Footwear Components Research Articles

Improving the mechanical and electrostatic properties of polymer composites for personal protective equipment by incorporating graphite into a poly(vinyl chloride) polymer matrix

The objective of the study was to examine the mechanical and electrostatic properties of poly(vinyl chloride) intended for use in protective footwear. The poly(vinyl chloride) material was made with graphite (flake side dimensions 5 and 10 µm) additive in weight concentration variants from 0.5 to 10.0%. The influence of incorporating graphite in the polymer matrix was evaluated by testing mechanical parameters and electrostatic parameters (according to Standard No. EN ISO 20344:2021). In addition, the surface morphology, analysis of thermal properties and stability were evaluated. The results indicated the highest increase in tear resistance for the variant containing 1.5– 2.0% graphite. In terms of electrostatic parameters, the addition of graphite caused an increase in electrical resistance. Based on the obtained preliminary test results, it can be concluded that the use of graphite additive can increase the mechanical properties and find application in the production of protective footwear components.

Additive Manufacturing of Smart Footwear Components for Healthcare Applications.

Diabetic foot complications pose significant health risks, necessitating innovative approaches in orthotic design. This study explores the potential of additive manufacturing in producing functional footwear components with lattice-based structures for diabetic foot orthoses. Five distinct lattice structures (gyroid, diamond, Schwarz P, Split P, and honeycomb) were designed and fabricated using stereolithography (SLA) with varying strand thicknesses and resin types. Mechanical testing revealed that the Schwarz P lattice exhibited superior compressive strength, particularly when fabricated with flexible resin. Porosity analysis demonstrated significant variations across structures, with the gyroid showing the most pronounced changes with increasing mesh thickness. Real-time pressure distribution mapping, achieved through integrated force-sensitive resistors and Arduino-based data acquisition, enabled the visualization of pressure hotspots across the insole. The correlation between lattice properties and pressure distribution was established, allowing for tailored designs that effectively alleviated high-pressure areas. This study demonstrates the feasibility of creating highly personalized orthotic solutions for diabetic patients using additive manufacturing, offering a promising approach to reducing the plantar pressure in foot and may contribute to improved outcomes in diabetic foot care.

A chemical modification-free strategy for fabricating tough and tear-resistant natural rubber/polysaccharide material

Natural rubber latex (NRL) is widely used in a variety of products, including gloves, balloons, condoms, and foamed items like pillows and footwear components. However, the limitations of traditional NRL materials in terms of tear resistance and toughness restrict their use in high-end applications. Hence, developing tough and tear-resistant NRL materials using eco-friendly and user-friendly methods remains highly desirable. In this work, a chemical modification-free method is reported for the fabrication of tough and tear-resistant vulcanized natural rubber/carrageenan material (SNR/KC). KC is introduced into NRL via a modified latex mixing strategy, which can form hydrogen bonds with the non-rubber components (NRC) such as proteins on the surface of natural rubber latex particles. As a result, KC can be well dispersed and form a segregated network structure within the rubber matrix. The rigid filler network created by KC effectively impedes crack propagation and enhances energy dissipation during deformation. Furthermore, the presence of KC in the NR matrix fosters the strain-induced crystallization (SIC) of NR. All these contribute to the superior tear resistance and toughness of composite materials. With only 0.1 phr of KC, the composite exhibits a fracture toughness of 208.4 kJ/m2 and a tear strength of 50 kN/m. This work demonstrated that the interaction between polysaccharide and NRC of NRL can be leveraged to fabricate tough and tear-resistant NR composites without any chemical modification and tedious process, favoring a green development and high-quality pursuit of NRL materials.

Allergens causing contact dermatitis of the feet: Investigation and analysis of allergic reaction causes.

Allergic contact dermatitis of the feet is a significant problem that affects the quality of life and requires attention from the medical community due to the number of studied and still unidentified allergens. The purpose of this review article is to summarize the available scientific data regarding the most common allergens that cause ACD of the feet. Nickel sulphate, neomycin sulphate, thiuram mix and colophony occupy a significant place in the prevalence of allergies. The prevalence of sensitization to rubber and leather products can vary depending on the ethno-demographic characteristics of the country, as well as the specifics of a person's professional activity, such as the use of protective waterproof shoes, increased humidity of the microclimate, and atopy in anamnesis. Patch testing has been shown to be an important method for identifying allergens, however, not all footwear components are tested during patch testing with standard allergen series, requiring the use of patches made from patient shoe samples. Expanding the scope of patch testing to include other possible allergens is important for the accurate diagnosis of ACD of the feet and a more detailed study of those allergens that were previously considered rare.

Mathematical model for footwear upper material consumption estimation

Appropriate material consumption estimation since the design phase for footwear fabrication is a vital issue as material costs account for a sizeable portion of the overall production cost of a pair of shoes. This paper presents a mathematical model to predict the calculation of footwear upper material consumption to improve the utilization ratio of materials through a suitable nesting map onto leather. The proposed model concentrates on the two-dimensional geometry of footwear components and the application of rich mathematical concepts. The model reflects the outlines of individual footwear components while determining the area using definite integral calculus. Five distinct rotational kinds are applied for component arrangements that correlate to the physiognomy of leather because nesting onto the leather is intractable. The simple concept of a minimal-area polygonal enclosure is applied to maximize material utilization with minimum waste. Finally, the model was verified for four consecutive Oxford footwear sizes by comparing actual upper material consumption with predicted upper material consumption. The noble contribution of this analysis is to use ImageJ software to compute upper material consumption in real case analysis through image processing techniques and separate estimation of wastes, especially the fourth waste. The results of the comparison study show that the proposed model can reduce average material requirements by 2.06 %. This minimization of waste could be beneficial in terms of economic and environmental sustainability. Therefore, this study can be applied to estimate more accurately the amount of upper material required for footwear fabrication and support better utilization of material in the footwear industry.

HAPTIC digital 3D printing on textile surfaces for high-volume footwear manufacturing

A new digital dispensing process was developed for applying waterborne textile HAPTIC coatings in a fully automatically controlled new 3D printing process. A continuous line width can be controlled by the quantity of ink flow, nozzle speed, and geometrical nozzle design.Inaccuracies in the printing pattern found at the start and end points of the dispensing process, were overcome by developing a smart-plunger-based dosing system. Excellent bonding to textiles based on synthetic fibers could be achieved, and all properties required for athletic footwear applications could be met, including flexing and abrasion performance. It could be demonstrated that the HAPTIC coating technology could be transferred from a large-scale industrial screen printing process into a fully automatic digital 3D dispensing process. The Design determines printing speed and resolution, but initial evaluation of overall costs indicates that dispensing process on flat and curved surfaces could be very well suitable for full upscaling into mass production of footwear components.

Effect of Processing Time of Steam-Explosion for the Extraction of Cellulose Fibers from Phoenix canariensis Palm Leaves as Potential Renewable Feedstock for Materials.

This paper briefly discusses the utilization of pruning wastes as a lignocellulosic source of cellulose fibers, which could be of potential use in the development of valuable materials such as sustainable textiles and fillers for footwear components including uppers and soles. Phoenix canariensis palm leaves, one of the most common plants found in the local environment of the Alicante region (Spain), was used as a biomass raw material. Determining appropriate processing parameters and their desired range of maximum cellulose extraction states is key to improving yields. Therefore, this study aimed at determining the effect of processing conditions on cellulose extraction by optimizing the hydrothermal process, as a part of overall combined processes involving several steps. Specifically, the time of the steam-explosion stage was varied between 15 and 33 min in order to maximize the cellulose extraction yield. The composition of both the extracted fibers and the resulting by-product solutions generated during the different steps were determined by FTIR and TGA in order to analyze the effectiveness of removing hemicellulose, lignin and extractives as well as the removed substances at each stage for their further valorization. Additionally, the morphology of cellulosic fibers was evaluated by SEM and their crystallinity by XRD. Crystalline cellulose fibers were successfully extracted from pruning biomass wastes, achieving more efficient removal of hemicellulose and lignin when the hydrothermal process was assessed over 25-33 min. This resulted in finer and smoother fibers, but the crystallinity of α-cellulose decreased as the time of steam-explosion increased to 33 min. The characterization of waste solutions generated after the different extraction steps confirmed that the most effective treatments to remove lignin and hemicellulose from the cell wall are alkaline pretreatment and a hydrothermal process.

Heavy metals in leathers, artificial leathers, and textiles in the context of quality and safety of use

The article presents research findings on the content of arsenic, cadmium, chromium, copper, lead, and zinc in extracts from leathers, artificial leathers intended for footwear components, and textiles. After extracting the metals using an artificial acidic sweat solution, their contents were quantitatively determined by atomic absorption spectrometry. In the cotton textiles, the metal contents were in accordance with the OEKO-TEX limits, while regarding the artificial leathers, only the acrylic knit fur had a too high chromium content (1.1 mg/kg) as compared with the requirements of the STANDARD 100 by OEKO-TEX for products intended for children (< 1.0 mg/kg). The chromium content in lining and upper leather (> 228.0 mg/kg) exceeds the limits for children’s products (< 2.0 mg/kg), but also the less restrictive ones for other products (< 200.0 mg/kg). Regarding the other metals, the leathers met the OEKO-TEX requirements. Approved materials may have elevated heavy metal contents, as demonstrated for chromium. The presence of heavy metals in too large amounts in products is a serious problem due to their allergenic and toxic effect. Therefore, action should be taken aimed at more effective detection and elimination of such products from markets and at reducing the use of chemicals containing harmful metals in manufacturing processes.

Parents, health professionals and footwear stakeholders’ beliefs on the importance of different features of young children’s footwear: a qualitative study

BackgroundA small but building pool of evidence of the impact of footwear on children’s function means understanding the different beliefs of stakeholders about footwear key features and flexibility is critical for translation into recommendations and to support parents and caregivers in purchasing footwear for their children. Therefore, this research aimed to describe how different stakeholders (health professionals, parents, and footwear industry representatives) described the importance of flexibility and other footwear features for young children.MethodsThis qualitative study was nested within an international modified Delphi online survey. Participants responded to open-ended questions about footwear component flexibility and asked if and why flexibility in these areas were important. Participants also described any other important footwear features. Inductive thematic analysis was used to generate themes.ResultsThere were 121 responses from three stakeholder groups including health professionals (n = 90), parents of young children (n = 26) and footwear industry representatives (n = 5). Overarching themes described by participants included developmental impacts of footwear, therapeutic impact and how footwear may play a role in function.ConclusionThere were key differences in how stakeholders viewed footwear and any perceived benefits of footwear components, much of which was not backed with empirical evidence. It was also identified that health professionals are using footwear within treatment recommendations. This work highlights the importance of understanding circumstances in which footwear may have a therapeutic impact or be the first line of treatment for children with complex foot needs. This is the first step in developing contemporary footwear recommendations for parents and caregivers.

EVA/starch/POE composite for footwear material: How the chemical composition affects its properties compared to standards

The usage of biodegradable foam material in footwear components has positive impacts on environmental sustainability when disposed into landfills. This study was aimed to investigate the effects of polyolefin elastomer (POE) on its properties of foamed EVA/cassava starch composites compared to standards. Foamed EVA/cassava starch composites were prepared by mixing EVA, cassava starch, and additives using a two-roll mill laboratory scale. Content of POE was varied 10-20 phr. The ratios of EVA/cassava starch were varied from 90/10; 80/20; 70/30; and 60/40. Effects of POE were characterized its density, tensile properties, tear strength, permanent set, abrasion resistance, flex resistance, morphology, and biodegradability. It was found that the increase of POE content in EVA/starch composites increased the density and abrassion resistance, but decreased the tensile strength, elongation at break, and permanent set properties. The best formula of foamed EVA/cassava starch/POE composites for footwear materials contains EVA 80 phr, starch 20 phr and POE 20 phr with density 0.983 g/cm³, tensile strength 22.27 kg/ cm², elongation at break 645.67%, tear strength 9.42 N/mm, volume loss 88.907 mm, no crack when flexed 150 kcs. These results met the requirements of SNI 0778:2009-Sol Karet Cetak for quality classifcation 3 of outsoles. The foamed composite containing POE20 has denser morphology than POE10, while the addition of POE has no signifcance in weight loss after burial test

Simultaneous Sonochemical Coloration and Antibacterial Functionalization of Leather with Selenium Nanoparticles (SeNPs).

The development of antibacterial coatings for footwear components is of great interest both from an industry and consumer point of view. In this work, the leather material was developed taking advantage of the intrinsic antibacterial activity and coloring ability of selenium nanoparticles (SeNPs). The SeNPs were synthesized and implemented into the leather surface by using ultrasonic techniques to obtain simultaneous coloring and functionalization. The formation of SeNPs in the solutions was evaluated using UV/Vis spectroscopy and the morphology of the NPs was determined by transmission electron microscopy (TEM). The treated leather material (leather/SeNPs) was characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The effects of SeNPs on the coloration and antibacterial properties of the leather material were evaluated. The results revealed that the NPs were mostly spherical in shape, regularly distributed, and closely anchored to the leather surface. The particle size distribution of SeNPs at concentrations of 25 mM and 50 mM was in the range of 36–77 nm and 41–149 nm, respectively. It was observed that leather/SeNPs exhibited a higher depth of shade compared to untreated ones, as well as excellent fastness properties. The results showed that leather/SeNPs can significantly enhance the antibacterial activity against model of bacteria, including Gram-positive bacteria (Bacillus cereus) and Gram-negative bacteria (Pseudomonas aeruginosa, Salmonella typhi and Escherichia coli). Moreover, the resulting leather exhibited low cytotoxicity against HFB4 cell lines. This achievement should be quite appealing to the footwear industry as a way to prevent the spread of bacterial infection promoted by humidity, poor breathability and temperature which promote the expansion of the microflora of the skin.

Microbiological and Chemical Analysis of Bamboo Textile Materials and Leathers Modified with Bamboo Extract at the Tanning Stage

In this paper, microbiological and chemical analysis were carried out in the case of bamboo textile materials and leathers modified by bamboo extract at the tanning stage. Microbiological resistance was examined for some fungi, i.e.: Aspergillus niger, Trichophyton mentagrophytes and Candida albicans and some bacteria strains: Escherichia coli, Salmonella enteritidis and Pseudomonas aeruginosa. In parallel, a safety analysis was conducted through the determination of heavy metals, certain aromatic amines and dimethyl fumarate. The main goal of the above-mentioned research was a comprehensive examination of materials which will be used as footwear components i.e.: linings, uppers and insoles. These issues are very important from the footwear manufacture point of view because of the opportunity to find new solutions in the field of hygienic and healthy materials which can be applied as footwear elements. The anti-microbial and anti-fungal resistance of materials are features important for the reduction of the probability of dermatosis. For this reason, they should be taken into account when the improvement of hygienic properties is pursued.

Preparation and Characterization of Nonwoven Fibrous Biocomposites for Footwear Components.

Chromium-tanned leathers used in the manufacture of footwear and leather goods pose an environmental problem because they contain harmful chemicals and are very difficult to recycle. A solution to this problem can be composite materials from tree leaves, fruit residues and other fibrous agricultural products, which can replace chromium-tanned leather. The present study describes the preparation of biocomposite leather-like materials from microbial cellulose and maple leave fibers as bio-fillers. The formulation was optimized by design of experiment and the prepared biocomposites characterized by tensile test, FTIR, DMA, SEM, adhesion test, volume porosity, water absorptivity, surface wettability and shape stability. From the viewpoint of future use in the footwear industry, results obtained showed that the optimized material was considerably flexible with tensile strength of 2.13 ± 0.29 MPa, elastic modulus of 76.93 ± 1.63 MPa and porosity of 1570 ± 146 mL/min. In addition, the material depicted good shape stability and surface adhesive properties. The results indicate that a suitable treatment of biomass offers a way to prepare exploitable nonwoven fibrous composites for the footwear industry without further burdening the environment.

Optimal footwear longitudinal bending stiffness to improve running economy is speed dependent

The primary footwear components of interest to improve performance are midsole material, weight, and longitudinal bending stiffness. Little is known about the effects of varied longitudinal bending stiffness across a range of running speeds. The purpose of this study was to identify changes in spatiotemporal variables, horizontal ground reaction forces, subjective comfort, and metabolic cost at different running speeds in response to varied longitudinal bending stiffness. Ten highly trained males ran at 14, 17 and 20 km/h in shoes with varying longitudinal bending stiffness (normal 5.9, stiff 10.5 and very stiff 17.0 N-m/rad). Ground reaction forces, metabolics and subjective comfort assessments were collected. There were significant changes (p < .05) in contact time, stride frequency, and stride length between shoe conditions at all three speeds. Peak propulsive force decreased with increased bending stiffness at all three speeds, but there was no change in braking or propulsive impulse. The patterns of changes in stride length and stride frequency were different between speeds. At 14 km/h, most participants elicited a minimum metabolic rate in the normal shoe. However, at 17 km/h an increased number of participants were more economical in the stiff shoe, despite it weighing an extra 50 g compared to the normal shoe. Running speed had an influence on subjective comfort, with participants tending to prefer the normal shoe at 14 km/h and the stiff shoe at 17 km/h. These results suggest that an optimal bending stiffness to reduce metabolic cost and improve comfort may be running speed dependent.

Panorama of natural fibers applied in Brazilian footwear: materials and market

Footwear material is of great importance mainly considering the user’s health. There are many components in contact with upper and mainly lower part of foot, being the sole essential part to weight distribution, muscle activity and vertebral column. This study aimed to verify how the natural fibers are applied at Brazilian market footwear, demonstrating the types of raw materials utilized, textile constructions and other variables. As well as comparing the information at natural fibers applications data from economics sources and material employment at the footwear international market. The methodology was based in literature research and interviews with Brazilian companies. The employment of natural fibers in footwear corresponds to a small part in comparison of synthetic fibers. Cellulosic fibers have been researched to reinforce rubbers and they are applied to sole as snow footwear. In addition, these fibers are being researched as biodegradable materials, showing innovations for instance, the use of leather waste, coconut fiber and latex, multilayers fabrics and finishing process adding bactericide properties to cotton. Brazilian footwear industry is finding solutions to reduce production costs in order to compete in the international market. One of the strategies is the gradual replacement of leather by fabrics, synthetic polymers and rubbers. The interviews identified the employment of cotton, raffia and jute fabrics especially in footwear summer collections. Thus, the increasing of researches about recycling footwear components and the development of biodegradable materials points a sustainability trend in this sector.

Balancing mixed-model assembly systems in the footwear industry with a variable neighbourhood descent method

This paper addresses new Mixed-model Assembly Line Balancing Problems (MALBP) in a real industrial context, the stitching systems of a footwear company. The work is part of large ongoing projects with this industry, and the main purposes are minimising the number of required workstations and smoothing the operators’ workload. The company has invested in new flexible automated assembly systems, which accommodate dozens of workstations and many moving boxes. Footwear components are inside boxes (with various quantities) which can move from the warehouses to a convenient workstation or between any workstations (in any order). This is a significant and distinct feature of the MALBP, together with the fact that the assignment of different skilled operators and machines is achieved simultaneously. An optimisation model is developed, in part to facilitate the understanding of the situation and to solve small-size instances. Due to the complexity of the problems, we had to devise an approximate method, based on the Variable Neighbourhood Descent (VND) metaheuristic and integrating an adaptation of the Ranked Positional Weighted (RPW) method. The adapted RPW method is used to create initial feasible solutions, while preassigning special operators and machines. After choosing good initial solutions, VND is applied to improve their quality. The new contributed method, named as RPW-VNDbal, is tested with medium and large instances, in two distinct stitching systems. A Lower Bound of the objective function and Simulation contribute to evaluate the solutions and their practicability. The results implemented by the project team, show that the RPW-VNDbal method is fast enough and offers better solutions than those implemented by the experienced operation managers of the company.

Biobased Additives as Biodegradability Enhancers with Application in TPU-Based Footwear Components

Biobased Additives as Biodegradability Enhancers with Application in TPU-Based Footwear Components

Study of 3D printing potential in supporting the manufacturing process of shoes for people with cerebral palsy

Currently, 3D printing is one of the most powerful manufacturing technologies. This study intends to analyse how 3D printing can support the manufacturing process of shoes' components for people with cerebral palsy. Three footwear components were considered: heel counter, metatarsalgia relief cushion, and sole. To assure the requirements for the aforementioned elements, people affected by cerebral palsy, orthopaedists, physiotherapists and experts in the production of orthopaedic shoes were consulted. Simultaneously, a WalkinSense dynamic gait test in a cerebral palsy patient was performed followed by the 3D-scanning of the feet. Subsequently, the required steps for a fully customised design were performed, resorting, when necessary, to mechanical behaviour verification through ABAQUS software; the final stage consisted in 3D printing tasks. A simple analysis to evaluate the production costs and users' satisfaction was also conducted. These case studies consist of a reliable starting point for defining new 100% customised footwear components manufacturing methodologies.

Scent properties by natural fragrance microencapsulation for footwear applications

AbstractThe aim of this study was to develop footwear materials and footwear packaging with scent properties using microencapsulated fragrances from essential oils. For that purpose, gelatine–carboxymethylcellulose (CMC) and melamine–formaldehyde (MF) resin‐based microcapsules containing limonene were synthesised using complex coacervation and in situ polymerisation processes, respectively. The microcapsules were characterised using various experimental techniques and applied to footwear materials (leather and textile) as well as to paperboard as packaging material to evaluate their performance. The microcapsule durability under various conditions, such as rubbing and ironing, was analysed in order to simulate shoe manufacturing and shoe wearing conditions. The characterisation of the synthesised microcapsules showed two different delivery behaviours. On the one hand, MF microcapsules are more resistant so they may be incorporated into footwear materials that have to be exposed to high mechanical and thermal stresses, such as linings. On the other hand, gelatine–CMC microcapsules should be incorporated into footwear components, such as insoles, which are exposed to lower stresses because they are less resistant and might not resist the process conditions. The combination of both kinds of microcapsules could ensure a rapid as well as a long‐lasting fragrance release. © 2015 Society of Chemical Industry

Patterns of mediolateral asymmetry in worn footwear

Background: Debate over footwear design and prescription is currently shaped by two opposing paradigms to which the clinician or researcher subscribes. Human structure is considered either ‘poor’ requiring intervention or ‘well-adapted’. The interventionist paradigm directs research on the effect of changing mediolateral footwear bias either within the shoe design or using inserts. However, the mediolateral condition of shoes worn by individuals has seldom been considered or measured.Objective: To describe a clinical assessment tool to measure outer-, mid- and innersole footwear components and report on patterns of mediolateral heel asymmetry in a sample of commonly used footwear.Main Outcome Measure: Total mediolateral asymmetry that includes the difference between medial and lateral outersole (mm), innersoles (mm) and mid- and innersole stiffness (Asker C).Results: A total of 212 shoes provided by 106 participants were assessed, with average shoe age 11.9 months (SD 11.4) and mean use 4.6 hrs.d−1 (SD 3.9). Shoe drop between 1.0 and 3.0 cm was measured in 87.8% of shoes. Zero or symmetrical wear was observed for 41.5% of shoes while 57.6% of shoes had 1 to 5 mm lateral heel degradation. The most frequent was 1 mm (30.2%) followed by 2 mm (12.3%) and 15.1% had 3 to 5 mm. Only 0.9% (2/212) had 1 mm of medial degradation. Asymmetry of wear was influenced by the reported age of the shoe, and females were likely to have greater lateral wear than men.Conclusions: Lateral heel degradation was the most frequently measured mediolateral asymmetry. Mediolateral asymmetry by design and/or degradation was measured in the outer-, mid- and innersoles. These results may be important for related footwear research on aberrant ankle and knee joint function.