Quantifying Adhesive Strength of Tapes Through Precision TAA Method

Abstract

Tapes are widely utilized across various industries, offering versatile solutions for bonding, sealing, and packaging applications. Their ease of use, strength, and adaptability make them essential in manufacturing, construction, and consumer markets. However, the effectiveness of tapes depends heavily on their adhesive performance, which is influenced by factors such as the adhesive layer composition, material compatibility, environmental conditions, and contact parameters. Quantifying adhesive performance through standardized testing is critical to ensuring reliability, optimizing functionality, and meeting industry-specific requirements. Traditional methods, such as peel and shear tests, are commonly used to evaluate the adhesive and shear strength of tapes. However, these methods typically operate at macro-load scales and often use complex sample geometries and significant material quantities. Recently, precision indentation–retraction testing has emerged as a promising technique for accurately quantifying the adhesion and cohesion forces of viscoelastic fluids. This study adapts this method to evaluate and compare the adhesive strength of various commercially available adhesive tapes. The adhesion force and separation energy of five commercial tapes, namely paper masking tape, high-temperature tape, insulation tape, duct tape, box wrapping tape, and double-sided tape, were measured using a Falex Tackiness Adhesion Analyser (TAA) tester, under controlled conditions (approach speed: 0.01 mm/s, retraction speed: 0.1 mm/s, and load: 50 mN). The results indicated that the adhesion force and separation energy varied significantly among the tapes, whereas a different pattern in the indentation–retraction curves was obtained for these tapes. In addition, the significance of difference among the adhesive properties of the tapes was assessed with the use of analysis of variance (ANOVA). This innovative approach not only enhances the precision of adhesive strength measurements but also provides valuable insights into adhesive layer properties, offering a novel tool for research, development, and quality control in tape production.

1. Introduction

Adhesive tapes are versatile composite materials designed to join surfaces through a pressure-sensitive adhesive (PSA) layer applied to a backing film [1]. PSAs are viscoelastic polymers, which exhibit both liquid-like flow and solid-like resilience under pressure [2]. This combination enables PSAs to form bonds without additional activators like heat or solvents, distinguishing them from other adhesive types [3]. The adhesion mechanism primarily relies on a balance between adhesive and cohesive forces, with adhesive forces binding the tape to the surface and cohesive forces maintaining the integrity of the adhesive layer. These interactions are governed by Van der Waals forces, hydrogen bonding, and, occasionally, covalent bonding, depending on the adhesive chemistry and the substrate involved [4].

Several factors influence the strength, durability, and functionality of adhesive tapes, including adhesive composition, backing material, surface energy, and environmental conditions [5]. PSAs are generally composed of elastomers (like natural rubber or synthetic acrylics), tackifiers, and plasticizers, each contributing distinctively to the adhesive’s properties [6]. Rubber-based adhesives offer high initial tack, allowing for immediate grip, but may degrade over time, especially under UV exposure [7]. Acrylic-based adhesives, on the other hand, are resistant to temperature changes, oxidation, and UV light, making them ideal for high-durability applications [8]. The effectiveness of adhesive bonding also depends on the PSA layer’s interaction with the substrate surface, often influenced by surface energy [9]. For example, high-energy surfaces like metals and glass better promote wetting by the adhesive, enhancing molecular interactions and bond strength. Conversely, low-energy surfaces like polyethylene and polypropylene generally require surface treatments or specialized adhesives for effective bonding. In addition, adhesion mechanics involve PSA flowing under pressure into microscopic surface asperities, increasing the effective contact area and enhancing bond strength through both mechanical interlocking and molecular attraction [10]. These properties enable adhesive tapes to maintain robust bonds even under moderate shear stress or tension.

In everyday life, adhesive tapes play crucial roles across industries [11], including electronics, construction, healthcare, and automotive, each requiring tailored adhesive properties. In electronics, tapes must provide electrical insulation, thermal stability, and outgassing resistance. Double-sided tapes are frequently used in microelectronics to bond components, providing high shear strength while reducing assembly weight. Medical tapes in healthcare must be biocompatible, hypoallergenic, and secure on dynamic surfaces like skin, which can stretch and contract. Silicone or hydrocolloid adhesives minimize irritation and allow for clean removal. Automotive tapes, by contrast, must withstand vibration, moisture, and temperature extremes. Polyurethane or acrylic adhesive formulations are commonly used here for their resilience and ability to maintain adhesive strength in challenging environments.

To ensure sufficient adhesive performance, several methods are used to measure the adhesion of tapes by quantifying peel strength, tackiness, and shear resistance. Peel testing [12,13] is one of the most common methods that is being used to measure the force required to peel a tape from a substrate at a specific angle, usually 90° or 180°. This test provides insights into how the adhesive bonds over a specified contact area, as described in ASTM D3330, which is essential for the standardization of PSAs. In industry, typically, peel tests are combined with shear testing [14,15], which assess the adhesive’s resistance to forces parallel to the surface, indicating its holding power under continuous load. In a typical shear test, a strip of tape is applied to a vertical surface with a known weight attached, measuring the time it takes for the tape to detach under gravity. ASTM D3654 outlines standards for shear testing, which is essential for applications that require high durability under constant stress, like in automotive and construction applications.

Recently, new techniques for measuring adhesion emerged. Among them, tack testing [16,17] is gaining in popularity. These tests are used to evaluate the “stickiness” of the tape when contacting and subsequently being pulled apart from a surface. Tack tests include the loop tack test [16], in which a looped piece of tape is pressed onto a surface and then removed, and the probe tack test [17], in which a small probe is pressed onto the adhesive layer for a predetermined time and load and then pulled back to measure the resistance force (which also correlates to the adhesion force). These tack measurement methodologies have also reached standardization, for example ASTM D2979-16 (probe tack test, although withdrawn and no longer supported) and ASTM D6195-03 (loop tack test).

However, these standardized methods operate under high applied loads (N—kN) and are not sensitive enough to differentiate between small changes in, e.g., PSA layer formulations. Thus, there is a need for the development of versatile and sensitive test methods that will assist in further development of new adhesives. Recently, in the lubricants industry, a new method was developed to measure the adhesion and tackiness of greases onto surfaces [18]. However, there is a clear difference in what is conceived as tacky and adhesive between the grease and adhesive industry. In greases, tackiness is considered as the ability of a grease to form threads (measured as the maximum thread length), and adhesion is its ability to adhere onto a surface (measured as the maximum force on retraction). On the other hand, in adhesives, tackiness and adhesion are regarded as the same, both measured by the maximum force required for separation. This new test method resembles probe tack testing as it is also based on an indentation–retraction procedure. However, this method uses high precision load-displacement sensors (load cells of maximum 100 mN, having a resolution of 1/1.000), that allow for accurate and repeatable measurements [19]. In addition, the contacting materials (tape and counter material) and contact conditions (applied load, indentation and retraction speed, contact time, temperature, etc.) can easily be changed to simulate different adhesion systems. Since August 2024, it has become a standardized method (ASTM D 8576-24) for measuring the thread length and pull-off force of lubricating greases. This approach offers distinct advantages over conventional methods, particularly in terms of sensitivity to subtle variations in adhesive properties, which are often undetected by standard peel or shear tests. Furthermore, the ability to easily adjust experimental conditions, such as contact geometry and applied load, makes it a versatile and scalable method suitable for evaluating a wide range of adhesive materials and applications.

The aim of this work is to expand the use of this high-precision method to adhesives. This first work demonstrates the feasibility of the method by measuring the adhesion force of commercially available tapes and analyzing their indentation–retraction patterns. From the authors’ point-of-view, this new method will assist in the formulation of better adhesive layers and offer insights into adhesion mechanisms and layer uniformity due to micro-load scale contacts and precision sensors. This is important for both quality control and innovation. In addition, the concept of separation energy is introduced to consider both cohesion and adhesion properties and potentially offer an alternative way of examining the behavior of adhesives.

2. Materials and Methods

To establish a method for measuring the adhesion tapes, five commercially available tapes were selected, namely (1) paper masking tape, (2) high-temperature tape, (3) insulation tape, (4) duct tape, (5) box wrapping tape, and (6) double-sided tape (as indicated in Figure 1a). This selection was made to represent a larger spectrum of commercially available tapes, assuming that, due to their different applicability, they will also exhibit different performance in terms of adhesion. The adhesion and separation energy of these tapes were measured with a Falex Tackiness Adhesion Analyser (TAA) tester, Figure 1b. The tapes were fixed with a clamping system to be under tension and with their adhesive layer facing the counter material, Figure 1c. As a counter material, a 3 mm Ø copper ball was used to create a point contact. Copper was chosen because of its inert and easy to clean surface (compared to other metals), and a point contact is chosen because it generates more repeatable results than area contacts [20]. But depending on the application, different contact geometries (e.g., flat-on-flat), counter materials (metallic, ceramic, and polymeric), and temperatures (build up heating system that can reach up to 120 °C) can be used to modify the procedure based on a specific application.

During an indentation–retraction test measurement, the counter material is gradually brought into contact with the adhesive layer of the tape (approach speed 0.01 mm/s), until a preset load of 50 mN. The counter material maintains this load for 10 sec and then gradually moves away from the tape with a well-controlled retraction speed of 0.1 mm/s, until there is complete physical separation. Note that faster separation speeds are also possible but a compromise between speed and measurement resolution will need to be made. Based on the authors’ experience during the development of ASTM D8576 [20], a higher repeatability was observed for retraction speeds in the range of 0.1 mm/s, whereas a load of 50 mN was selected to have a higher surface effect. Throughout the indentation retraction process, the force and counter material displacement are recorded continually, allowing for the creation of indentation–retraction loops. A summary of contact conditions is given in

Table 1. Experimental parameters for indentation-retraction tests with Falex Tackiness Adhesion Analyser (TAA) tester.

Countermaterial:	Cu ball
Counterface diameter:	3 mm
Approach speed:	0.01 mm/s
Applied load:	50 mN
Waiting time at applied load:	10 s
Retraction speed:	0.1 mm/s
Temperature:	20 °C
Relative humidity:	45%

. After each indentation–retraction measurement, the tape was removed, and the counter material was cleaned, until five repeats were performed per tape. The extracted data were analyzed with an Excel macro software and with OriginLab^® OriginPro 9 software.

3. Results and Discussion

Figure 2a presents representative indentation–retraction curves from a triplicate test performed on three different samples of duct tape. These curves exhibit consistent repeatability and follow a similar pattern. The observed pattern consists of two main stages: the indentation stage and the retraction stage. During the indentation stage, the counter material approaches the tape at a slow speed of 0.01 mm/s until it makes physical contact. This contact is indicated in the curve by an increase in the applied load. The load continues to rise until reaching the preset value of 50 mN, which is then held constant for 10 s. Subsequently, the retraction stage begins as the counter material starts moving away from the tape at a fixed speed of 0.1 mm/s. For the retraction to initiate, the maximum adhesive force of the tape must be overcome, as illustrated in Figure 2b. This maximum force is referred to as the pull-off force, consistent with the ASTM D 8576-24 definition. Once this pull-off force is reached, the counter material begins to detach from the tape but maintains some contact with the tape, gradually shearing it. This is indicated by a non-zero force on the sensor, showing that during a retraction of the sensor of about 0.5 mm, there is still some adhesive bonding, smaller than the maximum force. When the counter material completely breaks free from the tape, no force is recorded anymore. Depending on the strength and characteristics of the adhesive layer of the tape, vibrations of the force sensor may occur during the final stage of the separation stage (as shown in Figure 2b). These vibrations result from the sudden separation between the counter material and the tape.

During the whole separation process, displacement until separation occurs because of deformation and shearing of the tape’s adhesive layer, which is viscoelastic and stretches under stress [20]. Also, the backing material of the tape may elastically deform and contribute to this force, and energy is dissipated as the adhesive bond progressively fails [21]. These factors, combined with the contact mechanics which are governed by the interaction of local deformation near contact edges and backing film behavior [22], determine how adhesive materials respond under different conditions. In particular [22], it has been reported that at low velocities, adhesion is enhanced mainly due to increased contact area, while at higher velocities, material stiffness and energy dissipation dominate the process. This balance affects the overall performance of adhesive materials in applications. The integration of separation force over the displacement provides an estimation of the energy required to achieve total physical separation between the counter material and the tape (yellow area indicated in Figure 2b). This can be useful, especially when comparing the overall behavior of adhesive viscoelastic materials, as separation energy accounts for not only the initial pull-off event but also the entire detachment process, including energy dissipation due to deformation, cohesion, adhesion, and the stretching and peeling of the tape during removal. To support this statement, indicative indentation–retraction curves for various commercially available tapes are given in Figure 3a–f.

As seen in Figure 3, the pattern of the indentation–retraction curve changes significantly depending on the characteristics of the tape. In particular, the paper masking tape has a much lower pull-off force compared to the other commercial tapes, which also translates to it being less ‘sticky’. This is desirable in this type of tape, which needs to be removed after painting in a clean and easy manner. However, it can withstand some deformation, indicated by the high displacement prior to complete separation. The high-temperature tape has a completely different pattern, as the separation appears to occur immediately after overcoming the maximum adhesive force. The indentation–retraction pattern of the duct tape resembles that of the paper packaging tape; after overcoming the initial high adhesive force, the tape deforms gradually until complete physical separation (force is no longer recorded). Furthermore, in the case of insulation, box wrapping, and double-sided tapes, the pattern was also similar, but interestingly, after the initial high adhesive force, the interaction force gradually increased again during the separation process, and in the case of the insulation and double-sided tapes, this even overcomes the initial pull-off force. This can be due to changes in the ‘actual’ contact surface during the evolution of the test and the debonding mechanism of the adhesive layer [22]. In addition, overall adhesive performance has been linked to several factors such as surface texture [23], adhesive layer thickness [24] and type [25], deformation rate [26], etc. Thus, to fully understand the cause of this behavior, well-designed experiments need to be performed on laboratory-formulated samples with controlled composition and characteristics of the adhesive layer and backing film. The authors hope that this type of research can be performed in the near future, with the support of an adhesives developer/manufacturer, once this new methodology has been introduced and possibly standardized.

One of the main advantages of this method is that it allows for multiple tests and compares the overall performance of adhesive systems, such as tapes, easily. A comparison of the average pull-off force (maximum force required for separation) and separation energy is shown in Figure 4a and 4b, respectively. Indeed, a different behavior can be seen because a higher force is measured for the double-sided and high-temperature tapes, whereas the lowest force is found for the paper packaging tape. However, a high pull-off force (as it is typically measured in adhesion tests) does not necessarily mean high separation strength, as seen in the case of the high-temperature tape where the separation energy appears to be very low due to the immediate separation of the probe (counter material) after overcoming adhesion force. Furthermore, statistical approaches such as analysis of variance (ANOVA) can be applied to evaluate the significance of difference between these materials. An example of Tukey test analysis for the obtained measurements is presented in Figure 4a,b. This approach is used to determine which specific groups in a dataset are significantly different from each other (marked in red color within the figures), considering the spread of experimental values within each group. For the selected results, the pull-off forces between the double-sided and high-temperature tapes are not significantly different, nor those between the box wrapping, insulation, and duct tape. The largest difference in terms of pull-off force was observed between the double-sided and packaging tape. When analyzing the significance of difference in the separation energy, the smallest difference was observed between the insulation and paper packaging tapes, whereas the largest was observed between the double-sided and high-temperature tapes. The root cause of this variability is complex and can be attributed to several factors. Firstly, the method itself has a variability that can reach up to 10–15%, as described in the ‘repeatability and reproducibility’ section of the ASTM D8576 standard. Secondly, this variability can be also linked to the adhesive layers’ heterogeneity. Adhesive layers in commercial tapes are typically not perfectly uniform, leading to variations in adhesive properties across different locations, even on the same tape roll. In addition, since this method uses a localized point contact, which operates under mN range loads, the generated interaction area/volume would be much smaller than conventional tests. Thus, the results would be more affected by variations in the layers’ surface characteristics (e.g., topography, microstructure, absorbed molecules, etc.). To conclude, we believe that the nature of this variability stems from both the method itself and the material/surface characteristics. However, it should be noted that this ranking is based on the selected experimental conditions (contact geometry, counter material, applied load, and retraction speed) and/or environment (20 °C and 45% relative humidity).

An important feature of this method is its ability to perform multiple measurements at various locations on the same sample, enabling an assessment of the adhesive layer’s homogeneity. However, when conducting consecutive tests, measurements should not be repeated at the same location, and the surface of the counter material must be thoroughly cleaned to ensure accurate results. An example of repeat indentation–retraction tests on the same location is shown in Figure 5. These measurements reveal a clear decrease in pull-off force, displacement to separation, and separation energy over repeated cycles. This decline is often attributed to material transfer, such as free polymer chains or residues, between the adhesive and the counter material. Such transfers alter surface properties and diminish adhesion [27]. Factors including the material’s composition, preparation techniques, curing conditions, and cleaning procedures significantly influence the rate and extent of this adhesive degradation [27]. Overall, this behavior underscores the complex and dynamic interactions—such as material transfer and surface modifications—that occur during indentation–retraction measurements.

This method has significant potential for broader applications beyond its original scope, initially developed for measuring the adhesion and tackiness of greases. This technique can be extended to industries and research areas where adhesion and tackiness of viscoelastic fluids are critical. For instance, in the pharmaceutical and biomedical fields, it could be used to evaluate the bio-adhesive properties of gels and creams, while in the adhesives industry, it can help optimize formulations for pressure-sensitive adhesives and sealants, which are widely used in automotive, aerospace, and packaging applications. Additionally, the method could be applied in food science to characterize the adhesion of food gels and pastes onto surfaces during processing, as well as in soft materials research to study the viscoelastic behavior of complex fluids such as hydrogels and polymeric solutions. Future research on the indentation–retraction method could explore how adhesion and separation energy change under different environmental conditions, such as humidity and temperature, utilizing a built-in heating system capable of reaching up to 120 °C. This is particularly relevant given the diverse applications of adhesive films in medical, packaging, aerospace, and food processing industries. Another research direction could involve studying the aging effects of tapes under various storage conditions, as noted in a related comment. Furthermore, the method could support materials research and surface engineering by investigating the correlation between surface texturing and material composition on adhesive properties. By adjusting the system, contact conditions, and environment, the tests can be fine-tuned for specific applications, further expanding the versatility of this approach.

4. Conclusions

The indentation–retraction methodology provides a precise and versatile approach for evaluating the adhesive performance of commercial tapes. By enabling multiple tests across different sample locations, it offers critical insights into adhesive layer homogeneity and performance variability. This method enhances the accuracy of adhesive strength measurements and provides a comprehensive understanding of adhesive layer properties through force-displacement curves and separation energy values. The analysis reveals distinct patterns linked to factors such as viscoelasticity, surface texture, adhesive layer thickness, and deformation behavior. While high pull-off forces are often associated with strong adhesion, separation energy provides a more complete assessment by accounting for energy dissipation, cohesion, and adhesion mechanisms. This is particularly evident in high-temperature tapes, where a high pull-off force does not necessarily indicate strong separation resistance. Repeated testing on the same location highlights dynamic changes in adhesion due to material transfer and surface modifications, underscoring the importance of clean counter materials and controlled test conditions. The use of statistical analyses strengthens result reliability by identifying significant differences between adhesive materials, making this method a valuable tool for research, development, and quality control in tape production.