Sustainable Reactive Polyurethane Hot Melt Adhesives Based on Vegetable Polyols for Footwear Industry

The aim of this work is to develop sustainable reactive polyurethane hot melt adhesives (HMPUR) for footwear applications based on biobased polyols as renewable resources, where ma-croglycol mixtures of polyadipate of 1,4-butanediol, polypropylene and different biobased polyols were employed and further reacted with 4-4′-diphenylmethane diisocyanate. The different reactive polyurethane hot melt adhesives obtained were characterized with different experimental techniques, such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), softening temperature and melting viscosity. Finally, their adhesion properties were measured from T-peel tests on leather/HMPUR adhesives/SBR rubber joints in order to establish the viability of the used biobased polyols and the amount of these polyols that could be added to reactive polyurethane hot melt adhesives satisfactorily to meet the quality requirements of footwear joints. All biobased polyols and percentages added to the polyurethane adhesive formulations successfully met the quality requirements of footwear, being comparable to traditional adhesives currently used in footwear joints in terms of final strength. Therefore, these new sustainable polyurethane adhesives can be considered as suitable and sustainable alternatives to the adhesives commonly used in footwear joints.

Joining sheets made from dissimilar materials by hole hemming

This research work presents a new joining process based on the hemming process for attaching sheets made from dissimilar materials with very different mechanical properties. The process is termed ‘hole hemming’ and consists in producing a mechanical interlock between pre-drilled holes which can be made anywhere on the sheets. The process is carried out in a two-stage operation including flanging the hole of an outer sheet and bending the flange over the hole of an inner sheet. First, the joining stages and the required tools are designed. Then, the joining of DP780 steel and AA6061-T6 aluminium alloy sheets, which are applied to manufacture lightweight structures in the automotive industries, is investigated using finite element analysis. Results show that the hole hemming process is able to successfully join these materials without fracture. The hole-hemmed joint withstood the maximum forces of 2.5 and 0.5 kN in single-lap shear and peel tests, respectively, and failed with hole bearing mode which is known as a gradual failure mode. The results demonstrate the applicability of the hole hemming process for joining dissimilar materials.

Delamination Testing of AlSi10Mg Sandwich Structures with Pyramidal Lattice Truss Core made by Laser Powder Bed Fusion

Sandwich structures possess a high bending stiffness compared to monolithic structures with a similar weight. This makes them very suitable for lightweight applications, where high stiffness to weight ratios are needed. Most common manufacturing methods of sandwich structures involve adhesive bonding of the core material with the sheets. However, adhesive bonding is prone to delamination, a failure mode that is often difficult to detect. This paper presents the results of delamination testing of fully additive manufactured (AM) AlSi10Mg sandwich structures with pyramidal lattice truss core using Laser Powder Bed Fusion (LPBF). The faces and struts are 0.5 mm thick, while the core is 2 mm thick. The inclination of the struts is 45°. To characterise the bonding strength, climbing drum peel tests and out-of-plane tensile tests are performed. Analytical formulas are derived to predict the expected failure loads and modes. The analytics and tests are supported by finite element (FE) calculations. From the analytic approach, design guidelines to avoid delamination in AM sandwich structures are derived. The study presents a critical face sheet thickness to strut diameter ratio for which the structure can delaminate. This ratio is mainly influenced by the inclination of the struts. The peel tests resulted in face yielding, which can also be inferred from the analytics and numerics. The out-of-plane tensile tests didn’t damage the structure.

Characterisation of the opening behavior of multilayer films with cohesive failure mechanism by in situ peel tests in the ESEM

In this work, peel tests inside the chamber of an ESEM ( in situ peel tests) are described with heat-sealed test specimens of packaging systems made of multilayer films that simulate different flexible packaging types, according to the packaging line used. The in situ peel tests provided evidence to describe the influence of three different main aspects of the packaging process in relation to the opening behavior of the sealing packages. The investigated aspects are the peel angle, the alignment angle between the orientation of the multilayer films and the seal, and the bulge formation as a consequence of inadequate sealing parameters. In situ peel tests enabled the differentiation between peel angle and local (micro) peel angle, which results from the overall stiffness of the multilayer structure film. Alignment angles of 90° and 45° were found to produce similar opening forces. Images showing the formation of various new local micro fissures on new planes during the in situ peel test explained how the opening force can be dramatically increased during the tearing of two sealed multilayer films.

Enhancement of Adhesion Characteristics of Low-Density Polyethylene Using Atmospheric Plasma Initiated-Grafting of Polyethylene Glycol

The low-density polyethylene/aluminum (LDPE/Al) joint in Tetra Pak provides stability and strength to food packaging, ensures protection against outside moisture, and maintains the nutritional values and flavors of food without the need for additives in the food products. However, a poor adhesion of LDPE to Al, due to its non-polar surface, is a limiting factor and extra polymeric interlayers or surface treatment is required. Plasma-assisted grafting of the LDPE surface with different molecular weight compounds of polyethylene glycol (PEG) was used to improve LDPE/Al adhesion. It was found that this surface modification contributed to significantly improve the wettability of the LDPE surface, as was confirmed by contact angle measurements. The chemical composition changes after plasma treatment and modification process were observed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). A surface morphology was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Adhesion characteristics of LDPE/Al adhesive joints were analyzed by the peel tests. The most significant adhesion improvement of the PEG modified LDPE surface was achieved using 10.0 wt.% aqueous (6000 M) PEG solution, while the peel resistance increased by approximately 54 times in comparison with untreated LDPE.

Delamination Testing of Additive Manufactured Sandwich Structures with Lattice Truss Core

Sandwich structures possess a high bending stiffness compared to monolithic structures with a similar weight. This makes them very suitable for lightweight applications where high stiffness to weight ratios are needed. Most common manufacturing methods of sandwich structures involve adhesive bonding of the core material with the sheets. However, adhesive bonding is prone to delamination, a failure mode which is often difficult to detect. In this paper, the results of delamination testing of fully additive manufactured (AM) AlSi10Mg sandwich structures with pyramidal lattice truss core are presented. To characterise the bonding strength, climbing drum peel tests and out-of-plane tensile tests are done. The thickness of the faces and the diameter of the struts is 0.5 mm, while the core is 2 mm thick. The inclination of the struts is 45°. To predict the expected failure loads and modes, analytical formulas are derived. The analytics and tests are supported by finite element (FE) calculations. From the analytic approaches, design guidelines to avoid delamination in AM sandwich structures can be followed. The study shows, that critical ratios for face sheet thickness to strut diameter can be determined, to define if the structure tends to delaminate under certain loads. Those ratios are mainly influenced by the strut inclination. The peel tests resulted in face yielding, which can also be followed from the analytics and numerics. The out-of-plane tensile tests didn't damage the structure.

Development and testing of material extrusion additive manufactured polymer–textile composites

The adoption of Additive Manufacturing (AM) has gradually transformed the fashion industry through innovation and technology over the last decade. Novel AM systems and techniques are continuously being developed, leading to the application of AM polymers with textiles and fabrics in the fashion industry. This work investigates the development and testing of polymer–textile composites using polylactic acid (PLA) filaments on synthetic mesh fabrics using direct material extrusion (ME). An aspect of this paper highlights the appropriate combination of printing material, textile substrate, and printer settings to achieve excellent polymer–textile adhesion. Details of the printing process to create polymer–textile composites are described, as are the interfacial strength results of the T-peel tests, and the observed failure modes post-testing. The peel strengths for different ME bonded polymer–textile composites are examined and used to identify the compatibility of materials. This work visualised the potential of direct ME of polymers onto textile fabrics as a material-joining approach for new textile functionalisation, multi-material composite explorations and innovative aesthetic print techniques. This work also adds to the limited knowledge of AM polymer–textile composites, which can provide helpful information for designers and researchers to develop new applications and facilitate future research development in smart embedded and programmable textiles.

Identification of Factors Affecting the Strength of Joints in Steel-Titanium-Aluminium Composites in Monotonic Peel Tests

The paper presents the results of strength tests (ram test) of two types of three-layer material made using the explosion welding technology. Clad materials used in the test differed in the overlay layer (A1050 and A3003). The results were analysed for factors affecting the obtained level of joint strength.