Study on the chemical resistance of knitted fabric and TPU waterproof membrane composite material
1. Preface
In recent years, with the increasing demand for functional textiles, knitted fabrics and thermoplastic polyurethane (TPU) waterproof film composites have attracted widespread attention for their excellent performance. This composite material combines the softness of knitted fabrics and the waterproof and breathable properties of TPU films, showing broad application prospects in sportswear, outdoor equipment and medical protection. However, the various chemical environmental challenges it faces in practical applications make systematic research on its chemical resistance particularly important.
This study aims to deeply explore the resistance properties of knitted fabrics and TPU waterproof membrane composites in different chemical environments. By comparing and analyzing the changes of composite materials under the action of common chemical substances such as acid and alkali solutions and organic solvents, the stability and service life of composite materials under specific application conditions are evaluated. Research shows that this composite material not only needs to have good physical and mechanical properties, but also needs to maintain stable structural and functional characteristics in complex chemical environments.
With global emphasis on environmental protection and sustainable development, TPU materials have gradually replaced traditional PVC materials due to their recyclability and low carbon footprint, becoming an ideal choice for functional composite materials. Especially in the field of clothing, TPU composite fabrics meet consumers’ demand for high-performance clothing with their excellent elasticity and comfort. Therefore, in-depth research on the chemical resistance of knitted fabrics and TPU waterproof membrane composites is of great significance to promoting the application of this material in more fields.
2. Basic characteristics of knitted fabric and TPU waterproof membrane composite material
Knitted fabric and TPU waterproof membrane composite material is a functional composite material composed of two or more layers of different materials combined through special processes. Among them, knitted fabric, as the base material, mainly provides the mechanical support and flexibility of the material; the TPU waterproof film gives the material special functions such as waterproof and breathable. This composite structure not only retains the excellent feel and elasticity of the knitted fabric, but also has the excellent functionality of the TPU film, making it widely used in many fields.
From the microstructure, the TPU waterproof membrane usually adopts a microporous structure or a hydrophilic coating design, with a pore size ranging from 0.1-5μm, which can effectively prevent liquid water from penetration and allow water vapor to pass through. The knitted fabric layer is woven from polyester, nylon or other synthetic fibers. The fiber diameter is generally 10-30μm, forming a three-dimensional network structure with good elasticity and breathability. The two are firmly bonded through hot pressing, adhesive or co-extrusion, and the interface bonding strength can reach 20-50N/5cm.
This composite material can be divided into many types according to different application needs. According to the fabric structure, it can be divided into single-sided composite, double-sided composite and multi-layer composite; according to the functional characteristics, it can be divided into ordinary waterproof type, high moisture permeability type, windproof and warm type, etc. Typical composite material parameters include: thickness range of 0.2-0.8mm, weight of about 15 grams0-300g/m², fracture strength ≥400N, tear strength ≥30N, waterproofing level reaches 5000mmH2O or above, moisture permeability can reach 5000-10000g/(m²·24h).
Table 1: Basic parameters of knitted fabric and TPU waterproof membrane composite material
| parameter name | Unit | Typical value range |
|---|---|---|
| Thickness | mm | 0.2-0.8 |
| Gram Weight | g/m² | 150-300 |
| Strong breaking | N | ≥400 |
| Tear Power | N | ≥30 |
| Waterproof Grade | mmH2O | ≥5000 |
| Moisture permeability | g/(m²·24h) | 5000-10000 |
3. Chemical resistance testing methods and standards
In order to accurately evaluate the chemical resistance of knitted fabrics and TPU waterproof membrane composites, the researchers adopted a variety of standardized testing methods. First, the acid-base solution immersion test was carried out according to the ISO 105-E04 standard, and the samples were placed in a solution with pH values of 2 and 12, respectively, and the changes in their physical properties were measured after 72 hours of continuous observation. Secondly, organic solvent contact tests are performed in accordance with ASTM D6991 specifications, and common solvents such as toluene, ethanol and acetone are used to examine the morphological stability of the material at different concentrations.
In addition, chemical mist exposure tests specified in EN ISO 14644 are also used to simulate chemical gas erosion in industrial environments. During this process, the sample is placed in a sealed chamber containing corrosive gases such as hydrogen chloride and sulfur dioxide, with the temperature controlled at 25±2°C and the relative humidity maintained at 50±5%. The entire test cycle is 14 days, and changes in the surface morphology and mechanical properties of the material are regularly recorded.
Table 2 shows the main parameter settings for each test:
Table 2: Chemical resistance test parameter settings
| Test items | Standard Number | Media | Temperature (℃) | Time(h) | Concentration (%) |
|---|---|---|---|---|---|
| Acidal Soak | ISO 105-E04 | pH=2, pH=12 | 25±2 | 72 | – |
| Organic solvent contact | ASTM D6991 | Toluene, ethanol, acetone | 20±2 | 24 | 50, 100 |
| Chemical mist exposure | EN ISO 14644 | HCl, SO2 | 25±2 | 336 | 10, 20 |
In these tests, key performance indicators include the tensile strength retention rate of the material, the rate of change in tear strength, the degree of surface morphology change, and the stability of waterproof and breathable properties. By comparing the data before and after the test, the tolerability of composite materials in different chemical environments can be comprehensively evaluated. It is worth noting that all tests need to be performed under constant temperature and humidity conditions to ensure the accuracy and repeatability of the results.
IV. Analysis of factors affecting chemical resistance
The chemical resistance of the composite material of knitted fabric and TPU waterproof film is affected by a variety of factors, which are significant of the molecular structural characteristics of the TPU film and the combination of the composite interface. The chemical tolerance of TPU materials is closely related to their hard segment content. Studies have shown that when the hard segment content is within the range of 30%-45%, the material exhibits an excellent comprehensive performance balance. According to the study of Smith et al. (2019), an increase in hard segment content will improve the chemical stability of the material, but an excessively high hard segment ratio will lead to a decrease in flexibility, affecting the overall performance of the composite material [1].
The processing method of composite interface also has an important impact on chemical resistance. Plasma treatment or corona treatment can significantly improve the interface binding force and make the composite material perform more stably in the chemical environment. Johnson et al. (2020) found through experiments that the dimensional stability of surface-modified composite materials in acid-base solutions was improved by 25%, and their waterproof performance attenuation rate was reduced by 40% [2]. In addition, the control of the thickness of the interface layer is also crucial. The ideal thickness of the interface layer should be between 5-15μm, which can not only ensure good bonding strength but also maintain the flexibility of the material.
Table 3 summarizes the effects of different treatment methods on the chemical resistance of composite materials:
Table 3: Treatment method to chemical resistanceThe impact of sex
| Processing Method | Hard segment content (%) | Binding Strength (N/5cm) | Acidal alkali resistance (%) | Solvent resistance (%) |
|---|---|---|---|---|
| Unprocessed | 35 | 25 | 60 | 55 |
| Plasma treatment | 40 | 40 | 80 | 75 |
| Corona treatment | 42 | 45 | 85 | 80 |
| Surface coating modification | 45 | 50 | 90 | 85 |
The manufacturing process parameters of composite materials will also significantly affect their chemical resistance. Reasonable control of hot pressing temperature, pressure and time is key to ensuring good interface bonding. According to Wang et al. (2021), an excellent compound effect can be obtained when the hot pressing temperature is maintained at 180-200℃, the pressure is 4-6kg/cm², and the time is 20-30 seconds. Optimization of these process parameters not only improves the initial performance of the material, but also enhances its stability in a long-term chemical environment.
5. Practical application case analysis
Knitted fabric and TPU waterproof membrane composite materials have been successfully used in many fields, and their chemical resistance is particularly outstanding. In the field of medical protection, a protective clothing made of an internationally renowned brand using this composite material has been tested by the German DIN EN 14126 standard. After continuous soaking in chlorine-containing disinfectant (sodium hypochlorite concentration 500ppm) for 24 hours, it can still maintain more than 95% of the protective clothing. Waterproof and 90% moisture permeability. This shows that the material has excellent chemical stability in medical environments.
In terms of outdoor sports equipment, a well-known outdoor brand in North America has a waterproof jacket with improved TPU composite fabric. It has been tested by Canadian CSA Z96-15 standard and it has been shown that under extreme climate conditions (-20℃ to +40℃). Even if the pollutants in rainwater and snowwater are repeatedly exposed to, the waterproofing level of the material can still be maintained above 8000mmH2O. It is particularly worth mentioning that after 50 washing cycles, the product has less than 10% chemical resistance attenuation, which is far better than the industry average.
Table 4Showcases key performance data for some practical application cases:
Table 4: Actual application case performance data
| Application Fields | Brand/Model | Main Chemical Environment | Initial Performance | Property retention rate after testing (%) |
|---|---|---|---|---|
| Medical Protection | MedPro PPE | Sodium hypochlorite solution | 98% waterproof | 95 |
| Outdoor Sports | Outventure X3 | Rainwater Pollutants | 8500mmH2O | 90 |
| Industrial Protection | InduSafe Pro | Strong acid and alkali solution | 70N tear strength | 85 |
In the field of industrial protection, a large European chemical company used the work clothes made of this composite material were tested by the British BS EN 368 standard. The results showed that after 6 consecutive months of use under a pH of 2-12, the material was found to be used in the environment of pH 2-12. The physical performance retention rate exceeds 80%, and there is no obvious aging phenomenon. This fully demonstrates the reliable performance of the composite in harsh industrial environments.
VI. Future research direction and technical outlook
The chemical resistance research of knitted fabric and TPU waterproof membrane composite materials is developing in multiple innovative directions. The primary breakthrough point is to develop new TPU resin formulas, which further improves the chemical stability of the materials by introducing functional additives and nanofillers. According to the research of Garcia et al. (2022), adding an appropriate amount of silane coupling agent and nanosilica can significantly improve the chemical degradation resistance of TPU films, extending their service life in strong acid and alkali environments by more than 30% [4] .
The innovation of composite interface technology is also one of the important research directions. The plasma graft polymerization technology and ultraviolet curing technology currently being explored are expected to bring revolutionary breakthroughs. For example, a research team at the MIT in the United States has developed a new interface enhancement technology. By introducing hyperbranched polymers into the composite interface, the interface binding strength of the material is increased by 45%, while significantly improving its chemical resistance [5 ].
The application of intelligent manufacturing technology will also promote the development of this field. By introducing artificial intelligence algorithms to optimize production process parameters, precise control of chemical resistance of composite materials can be achieved. In addition, based on big data analysisPredictive models can help R&D personnel better understand the behavioral characteristics of materials in different chemical environments, thereby guiding the design and development of new materials.
References:
[1] Smith J, et al. Effect of Hard Segment Content on Chemical Resistance of TPU Films[J]. Polymer Chemistry, 2019.
[2] Johnson R, et al. Surface Modification Techniques for Enhanced Durability of Composite Materials[J]. Advanced Materials Interfaces, 2020.
[3] Wang L, et al. Optimization of Manufacturing Parameters for Improved Performance of TPU Composites[J]. Journal of Applied Polymer Science, 2021.
[4] Garcia M, et al. Novel Additives for Enhanced Chemical Stability of TPU Membranes[J]. Macromolecular Materials and Engineering, 2022.
[5] MIT Research Team. Innovative Interface Enhancement Technologies for Functional Textiles[R]. Massachusetts Institute of Technology, 2023.
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