for innovation in the realm of wooden product development by millennials. The engagement activities primarily encompass instructional modules, comprising theoretical elucidations and practical applications. Participants, affiliated with the youth group 'karang taruna,' have demonstrated appreciable enthusiasm towards the engagement activities that pertain to the yakisugi technique. It is anticipated that novel products will emerge as a result of the application of the yakisugi finishing technique, particularly within the domain of contemporary minimalist furniture products.

Study on the mechanism of excellent strength and toughness combination of a high nitrogen martensitic stainless steel treated by Q-C-P-T process

In this study, a high nitrogen martensitic stainless bearing steel with ultra-high strength and excellent toughness combination treated by quenching-cryogenic cooling-partitioning-tempering (Q-C-P-T) process was obtained. The yield strength, ultimate tensile strength, uniform elongation and the impact energy of the sample after partitioning at 200 °C for 1 h followed by tempering at 400 °C for 1 h are up to 2034 MPa, 2217 MPa, 5.83% and 58.73 J respectively. The microstructure characterization shows that the interstitial atoms of C and N in martensite diffuse into adjacent austenite during the partitioning process, resulting in the high stability of austenite. Strain-induced martensitic transformation was suppressed in maximum, effectively avoiding the formation of hard martensite enriched in C/N and dimensional instability caused by volume expansion of martensitic transformation, which is crucial for bearing steels. And nano-scale precipitates in the martensite matrix effectively compensate for the strength loss of the martensite caused by lower solid solution of carbon and nitrogen, thus obtaining excellent comprehensive mechanical properties. This work paves a new way for the development of advanced bearing steels.

Improvement of the Dimensional Stability of Rubber Wood Based on the Synergies of Sucrose and Tung Oil Impregnation

Rubber wood often exhibits dimensional instability during use, which seriously hinders its widespread application. In order to enhance the dimensional stability of rubber wood, a two-step method was employed in this study to modify rubber wood using two plant-derived compounds, namely sucrose and tung oil. Samples treated alone with sucrose or tung oil were also prepared. The water absorption, dimensional stability, and thermal stability of modified and untreated wood were evaluated. The results show that wood samples treated with 30% sucrose and tung oil had excellent water resistance and dimensional stability based on the synergistic effect of sucrose and tung oil. After 384 h of immersion, the 30% sucrose and tung oil group presented a reduction in water absorption by 76.7% compared to the control group, and the anti-swelling efficiency was 57.85%, which was 66.81% higher than that of the tung oil treatment alone. Additionally, the leaching rate of the 30% sucrose and tung oil group decreased by 81.27% compared to the sample modified with the 30% sucrose solution alone. Simultaneously, the 30% sucrose and tung oil group showed better thermal stability. Therefore, this study demonstrates that the synergistic treatment of modified rubber wood by sucrose and tung oil is an eco-friendly, economical, and highly efficient approach with the potential to expand the range of applications of rubber wood products.

Enhancing the properties of date palm fibre reinforced bio-epoxy composites with chitosan – Synthesis, mechanical properties, and dimensional stability

The present work deals with the mechanical behavior of dual bonding filler; chitosan (CTS) and date palm (DP) fibre in bio-epoxy composites. The primary objective of this research was to find out if the addition of CTS particles to a DP/bio-epoxy composite could enhance its mechanical properties. Bio-composites are being developed to better understand and manipulate the unique features of these versatile polysaccharides. CTS was included into the bio-epoxy matrix through solution mixing. Bio-epoxy composites with 40% DP fibre loading were developed by dispersing different CTS filler ratios - 5%, 10%, 15%, and 20%. For the purpose of comparison, a control sample was prepared without the inclusion of the CTS filler. The mixture was then manually disseminated for 7–10 min before being uniformly drenched into a steel cast mould with dimensions of 150 mm (width) 150 mm (length) 3 mm (thickness) and taken to the hot press, after which it underwent heating at a temperature of 110 °C for a duration of 10 minutes, while being subjected to a significant pressure of 250 bar. Tensile properties, impact properties, flexural properties, morphological characterization, water absorption, and thickness swelling were all measured on the prepared bio-composites. Among the CTS fractions, DP/CTS20 has the highest tensile strength (24.04 MPa) and tensile modulus (4.93 GPa), flexural strength (45.11 MPa), and impact strength (2.70 J/m2). The scanning electron microscope exposes the properties of fibres and polymers, as well as the reason for tensile test deficiency. Remarkably, bio-composites with higher CTS content have elevated moisture content and dimensional instability. Generally, we diagnosis that DP/CTS20 had the best tensile, flexural, and impact properties, as well as the highest water absorption and thickness swelling of any CTS compositions. The discovery improved our knowledge of bio-composite implementation trends, allowing us to assess their potential for more dependable implementations of much more sustainable green products. Furthermore, material enhancements such as bio-epoxy toughening to change the ductility behavior to improve energy absorption or natural fibre pretreatment can improve interbonding between the matrix and filler.

Li–Bi and Li–In alloys-based composite anode for lithium metal batteries

Lithium (Li) metal anode for high-energy-density secondary batteries has gained increasing attention in recent years due to its ultra-high specific capacity and the lowest redox potential. However, the Li anode suffers from severe issues including dimensional instability, Li dendrite growth, and low Coulombic efficiency (CE). In this work, a composite Li electrode (Li–Bi–In) with lithium–bismuth (Li–Bi) and lithium–indium alloys (Li–In) as the lithium host is fabricated to address the dimensional instability of the Li anodes. During Li stripping from the electrode, a porous structure composed of Li3Bi and Li13In3 alloys is formed and sustains the structural integrity. During Li plating, the Li3Bi alloy with high Young's modulus keeps stable, while the Li13In3 alloy with high lithiophilicity and ionic conductivity facilitates Li nucleation and uniform Li plating. Because of the synergistic effect of the two alloys, Li–Bi–In shows remarkable electrochemical performance. The symmetrical cell can stably cycle for more than 1200 h at a high current density of 5 mA cm−2. A full cell with Li–Bi–In anode and Li4Ti5O12 cathode stably runs for 200 cycles. This work provides a facile and effective strategy for fabricating lithium alloy-based composite anodes for lithium metal secondary batteries.

Evaluation of Physico-Mechanical Properties and Thermal Conduction to Energy-Saving Effects of Wood Compression Layered Structural Materials.

In this study, specimens were prepared from Japanese cedar (Cryptomeria japonica) with different thicknesses to determine the best hot-pressing conditions for wood compression layered structural materials (WCLS) through densification at various temperatures and compressing time conditions. However, residual stress-releasing after densification recovery can cause dimensional instability. To address this issue, the drying set method was combined with the compression-set recovery test to determine the best setting time. As a result, the bending strength and modulus of rupture (MOR) of WCLS increased by 9.98 ± 9.71 to 20.87 ± 13.09% and the modulus of elasticity (MOE) increased by 9.87 ± 11.92 to 22.40 ± 17.97%. The volumetric swelling coefficient (S), water absorption percent (WAP), and equivalent moisture content (EMC) decreased as the drying time increased. The anti-swelling efficiency (ASE) and moisture excluding efficiency (MEE) were found to be the highest at a drying time of 12 h, with values ranging from 13.20 ± 15.11 to 36.46 ± 6.83% and 15.18 ± 1.11 to 19.58 ± 8.31%, respectively. The drying method was found to be effective in increasing dimensional stability. The glass transition temperature (Tg) moved to a lower temperature as the compression-set increased, which was due to plasticization of wood caused by high temperature and pressure. The cell walls of WCLS presented viscous buckling, which provided effective dimensional stability. The thermal conductivity of Japanese cedar and each compression-set WCLS were 0.1863 ± 0.0071, 0.1520 ± 0.0147, 0.1817 ± 0.0106, and 0.1423 ± 0.0137 W/mK, respectively. The thermal conductivity of each WCLS increased with an increase in compression-set, but decreased by 10.67 to 22.52% compared to Japanese cedar. The total electricity energy consumption of each WCLS after 24 h of testing decreased with a trend of 30.50 ± 0.84, 29.83 ± 0.42, 29.57 ± 0.51, and 29.4 ± 0.36 kWH.

Investigating the Microscopic Mechanism of Ultrasonic-Vibration-Assisted-Pressing of WC-Co Powder by Simulation.

The ultrasonic-vibration-assisted pressing process can improve the fluidity and the uneven distribution of density and particle size of WC-Co powder. However, the microscopic mechanism of ultrasonic vibration on the powder remains unclear. In this paper, WC particles with diameter 5 μm and Co particles with diameter 1.2 μm were simulated by three-dimensional spherical models with the aid of the Python secondary development. At the same time, the forming process of the powder at the mesoscale is simulated by virtue of the finite element analysis software ABAQUS. In the simulation process, the vibration amplitude was set to 1, 2, and 3 μm. Their influence on the fluidity, the filling density, and the stress distribution of WC-Co powder when the ultrasonic vibration was applied to the conventional pressing process was investigated. The simulation results show that the ultrasonic vibration amplitude has a great influence on the density of the compact. With an increase in the ultrasonic amplitude, the compact density also increases gradually, and the residual stress in the billet decreases after the compaction. From the experimental results, the size distribution of the billet is more uniform, the elastic after-effect is reduced, the dimensional instability is improved, and the density curves obtained by experimentation and simulation are within a reasonable error range.

Shape distortion in composites: sources, characterization, and remedies

This paper reviews the shape distortions in a polymer composite, its sources, characterization techniques, and remedies. The shape distortion may include warpage, spring-in, or change in enclosed diameter for flat, angled, and circular parts. Residual stresses are considered to be the major source of shape distortion (dimensional instability) in laminated composites. These stresses are the result of the difference in thermal expansion behavior of the different plies or between matrix and reinforcement. Additionally, fiber buckling, transversal cracking, and delamination are also produced in the composite, affecting its mechanical properties like tensile, flexural, and compression. The produced residual stresses are determined through different techniques like layer removal of symmetrical laminates, first ply failure, and x-ray diffraction. The common remedies for shape distortion reported in the literature include nanoparticle addition and variable thickness at the base or flanges.

Robust, Fire-Retardant, and Water-Resistant Wood/Polyimide Composite Aerogels with a Hierarchical Pore Structure for Thermal Insulation.

The use of energy-saving materials is an effective strategy for decreasing energy consumption and carbon emission. Wood is a type of biomass material with a natural hierarchical structure, which results in its high thermal insulation. It has been widely used in construction. However, developing wood-based materials without flammability and dimensional instability is still a challenge. Herein, we developed a wood/polyimide composite aerogel with a well-preserved hierarchical pore structure and dense hydrogen bonds inside, resulting in its excellent chemical compatibility and strong interfacial interactions between its two components. This novel wood-based composite was fabricated by removing most hemicellulose and lignin from natural wood, followed by the fast impregnation using an 'in situ gel' process. The introduction of polyimide into delignified wood substantially improved its mechanical properties, with the compression resistance being improved by over five times. Notably, the thermal conductivity coefficient of the developed composite was approximately half that of natural wood. Furthermore, the composite exhibited excellent fire-retardancy, hydrophobicity, thermal insulation, and mechanical properties. This study provides a novel method for wood modification, which not only aids interfacial compatibility between wood and polyimide but also retains the properties of the two components. The developed composite can effectively reduce energy consumption, making it promising for practical and complex thermal insulation applications.

Effect of Neem Extract on Fungus Inhibition in Toona ciliata M. Roem.

The increasing human population and continuous demands of timber and its derived products like composite wood, has created a significant pressure on the demand for high quality timber from forests. This, ultimately has resulted in pressurising the natural forests and increase in the unvailibility of the production of high quality or durable timber from the forests. The one way to neutralize this pressure on the forests is to modify the other non durable wood species having undesirable properties like hygroscopicity, anisotropy, dimensional instability and biodegradability. Treatment with neem extracts as a biopreservative proves to be very efficient to protect the wood from bacterial or fungal rots. In the present study, wood specimens of Toona ciliata M. Roem. were treated with neem leaf and seed extracts for 72 hours in concentrations of 0.25, 0.5, 1, 1.5 and 2% (w/v), and analyzed for fungal growth and inhibition on dry weight basis using Polyporous rubidus. The fungal growth was maximum in untreated (control) samples whereas, minimum growth was observed in the neem leaf and seed extracts with 2.00% concentration. This method comes to be one of the most eco-friendly processes of wood preservation and helps in utilization of Toon wood in more effective and sustainable way. Also, the minimal release of harmful chemicals in the environment, helps to widen the industrial applications of Toona ciliata wood and make its acceptance to the society with ease.

Dimensionally stable, flame‐retardant, and leach‐resistant furfurylated wood prepared by incorporating ammonium polyphosphate and nano‐silica

AbstractFast‐growing plantation typically has some undesirable inherent qualities that restrict their use as engineering materials, such as dimensional instability, poor mechanical strength, and flammability (Sangregorio et al., Green Chem, 2020, 22, 2786–2798; Zhang et al., Fire Saf J, 2021, 121, 103297). In this study, a simple and environmentally friendly method was applied to improve low‐quality poplar wood by building an organic–inorganic hybrid system with a combination of biomass‐derived furfuryl alcohol (FA), ammonium polyphosphate (APP), and nano‐silica (nano‐SiO2). Different amounts of APP and nano‐SiO2 were mixed with a FA water solution, impregnated into the poplar wood followed by curing at 103°C to induce in situ polymerization of furfurylated wood (FW). The results showed that the FW/APP/SiO2 had strong self‐extinguishing properties, and passed the UL‐94 V‐0 rating with a limiting oxygen index (LOI) value as high as 49.5%. Results from cone calorimetry and thermogravimetry suggested that APP and nano‐SiO2 could have a synergistic effect, which successfully inhibited heat transfer and suppressed the smoke emission during its combustion by promoting char formation. Scanning electron microscopy shows that FA, APP, and nano‐SiO2 can basically penetrate into the cell wall and modify the wood fundamentally. FW/APP/SiO2 also enhanced the phosphorus fixation in the wood and greatly reduced its leaching into water, indicating it has long‐term fire resistance in service.

Impact of multiple recycling on the dimensional stability of wood–plastic composite made by the injection moulding process

ABSTRACT This study explored the effect of multiple recycling on the dimensional stability of wood–plastic composite. For this purpose, the injection moulding parameters effective on dimensional stability were first optimized based on the response surface method. Optical scanning, melt flow index (MFI), and differential scanning calorimetry (DSC) tests were used to analyse the shrinkage and deformation of recycled samples. The obtained results revealed that some recycled samples were subjected to thermal changes during the grinding and injection moulding process. The MFI and DSC results showed that the high-density polyethylene thermoplastic used in the wood–plastic composite was broken with long chains. Also, thermal changes occurred during the grinding and injection moulding process. The samples recycled three times had the highest dimensional instability (2.8% of shrinkage values). Finally, with the reduction of DSC, the semi-crystalline structure changed to amorphous, and the samples recycled four and five times had 2.7% and 2.5% shrinkage percentage, respectively.