Rationale
A tensile stiffness tester is an instrument used to measure a material's ability to resist bending or deformation under force. Its core principle, based on the theory of bending in material mechanics, measures the stiffness value of a tissue paper or wrapper sample under specific conditions by applying a controlled force or displacement. Stiffness is usually defined as the moment of resistance to bending of a material, which is closely related to the elastic modulus, thickness and geometry of the material. For tissue paper and wrapping paper, stiffness directly affects their processing performance, packaging support, and user experience.
During testing, the instrument clamps or supports a rectangular sample on a specific fixture that bends the sample through a drive device while measuring the required force or displacement. According to the standard method, the stiffness value can be calculated using the following formula:
\[ S = \frac{F \cdot L^3}{4 \cdot w \cdot d^3} \]
where S represents the stiffness (in millinewton-meters or similar), F is the applied force, L is the length of the sample span, w is the width of the sample, and d is the bending displacement. This formula is based on the bending model of the simply supported beam and is suitable for the testing of most tissue paper materials.
Stiffness requirements for tissue paper and wrapping paper
The stiffness requirements for tissue paper (such as toilet paper, facial tissue) and wrapping paper (such as gift wrapping paper, paper bag paper) vary depending on the application scenario. Tissue paper needs to balance softness with moderate stiffness to ensure comfort during use and maneuverability during processing; The wrapping paper needs to be of high stiffness to provide sufficient support and pressure resistance to protect the contents. Different industry standards have clear definitions of stiffness metrics, such as tissue paper may focus on the longitudinal to transverse stiffness ratio, while wrapping paper emphasizes stiffness retention in wet environments.
The following table lists the typical range and influencing factors of stiffness of common tissue paper and wrapping paper:
| Paper grades | Typical range of stiffness |
| Toilet paper | Low stiffness with an emphasis on softness |
| Facial tissue | Medium stiffness, taking into account strength |
| Gift wrapping paper | High stiffness, emphasis on decoration and support |
| Paper bag paper | High stiffness, need to withstand heavy pressure |
| Influencing factors | Fiber type, slurry ratio, thickness, humidity |
Application in tissue paper
In tissue paper production, tensile stiffness testers are used for quality control and R&D optimization. By measuring stiffness, manufacturers can adjust the slurry ratio, calendering process, or additive dosage to achieve the desired feel and performance. For example, toilet paper requires low stiffness to maintain softness, and a tester can help monitor process fluctuations to avoid excessive stiffness affecting the user experience; Facial tissues need to be moderately stiff to ensure that they are not easy to break when wiped, and the instrument can evaluate the effect of different layers or embossing designs on stiffness.
During testing, relevant standards (such as ISO 2493 or GB/T 23144) are followed, ambient temperature and humidity are controlled, and the sample size is usually long. The instrument automatically completes the bending test, outputs data such as stiffness value and bending curve to assist in the analysis of material anisotropy. This is particularly important for the longitudinal and transverse stiffness of tissue paper, which optimizes slitting and packaging efficiency.
Application in wrapping paper
The stiffness test of wrappers focuses on evaluating their protective properties and processing suitability. High stiffness packaging paper can resist external force deformation, ensure a crisp packaging shape, and at the same time facilitate automatic packaging equipment handling. The tensile stiffness tester can simulate the bending stress of the wrapping paper in stacking and transportation, and measure its maximum bending moment or stiffness index to provide a basis for material selection.
Application cases include weight resistance testing of paper bags: the load-bearing capacity of different quantitative paper samples can be predicted by measuring their stiffness; Gift wrapping paper needs to be tested for compatibility between stiffness and printing coating to avoid coating reducing material rigidity. In addition, the instrument can be used to evaluate the stiffness performance of eco-friendly packaging paper, such as recycled paper, and optimize sustainable formulations by comparing virgin and recycled fiber materials.
TAPPI T543 or similar standards are often referred to in testing, emphasizing sample pretreatment and statistical significance. The following table compares the key parameters in wrapping paper testing:
| Test parameters | Wrapping paper focus |
| Sample orientation | Difference between longitudinal and transverse stiffness |
| Humidity conditions | The rate of change of stiffness with humidity |
| Bending speed | Simulate the actual machining speed |
| Data output | Stiffness value, bending stiffness, coefficient of variation |
Current tensile stiffness testers face some technical challenges in tissue and wrapper applications, such as testing accuracy on ultra-thin materials such as low-volume tissue paper and the stability of wrapper stiffness measurements in high-humidity environments. Instrument manufacturers are responding by improving sensor sensitivity and integrating environmental simulation cabins. At the same time, automation and intelligence have become a trend, such as combining image analysis technology to monitor bending and deformation in real time; Or through the big data platform, the stiffness data is associated with the production process parameters to achieve predictive quality control.
In the future, as the industry's demand for sustainable materials grows, the tester will be more widely used to evaluate the stiffness characteristics of bio-based coatings or composites, promoting the development of tissue paper and packaging paper in the direction of high performance and environmental protection. Standardization efforts are also being updated to accommodate new material testing needs, ensuring data comparability and efficient industry collaboration.
Cited Literature
ISO 2493: Determination of paper and cardboard stiffness
GB/T 23144: Determination of stiffness of paper and cardboard (constant speed bending method)
TAPPI T543: Cardboard stiffness test method
A review of the related stiffness research of "Papermaking Science and Technology"