Comparison of Polylactide-Based Active Films Containing Berberine and Quercetin as Systems for Maintaining the Quality and Safety of Blueberries.

Polymeric thin films based on polylactide with an addition of poly(ethylene glycol) as a plasticizer and flavonoids in the form of quercetin and berberine were subjected to tests that were particularly relevant from the point of view of contact with food. A comparative analysis of the effect of individual flavonoids on the antioxidative properties of tested films and blueberry storage was carried out. The influence of active compounds on the water vapor permeability, as well as UV protection, of the obtained materials was investigated. Also, the specific migration of individual flavonoids from obtained materials to food simulants in the form of acetic acid and ethyl alcohol was determined. The crucial point of this study is the storage of blueberries. The obtained results indicate that the selection of packaging, containing individual active compounds, depends on the purpose and requirements that the packaging must meet for particular types of food.

Properties and Performance of Epoxy Resin/Boron Acid Composites.

This research study focused on the effect of adding boric acid to epoxy resin in order to obtain a composite material with improved properties and performance. To this end, a fine powder of boric acid (H3BO3) was introduced into epoxy resin in different amounts, i.e., 0.5 g, 1.0 g, and 1.5 g. As the matrix of the epoxy composites, styrene-modified epoxy resin based on bisphenol A (BPA) (Epidian 53) was used. It was cross-linked with two types of curing agents, i.e., an amine (ET) and a polyamide (PAC). The mechanical properties of the obtained epoxy composites (in terms of compressive strength, compressive modulus, and compressive strain) were determined at room temperature in order to assess the effect of the addition of boron acid and of the type of curing agent employed to cure the epoxy on these characteristics. Calorimetric measurements were made to highlight any changes in the glass transition temperature (Tg) as a result of the addition of boric acid to epoxy resin. Finally, flammability tests were performed on both Epidian 53/PAC and Epidian 53/ET epoxy composites to analyze their fire behavior and consequently establish the effectiveness of the selected additive as a flame retardant.

Mechanical Properties of Epoxy Compounds Based on Unmodified Epoxy Resin Modified with Boric Acid as an Antiseptic.

The objective of this study was to compare the selected mechanical properties of epoxy compounds based on an unmodified epoxy resin with those containing an antiseptic as a modifying agent. Experiments were carried out on twelve epoxy compounds made of an epoxy resin based on bisphenol A (BPA) with a basic epoxide amount of 0.48-0.51 mol/100 g. Three curing agents were used: one polyamide (a polyaminoamide curing agent) and two amines (one was an adduct of aliphatic amine and aromatic glycidyl ether, and the other was an adduct of cycloaliphatic amine). The epoxy compounds were modified by adding an antiseptic in the form of powdered boric acid (H3BO3) in three amounts: 0.5 g, 1.0 g, and 1.5 g. The cured modified and unmodified epoxy compounds were subjected to compressive strength testing and microscopic examination. The experimental results showed that the epoxy compounds containing adduct of aliphatic amine (triethylenetetramine) and aromatic glycidyl ether as the amine curing agent, i.e., E5/ET/100:18, had the highest compressive strength out of all the tested epoxy compounds, with the highest value of 119 MPa obtained for the epoxy compound modified by the addition of 1.0 g boric acid. The epoxy compounds modified with boric acid acquired antiseptic properties and, for most cases, exhibited a higher compressive strength than the unmodified epoxy compounds (not lower than that specified by the manufacturer for unmodified epoxy compounds).

Modification of Epoxides with Metallic Fillers-Mechanical Properties after Ageing in Aqueous Environments.

The aim of this research was a comparative analysis of selected mechanical properties of epoxy compounds that were modified with metallic fillers and aged in aqueous environments. The tested epoxy compounds consisted of three components: styrene modified epoxy resin based on Bisphenol A, triethylenetetramine curing agent (resin/curing agent ratio of 100:10) and two types of metallic fillers in the form of particles: aluminum alloy (EN AW-2024-AlCu4Mg1) and tin-phosphor bronze (CuSn10P). Samples were subjected to ageing in 4 water environments: low-, medium- and high-mineralized natural water and in a sugar-containing solution for 1, 2 and 3 months. The epoxy samples were subjected to compressive strength tests in accordance with the ISO 604:2002 standard. It was observed that, among others, the compositions seasoned in low-mineralized water usually achieved the highest average compressive strength. As for filler type, using the bronze filler (CuSn10P) usually achieved the highest average compressive strength results.

Identification of the Production of Small Holes and Threads Using Progressive Technologies in Austenite Stainless Steel 1.4301.

This article focuses on the technologies used by a manufacturing company to produce threads in chrome-nickel steel 1.4301 at specific sheet thicknesses. To enhance production quality, two specific technologies were chosen for hole formation, considering the requirements of the company. Both conventional drilling and nonconventional laser cutting methods were evaluated as potential techniques for hole production. Conventional thread-cutting technology and progressive forming technology were employed to create metric internal threads. The aim of integrating these diverse technologies is to identify the optimal solution for a specific sheet thickness in order to prevent the occurrence of defective threads that could not fulfil the intended purpose. The evaluation of the threads and holes relies on the examination of surface characteristics, such as the quality of the surface, as well as the lack of any signs of damage, cracks, or burrs. Furthermore, residual stresses in the surface layer were monitored because these stresses have the potential to cause cracking. Additionally, extensive monitoring was performed to guarantee that the form and size of the manufactured threads were correct to ensure smooth assembly and optimal functionality.

Biological Effects and Toxicity of Compounds Based on Cured Epoxy Resins.

The aim of this work was to investigate selected biological and toxicity properties of cured epoxy resin-based compounds based on a bisphenol A epoxy resin, cold-cured by a polyamide and containing two types of metal powders (aluminum and copper). This study involved cytotoxicity analysis, pH measurements, absorbance measurements and sterilization. The cytotoxicity analysis was conducted to determine the harmful degree of the cured epoxy resin. Aimed at identifying toxic agents in cured compounds, the cytotoxicity analysis involved absorbance measurements in an entire wavelength range. Cytotoxicity and absorbance results demonstrated that the extracts of all the tested resin samples had no cytotoxic effects on the cells of living organisms. The absorbance values obtained over the entire wavelength range did not point to the formation of aggregations, which proved that no toxic agents harmful to living organisms were extracted from the resin samples. Based on the results obtained, it can be concluded that all tested compounds, based on epoxy resins, which are also used as adhesives in various applications, are essentially safe materials when using such formulations in a cured state.

Influence of Physical Modification of the Adhesive Composition on the Strength Properties of Aerospace Aluminum Alloy Sheet Adhesive Joints.

One of the most important design factors in the constitution of adhesive joints is the correct choice of adhesive. Currently, there is a full range of options on the commercial market in this regard, but there is increasing research into modifying adhesives for specific engineering applications. The aim of this study was to analyze the effect of physical modification with fillers on the properties of the adhesive composition and the adhesive joints. The adhesives used in the study were a composition of Epidian 5 epoxy resin and PAC curing agent modified with 1% montmorillonite, 5% calcium carbonate and 20% activated carbon. The adhesive compositions in the cured state were subjected to strength tests and SEM and DSC analyses. Using these compositions, adhesive joints of EN AW 2024 T3 aluminum alloy sheets were also made. The tests carried out showed that, due to the use of different fillers, their effects on certain properties of the adhesive compositions are different types. It was shown that physical modification of the adhesive composition does not always result in positive effects. The study also attempted to determine the correlation between the properties of the adhesive compositions in the cured state and the strength of the adhesive joints.

Investigation of the Surface Roughness and Surface Uniformity of a Hybrid Sandwich Structure after Machining.

The parameters of surface roughness Ra, Rz and Rmax as well as surface topography Sa, Sz, Sp and Sv of the two-layer sandwich structure composed of an AW-2024 T3 aluminum alloy (Al) and a carbon-fiber-reinforced polymer (CFRP) were measured to determine an impact of the machining configuration (arrangement of the materials forming a sandwich structure) and the type of tool (presence of the tool coating) on the quality of the surface obtained through circumferential milling. The measurements revealed that milling produced different values of surface roughness for the aluminum alloy and the CFRP composite with values of 2D and 3D surface roughness being higher for the composite layer. The highest value of Ra of 1.10 µm was obtained for the surface of the CFRP composite using the CFRP/Al configuration and a TiAlN-coated tool. The highest values of the Rz (6.51 µm) and Rmax (8.85 µm) surface roughness parameters were also obtained for the composite layer using the same machining configuration and type of tool.

Assessment of Surface Treatment Degree of Steel Sheets in the Bonding Process.

The aim of the paper is to determine the influence of the surface treatment on the adhesive properties of steel sheet surfaces and the strength of the adhesive joints of steel sheets. The paper also aims to assess the degree of steel sheets' surface treatment in the bonding process. Due to the many methods of surface treatment and types of materials, the assessment of the surface treatment method is extremely important in adhesive processes. Two variants of the surface treatment were used: without a paint coating and with a paint coating, divided into two groups (without degreasing and with degreasing). Additionally, in the case of the analysis of the steel samples without the paint coating, mechanical treatment was applied. Two-component epoxy adhesive, prepared on the basis of bisphenol A and a polyamide curing agent, was used to prepare the single-lap adhesive joints of the steel sheets. The tests determined: (i) the adhesive properties of the steel sheets' surface based on the measurement of the contact angle of polar and apolar liquids (including wettability, work of adhesion, and surface free energy), (ii) surface roughness parameters (PN EN ISO 4287), and (iii) mechanical properties (load capacity and shear strength) of the steel sheets' adhesive joints (EN DIN 1465). Contact angle measurements of the steel sheet surfaces showed that the polar liquid better reflects the obtained strength results of the analyzed adhesive joints than the apolar liquid. Furthermore, better wettability of the surface of steel sheets with both polar and apolar liquids was obtained for samples whose surface was subjected to degreasing. It can also be concluded that the wettability of the surface can be used as one of the indicators of the degree of the surface treatment for the bonding process.

Effect of Diluents on Mechanical Characteristics of Epoxy Compounds.

The aim of this work is to assess the influence of different commercial diluents on some mechanical properties of two bisphenolic epoxy compounds, cold-cured by a polyamide curing agent, to be employed as epoxy structural adhesives for building and industrial applications. The diluents under analysis were epoxy, bituminous, nitro, acrylic and extraction. The choice of these products was made on the basis of their wide commercial availability as diluents for epoxies used as adhesives and in different industrial and construction applications. The diluents were all added in small proportions, i.e., from 1 to 10 g per 100 g of epoxy resin. The cold-cured epoxy compounds were subjected to compressive (according to ISO 604) and static tensile (according to ISO 527-1) tests. The same mechanical tests were performed on both unmodified epoxy resins, for comparison purposes. On the basis of the obtained results, it was concluded that the influence of the presence of a diluent, and of its amount, on the mechanical properties of epoxy compounds depends on the type of resin and of diluent, as well as on the mechanical characteristics analyzed.

Polylactide-Based Films Incorporated with Berberine-Physicochemical and Antibacterial Properties.

A series of new polymeric materials consisting of polylactide (PLA), polyethylene glycol (PEG) and berberine chloride (B) was evaluated. PEG was incorporated into the polymer matrix with the aim of obtaining a plasticizing effect, while berberine was added in order to obtain antibacterial properties in formed packaging materials. Materials were formed using the solvent-casting procedure. Fourier transform infrared spectroscopy and scanning electron microscopy were used so as to establish the structural changes resulting from the introduction of berberine. Thermogravimetry and differential scanning calorimetry were applied to study the thermal properties. Further, mechanical properties and differences in colour and transparency between the control sample and films containing berberine were also studied. The recorded data indicates that berberine formed a network on the surface of the PLA-based materials. Introduction of an active compound significantly improved thermal stability and greatly affected the Young's modulus values of the studied polymeric films. Moreover, it should be stressed that the addition of the studied active compound leads to an improvement of the antibacterial properties, resulting in a significant decrease in growth of E. coli and the S. aureus bacteria cultures.

The Influence of Sandblasting Process Parameters of Aerospace Aluminium Alloy Sheets on Adhesive Joints Strength.

In this study, the influence of sandblasting process parameters as a surface preparation method on the strength of single-lap adhesive joints of EN AW 2024 T3 aerospace aluminium alloy sheets was determined. Eleven sets of sandblasting parameters were used, which were determined according to a determined experimental plan. The variable factors in the sandblasting process were pressure, nozzle distance, and workpiece displacement speed. The sand jet incidence angle was constant. Garnet 80 E+ was the abrasive material that was used. The joints were made using an epoxy adhesive composition of Epidian 5 epoxy resin and a PAC curing agent. The influence of the surface preparation method on the surface roughness and contact angle to determine the surface free energy was evaluated. The shear strength of the adhesive joints was also determined, which finally allowed the evaluation of the applied surface treatment variants. The obtained results were subjected to statistical analysis, which indicated that the highest shear strength of the adhesive joints was obtained for samples whose surfaces were treated by sandblasting at parameter configurations in which the pressure was 5-6 × 105 Pa; the distance between the nozzle and the sandblasted surface should not be greater than 97 mm, and the speed at which the workpiece moves in relation to the nozzle should not be greater than 75 mm/min.

Surface Roughness after Milling of the Al/CFRP Stacks with a Diamond Tool.

This study presents the results of research on the surface quality of hybrid sandwich structures after milling with a diamond blade tool. It identifies the effects of feed and machining strategy on the roughness and topography of the surface. It provides an analysis of Ra and Rz surface roughness parameters as well as Sp, Sz, and Sv surface topography parameters. The processed object was a two-layer sandwich structure consisting of aluminium alloy 2024 and CFRP (carbon fibre-reinforced polymer) composite. The minimum values of the Ra and Rz surface roughness parameters were obtained on the aluminium alloy surface, whereas the maximum values were obtained on the CFRP surface. The same was true for the 3D surface roughness parameters-the lowest values of Sp, Sz, and Sv parameters were obtained on the surface of the metal layer, while the highest values were obtained on the surface of the composite layer (the maximum value of the Sp parameter was an exception). A surface topography analysis has revealed a targeted and periodic pattern of micro-irregularities for the vast majority of the samples considered. The statistical analysis shows that the surface roughness of the aluminium alloy was only affected by the feed rate. For the CFRP, the feed rate and the interaction of milling strategy and feed rate (S × fz) had a statistically significant effect. The obtained results provide a basis for designing such sandwich element processing technology, for which differences in roughness and topography parameters for the component materials are lowest.

Influence of Surface Treatment on Steel Adhesive Joints Strength-Varnish Coats.

The purpose of the paper is to determine the impact of surface treatment on the strength of adhesive joints, made from various steel sheets. Two variants of the surface treatment steel adherends were used: without the varnish coat and with the varnish coat, using three polymer-based varnishes (a simple, a hybrid, and a gel). Two types of the adhesives were used to prepare the adhesive joints: a single-component cyanoacrylate adhesive and a two-component epoxy adhesive. A strength test of the adhesive joints (EN DIN 1465 standard), a coating adhesion test (ASTM D3359-B standard), and surface topography, as well as surface roughness, parameters (PN-EN ISO 11562, PN-EN ISO 4287, and PN-EN ISO 25178 standards) were used. Based on the strength tests, it was observed that the adhesive joints, with the hybrid varnish onto the adherend's surface, achieved markedly lower shear strength. The best results, in terms of the adhesive joint strength, made using the cyanoacrylate adhesive were achieved for the joints where the adherends were coated with a simple varnish, while in the joints made using the epoxy adhesive, the highest shear strength was achieved by the joints of sheets whose surfaces were coated with the gel varnish.

Antibacterial Films Based on Polylactide with the Addition of Quercetin and Poly(Ethylene Glycol).

A series of new films with antibacterial properties has been obtained by means of solvent casting method. Biodegradable materials including polylactide (PLA), quercetin (Q) acting as an antibacterial compound and polyethylene glycol (PEG) acting as a plasticizer have been used in the process. The effect of quercetin as well as the amount of PEG on the structural, thermal, mechanical and antibacterial properties of the obtained materials has been determined. It was found that an addition of quercetin significantly influences thermal stability. It should be stressed that samples containing the studied flavonoid are characterized by a higher Young modulus and elongation at break than materials consisting only of PLA and PEG. Moreover, the introduction of 1% of quercetin grants antibacterial properties to the new materials. Recorded results showed that the amount of plasticizer did not influence the antibacterial properties; it does, however, cause changes in physicochemical properties of the obtained materials. These results prove that quercetin could be used as an antibacterial compound and simultaneously improve mechanical and thermal properties of polylactide-based films.

Cold-Cured Bisphenolic Epoxy Adhesive Filled with Low Amounts of CaCO3: Effect of the Filler on the Durability to Aqueous Environments.

The effects of aging exposures to three non-saline aqueous environments on the compressive mechanical properties of a calcium carbonate-filled bisphenolic epoxy adhesive, cold-cured with the addition of two curing agents suitable for the cure at ambient temperature (i.e., Mannich base and triethylenetetramine), were assessed. The amount of the added filler (CaCO3) varied from 1 to 3 g per 100 g of resin; the immersion times in each of the selected medium varied from 1 to 10 months. It was found that the mechanical properties measured in compression mode on cylindrical specimens of unfilled and CaCO3-loaded epoxy were scarcely influenced by the kind of curing agent employed; only the compressive modulus was limitedly affected by this parameter. Referring to the behavior when aged in water, the CaCO3-filled epoxies displayed noticeable growths in modulus, small reductions in strength, and limited variations in strain, with a certain influence of the exposure time, especially when comparing the properties at the lowest time with those at medium-long times. On the basis of the results of statistical MANOVA analysis, it can be concluded that among the compositional factors (i.e., the type of curing agent employed to cure the epoxy compounds and the micro-filler content), only the amount of CaCO3 filler significantly affects the compressive modulus.

Mechanical Properties of Epoxy Compounds Based on Bisphenol a Aged in Aqueous Environments.

(1) Background: The aim of the work is to determine the influence of selected aqueous environments of various types of liquids on the strength of adhesive compositions prepared from epoxy resin based on bisphenol A combined with two different curing agents: tritethylenetetramine and polyaminoamide C. (2) Methods: The cured epoxy adhesive compounds samples were seasoned in four aqueous environments of the liquid: rainwater, demineralized water, tap water, and a sweetened drink. Three variants of the aging time in the above-mentioned operating environments were adopted: one month, two months, and three months. After the specified maturing time, samples of epoxy adhesive compositions were subjected to the strength tests on the Zwick/Roell 150 testing machine, which is in accordance with ISO 604 standard, determining the compressive strength. (3) Results: On the basis of the obtained strength test results and their analysis, it was noticed, inter alia, that the strength of the epoxy compounds decreases with the aging time in all used aqueous environments. Moreover, in the case of both types of the epoxy compounds, the highest strength was achieved after aging in demineralized water.

The Influence of Mixing Methods of Epoxy Composition Ingredients on Selected Mechanical Properties of Modified Epoxy Construction Materials.

The proper process of preparing an adhesive composition has a significant impact on the degree of dispersion of the composition ingredients in the matrix, as well as on the degree of aeration of the resulting composition, which in turn directly affects the strength and functional properties of the obtained adhesive compositions. The paper presents the results of tensile strength tests and SEM microphotographs of the adhesive composition of Epidian 57 epoxy resin with Z-1 curing agent, which was modified using three fillers NanoBent ZR2 montmorillonite, CaCO3 calcium carbonate and CWZ-22 active carbon. For comparison purposes, samples made of unmodified composition were also tested. The compositions were prepared with the use of six mixing methods, with variable parameters such as type of mixer arm, deaeration and epoxy resin temperature. Then, three mixing speeds were applied: 460, 1170 and 2500 rpm. The analyses of the obtained results showed that the most effective tensile results were obtained in the case of mixing with the use of a dispersing disc mixer with preliminary heating of the epoxy resin to 50 °C and deaeration of the composition during mixing. The highest tensile strength of adhesive compositions was obtained at the highest mixing speed; however, the best repeatability of the results was observed at 1170 rpm mixing speed. Based on a comparison test of average values, it was observed that, in case of modified compositions, the values of average tensile strength obtained at mixing speeds at 1170 and 2500 rpm do not differ significantly with the assumed level of significance α = 0.05.

Effect of Polymer Additives on the Microstructure and Mechanical Properties of Self-Leveling Rubberised Concrete.

The materials based on concrete with an addition of rubber are well-known. The interaction between concrete components and rubber particles is in the majority cases insufficient. For this reason, different substances are introduced into concrete-rubber systems. The aim of this paper is to establish the influence of five different polymer additives, i.e., 1. an aqueous dispersion of a styrene-acrylic ester copolymer (silanised) (ASS), 2. water dispersion of styrene-acrylic copolymer (AS), 3. anionic copolymer of acrylic acid ester and styrene in the form of powder (AS.RDP), 4. water polymer dispersion produced from the vinyl acetate and ethylene monomers (EVA), 5. copolymer powder of vinyl acetate and ethylene (EVA.RDP)) on the properties of the self-leveling rubberised concrete. Scanning electron microscopy has allowed to establish the interaction between the cement paste and rubber aggregates. Moreover, the compressive strength and flexural strength of the studied materials were evaluated. The results indicate that the mechanical properties depend extensively on the type as well as the amount of the polymer additive introduced into the system.

The Impact of the Acidic Environment on the Mechanical Properties of Epoxy Compounds in Different Conditions.

The aim of this work was to determine the impact of the acidic environment on the mechanical properties of two epoxy compounds in different conditions. The samples were made from the epoxy compounds composed of the epoxy resin (based on Bisphenol A), triethylenetetramine curing agent (unmodified compound), and calcium carbonate (CaCO3) (modified compound). The epoxy compound samples were seasoned for the following period of time (i.e., one week, one month, and three months). The environment was tap water and the acidic environment had three different concentrations of acetic acid (3%, 6%, and 9%). Strength tests of the epoxy compound samples were carried out in accordance with the ISO 604 standard. In the case of the modified composition, it is noted that the samples immersed in tap water were characterized by a higher strength than in acidic environments. A similar tendency was observed for unmodified compositions, although the differences were smaller than for the modified compositions. It was also noticed that the increase in the pH of the acidic solution in many analyzed cases contributed to the decrease in mechanical properties, although the immersion time in the acidic solution is important.