A polymer moisture-proof sealing material

Abstract

This invention proposes a polymeric moisture-proof sealing material using bio-based polylactic acid as the matrix. Enhanced performance and self-healing capabilities are achieved by adding organically modified montmorillonite nanoclay and polycaprolactone. A 100-micrometer-thick composite film was prepared using a solution casting method. Excellent comprehensive properties were obtained by precisely controlling the mixing, dispersion, and curing parameters. Results show that the composite material has a water absorption rate of only 4.5% within 168 hours, a water vapor transmission rate of 12.1 g / m² / day, a tensile strength of 58.6 MPa, and the ability to self-heal within 72 hours at 50°C.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, and in particular relates to a polymer moisture-proof sealing material. Background Technology

[0002] The increasing demand for high-performance moisture-proof sealing materials in various fields such as electronics, construction, and packaging has spurred the development of advanced solutions with superior performance and sustainability. This invention introduces a novel composite material based on a bio-based polylactic acid (PLA) matrix, which utilizes organically modified montmorillonite nanoclay (… The composite material was reinforced with 30B and polycaprolactone (PCL) was added as a self-healing agent. It was prepared using a solution casting method, with precise control of mixing, dispersion, and curing parameters to produce a 100-micron thick film for subsequent experiments. The composite film exhibited enhanced water resistance, confirmed by reduced water absorption (4.5% within 168 hours, compared to 7.8% for the base polymer), reduced water vapor transmission (12.1 g / m² / day, compared to 23.5 g / m² / day for the base polymer), and improved hydrophobicity (contact angle of 92.4°, compared to 75.2°). Mechanical property testing showed that the composite material had a tensile strength of 58.6 MPa and an elongation at break of 22.3%, compared to 45.1 MPa and 18.5% for the base material, respectively. Furthermore, the composite material exhibited better thermal stability, with a 5% weight loss temperature of 315°C, compared to 275°C for the base material. The addition of PCL imparts significant self-healing properties, enabling complete repair of cracks within 72 hours at 50°C, demonstrating improved structural integrity and service life. This novel composite material offers a promising alternative for applications requiring superior moisture resistance and long-term reliability, exhibiting significant improvements over conventional materials across a range of performance metrics.

[0003] The demand for high-performance moisture-proof sealing materials is growing rapidly across numerous industrial sectors, driven by the need to ensure the integrity, functionality, and durability of a wide range of products. From precision electronic equipment to robust building components and food packaging, effectively preventing moisture penetration is crucial. In the electronics industry, even minute amounts of moisture can lead to corrosion, short circuits, and ultimately, malfunctions in sensitive electronic devices, severely impacting functionality. In the construction industry, moisture penetration can cause structural damage, promote mold and mildew growth, and lead to significant degradation of building materials, potentially jeopardizing the safety of the building itself. In the packaging industry, moisture absorption can cause food spoilage, promote bacterial growth, and significantly reduce the shelf life of packaged goods. Currently available commercial materials, such as polyethylene (PE) and polypropylene (PP), while offering some degree of moisture resistance, often lack the required mechanical strength, barrier properties, and long-term reliability for demanding applications, highlighting the urgent need for more advanced materials.

[0004] These currently commercially available materials, despite their widespread use, have several limitations that restrict their applicability. For example, their insufficient mechanical strength makes them prone to tearing and puncture. Furthermore, their relatively low barrier properties allow moisture to diffuse at unacceptable rates, and their non-biodegradability contributes to significant environmental impacts through plastic waste and pollution. Many products typically require additional coatings and laminations to improve their sealing performance, which significantly increases costs and complicates the manufacturing process. These limitations underscore the critical need for more innovative, robust, and environmentally friendly materials that not only effectively block moisture but also possess good mechanical properties, long-term stability, and sustainability. Summary of the Invention

[0005] A polymeric moisture-proof sealing material is characterized by comprising the following components by weight percentage: 80% bio-based polylactic acid (PLA, density 1.24 g / cm³, glass transition temperature 55-60°C, average molecular weight approximately 100,000 g / mol, purity >99.5%), used as the main matrix material to provide basic mechanical properties and biodegradability.

[0006] Its characteristic is that the component includes 20% polycaprolactone (PCL, density 1.145 g / cm³, melting point between 58-60°C, average molecular weight 50,000 g / mol, purity >99.0%), which is used as a self-healing component to endow the material with self-healing function.

[0007] Its characteristics also include 1% organic modified montmorillonite nanoclay (Cloisite® 30B, density 2.0 g / cm³, average particle size approximately 2.5-3.5 micrometers, purity >98%, surface modifiers are methyl, oil-based, and bis-2-hydroxyethyl quaternary ammonium salt), which is used as a reinforcing agent to improve the mechanical properties and barrier properties of the material.

[0008] The preparation steps of this material include:

[0009] Step 1, Preparation of the basic polymer solution: Add 8.00±0.01g PLA and 2.00±0.01g PCL to a 100mL borosilicate glass beaker, then add 50.0±0.1mL chromatographic grade chloroform (purity ≥99.8%). Stir at 400rpm for 2 hours at 45±0.1°C using a magnetic stirrer, checking every 10 minutes and breaking up any undissolved particles with a glass rod until the solution becomes completely homogeneous and transparent.

[0010] Step 2, Preparation of nano-clay dispersion: Add 0.10±0.001g of organic modified montmorillonite nano-clay to a 20mL glass bottle, add 10.0±0.1mL of chromatographically pure chloroform, and place the glass bottle in an ultrasonic cleaner with a frequency of 40kHz and a power of 80W for ultrasonic dispersion for 30 minutes. During this period, check the water level every 5 minutes to ensure the ultrasonic effect.

[0011] Step 3, Preparation of composite material solution: Slowly pour the nano-clay dispersion prepared in step 2 into the base polymer solution prepared in step 1, and stir at 600 rpm for 30 minutes using a magnetic stirrer at 40±0.1°C, checking the mixing status every 5 minutes to ensure thorough mixing.

[0012] Step 4, film formation: Using a precision coater (adjustable gap, accuracy ±1μm), the mixed solution is coated at a constant speed of 10cm / s onto a 100×100mm glass plate cleaned with ethanol. The wet film thickness is set to 150±1μm. The gap is measured every 5mm along the entire coating blade, and a total of 20 data points are collected to ensure coating uniformity.

[0013] Step 5, Preliminary drying: Place the coated film in a fume hood, control the airflow speed at 0.5±0.1m / s, and dry at room temperature of 22±1°C for 24 hours to allow the solvent to evaporate slowly and prevent bubble formation.

[0014] Step 6, Vacuum drying: Transfer the preliminarily dried film to a vacuum oven and dry it at 50±0.1°C with a vacuum of -20±0.5kPa for 12 hours to completely remove residual solvent.

[0015] Step 7, Finished Product Processing: Carefully peel the dried film (final thickness approximately 100±1μm) off the glass plate using a stainless steel scraper, place it in a sealed polypropylene storage box, and add 10g of silica gel desiccant to control humidity. Store at 22±1°C for later use.

[0016] The present invention has the following beneficial effects: The polymeric moisture-proof sealing material proposed in this invention significantly improves the overall performance of the material by adding organically modified montmorillonite nanoclay and polycaprolactone to bio-based polylactic acid. The composite material exhibits excellent moisture-proof performance, with a water absorption rate reduced to 4.5% (42% lower than the base material) within 168 hours, a water vapor transmission rate reduced to 12.1 g / m² / day (48% lower), and a contact angle increased to 92.4°. Simultaneously, the tensile strength of the material increases to 58.6 MPa (30% increase), and the elongation at break reaches 22.3% (20% increase), demonstrating good mechanical properties.

[0017] The material also exhibits excellent thermal stability and self-healing capabilities. The 5% weight loss temperature is increased to 315°C (40°C higher than the base material), and it shows better chemical stability in acidic and alkaline environments, with an expansion rate only half that of the base material after immersion for 72 hours. More importantly, the material has the ability to completely self-heal within 72 hours at 50°C. This self-healing property significantly extends the material's service life and improves its reliability and durability in practical applications. Detailed Implementation

[0018] To address the limitations of current materials, this invention proposes a method based on polylactic acid (PLA) and organically modified montmorillonite nanoclay (…). The development of a novel composite moisture-proof sealing material combining polylactic acid (PLA) and the self-healing polymer polycaprolactone (PCL). PLA is a bio-based and biodegradable polymer derived from renewable resources, making it sustainable. 30B is a surface-modified layered silicate nanoclay that acts as a reinforcing agent, improving the material's mechanical properties, thermal stability, and barrier performance. Polycaprolactone is a biodegradable and biocompatible polymer that acts as a self-healing agent, enabling the composite material to autonomously repair microcracks and damage. This self-healing property significantly improves the material's overall durability and long-term barrier performance, extending its service life. This carefully combined material provides a unique solution for creating robust, moisture-proof sealing materials with enhanced structural stability and barrier performance. This invention details the preparation process, manufacturing techniques, characterization methods, and comprehensive experimental results of this novel material, demonstrating the improvements achieved by combining these three materials.

[0019] The present invention uses the following materials:

[0020] Polylactic acid (PLA): 4043D, manufactured by NatureWorks LLC, USA. This PLA is a particulate bio-based polymer with a density of 1.24 g / cm³, a glass transition temperature of 55-60°C, and an average molecular weight of approximately 100,000 g / mol (according to supplier data). Purity >99.5%, confirmed by an analytical certificate provided by the supplier. Granules are packaged in 25 kg polyethylene bags, catalog number 4043D-B-001.

[0021] Organic modified montmorillonite nano clay ( 30B): Supplied by BYK Additives & Instruments, Germany. This nanoclay is a powdered, organically modified layered silicate with a density of 2.0 g / cm³ and an average particle size of approximately 2.5-3.5 micrometers. The surface modifier is a methyl, oil-based, bis-2-hydroxyethyl quaternary ammonium salt, which improves its compatibility with the polymer matrix. Purity >98%, confirmed by the supplier. Supplied in a moisture-proof 5kg plastic container, catalog number 1468953.

[0022] Polycaprolactone (PCL): 6500, supplied by Perstorp, Sweden. This PCL is a biodegradable polymer with a density of 1.145 g / cm³, a melting point between 58-60°C, and an average molecular weight of 50,000 g / mol according to the manufacturer. Purity >99.0%. Supplied in 20kg polypropylene bags. Catalogue number: 10165847.

[0023] Chloroform: ACS grade, purchased from Sigma-Aldrich, USA. Chloroform is a liquid with a purity ≥99.8% at room temperature, a density of 1.48 g / cm³, catalog number C2432-1L. The solution is contained in a 1-liter amber glass bottle.

[0024] Deionized water: Prepared using a laboratory Milli-Q water purification system (MilliporeSigma, model Direct-Q3UV), with a resistivity of 18.2 MΩ·cm. Store in a clean polypropylene container until use.

[0025] Hydrochloric acid (HCl): 37% solution, purchased from Sigma-Aldrich, USA. Supplied in liquid form, catalog number 320331-1L, in 1-liter plastic bottles.

[0026] Sodium hydroxide (NaOH): Granular, purchased from Sigma-Aldrich, USA. White granules, purity >98%, catalog number 221465-1KG.

[0027] All materials were used in their condition upon receipt, without further purification, and were stored in a temperature and humidity controlled environment (22°C and 50% relative humidity).

[0028] The basic polymer matrix was synthesized using a two-step solution method to produce a well-mixed PLA / PCL mixture. The mixture consisted of 80 wt% PLA and 20 wt% PCL. The specific method is as follows:

[0029] Solution preparation: In a 100 mL borosilicate glass beaker (Pyrex, model 1000), add 8.00±0.01 g of PLA particles and 2.00±0.01 g of PCL particles. Then, add 50.0±0.1 mL of chloroform (ACS grade, Sigma-Aldrich, C2432-1L). Place the beaker on a magnetic stirrer (IKA C-Mag HS 7, equipped with an IKA 25 mm magnetic stir bar). Stir the mixture at 400 rpm, precisely controlling the temperature at 45±0.1°C for 2 hours, ensuring the stir bar is completely submerged in the mixture. Monitor the temperature using a digital thermometer (Traceable thermometer, Fisher Scientific, model 15-077-21).

[0030] Dissolution and Solution Handling: During these 2 hours, monitor the mixture every 10 minutes, breaking up any undissolved particles with a glass rod to accelerate the dissolution process. After approximately 2 hours, all polymers will be completely dissolved, and the solution will become translucent. Remove the solution from the heat source and cool it at room temperature for 1 hour in a fume hood. Then use the solution for the next step. If not used immediately, seal the solution with sealing film (Parafilm M, Bemis), store it in a sealed glass container (Pyrex, model 7200), and keep it in a fume hood at 22°C.

[0031] The composite material was prepared using a basic polymer matrix and 1 wt% nano-clay. The specific preparation method is as follows:

[0032] Nanoclay dispersion: 0.10±0.001g of organically modified montmorillonite nanoclay ( Place 30B (BYK Additives & Instruments) into a 20mL glass bottle (VWR, #16000-160). Then, add 10.0±0.1mL of chloroform to the bottle. Place the bottle in an ultrasonic bath (Branson 1800, frequency 40kHz, input power 80W, internal volume 2.8L) for 30 minutes to ensure good dispersion. During the ultrasonic process, place the bottle in the center of the ultrasonic bath and check the water level every 5 minutes to ensure stable ultrasonic energy. The bottle should be completely submerged in the ultrasonic bath during the ultrasonic process.

[0033] Mixing of polymer and nanoclay: After sonication for 30 minutes, the dispersed nanoclay solution was added to the previously prepared PLA / PCL solution. The mixture was placed on a magnetic stirrer (IKA C-Mag HS 7) and stirred at 600 rpm using a 25 mm stir bar at a temperature of 40 ± 0.1°C for 30 minutes. The solution was checked every 5 minutes to ensure good dispersion of the nanoclay and thorough mixing of all solutions. The temperature was monitored using a digital thermometer (Traceable thermometer, Fisher Scientific, 15-077-21).

[0034] Thin film preparation: The composite solution was coated onto a horizontal, clean glass plate at a constant speed of 10 cm / s using a BYK coating blade (adjustable gap, model 5102). The glass plate (VWR, 100 x 100 mm, 1 mm thickness, model 16000-020) was cleaned with ethanol and Kimtech wipes before use. The wet film thickness was set to 150 μm using a precision micrometer, and 20 data points were collected every 5 mm along the entire coating blade to ensure a consistent wet film thickness.

[0035] Drying and Curing: After coating, the wet film was dried in a fume hood for 24 hours at an airflow rate of 0.5 m / s, monitored using an impeller anemometer (Extech AN340). The film was then further dried in a vacuum oven (Binder, model VD53, with digital temperature display) at a temperature of 50 ± 0.1°C under a vacuum of -20 kPa for 12 hours. All parameters were calibrated before use to minimize errors. After the drying process, the final film thickness was approximately 100 μm (measured using a Mitutoyo digital micrometer, 293-240-30, resolution 1 μm), and the overall film quality was consistent.

[0036] Film Removal and Storage: Carefully peel the film off the glass plate using a stainless steel scraper (Fisher Scientific, 08-764-1), then store it in a sealed polypropylene box (VWR, 150mm x 150mm x 20mm, model 16000-102) with a 10g silica desiccant packet (Dry & Dry, average moisture absorption 10%, #DD-S10) for humidity control. Store the box in a room at 22°C until use.

[0037] The prepared thin films were processed into different shapes for different experiments:

[0038] Water absorption test samples: The composite film was cut into squares of 20.00±0.05mm x 20.00±0.05mm using a CO2 laser cutter (Epilog Zing 24, output power 30W, laser speed 10mm / s, laser frequency 500Hz, calibrated and error analyzed before use). The initial mass of each sample was between 0.09-0.11g.

[0039] Water vapor transmission rate (WVTR) test samples: Circular samples with a diameter of 50.00±0.05mm were cut using a circular precision die cutter (Atlas, model 2001). The die was cleaned and aligned before each use to ensure accurate cutting and minimize dimensional changes.

[0040] Contact angle measurement samples: Samples measuring 30.00±0.05mm x 30.00±0.05mm were prepared using a CO2 laser cutter (Epilog Zing 24) with the same parameters as above. The samples were inspected using a 10x magnifying optical microscope (AmScope, model IN480T) to ensure there were no burrs.

[0041] Mechanical performance test samples: Dumbbell-shaped samples were cut according to ASTM D638 standard using a precision die-cutting machine (Atlas, model 2002). The gauge length was 20.00±0.05mm and the width was 5.00±0.05mm.

[0042] Thermal analysis of samples: A small piece of approximately 5.0 ± 0.1 mg was cut using ceramic tweezers (VWR, 89031-320) for TGA. The sample mass was measured using an analytical balance (Mettler Toledo, XPE205) before being placed into the TGA.

[0043] Chemically resistant samples: Samples measuring 10.00±0.05mm x 10.00±0.05mm were prepared using a laser cutter (Epilog Zing 24).

[0044] Self-healing test samples: Samples were cut to dimensions of 30.00±0.05mm x 30.00±0.05mm using a CO2 laser cutter (Epilog Zing 24). The correct dimensions of all cut samples were checked and measured using digital calipers (Mitutoyo, model 500-196-30).

[0045] All prepared samples were placed in a humidity-controlled polypropylene box (VWR, equipped with silica desiccant) at 22°C before the experiment.

[0046] The experimental methods follow the specific standards and procedures outlined below:

[0047] Water absorption test:

[0048] Analyze the balance using Mettler Toledo.

[0049] The sample was then completely immersed in 50 mL of deionized water in a 100 mL glass beaker (Pyrex, 1000) at room temperature (22.0 ± 0.1 °C).

[0050] Every 24 hours, the sample was removed from the beaker using tweezers, quickly dried with Kimtech Science Precision Task Wipe Paper (Kimberly-Clark, 34155), and reweighed to obtain the wet weight (Ww). Each side was gently wiped three times with equal pressure, and then weighed immediately. All weights were recorded, and this process continued for 7 days.

[0051] Calculate the water absorption rate (%) using the formula: Absorption rate (%) = ((Ww - Wd) / Wd) × 100. Measure 5 samples at each time point and report the standard deviation and standard error.

[0052] The water absorption rate measured at different time intervals is shown in the table below:

[0053] ;

[0054] Experimental data show that the composite material has significantly reduced water absorption. During the 168-hour test, the average water absorption rate of the base PLA / PCL material was 7.8 ± 0.16%, while the composite material with added nanoclay had an average water absorption rate of only 4.5 ± 0.17%, a reduction of approximately 42%. From the perspective of water absorption kinetics, both materials showed a faster water absorption rate in the first 48 hours, which then leveled off, indicating that the materials gradually reached water saturation.

[0055] Water vapor transmission rate (WVTR) test:

[0056] Water vapor transmission rate was measured according to ASTM E96 standard.

[0057] The test was conducted using a Permatran-W (Mocon Inc., Model 3 / 33) water vapor transmission rate analyzer. The instrument was calibrated prior to testing using a calibration membrane, in accordance with the supplier's agreement. A controlled humidity environment was maintained, and temperature fluctuations were kept within 0.1°C during the test using a Peltier control unit.

[0058] The sample is mounted on the WVTR test plate and secured between the test plates by metal washers.

[0059] The test was conducted at 38.0±0.1°C and 90±0.5% relative humidity. Humidity was controlled by the machine's built-in humidity generator (Mocon, RH control unit). Temperature and humidity were continuously monitored using sensors within the system (Mocon, temperature / humidity sensor). The carrier gas flow rate was 50 ml / min.

[0060] Monitor the weight change of the test tray over 24 hours, collecting readings hourly. Calculate the water vapor transmission rate per square meter (g / m² / day) using the data. Measure three samples and include the standard deviation.

[0061] The detailed hourly weight changes and WVTR are shown in the table below:

[0062] ;

[0063] Under conditions of 38°C and 90% relative humidity, the average water vapor transmission rate of the basic PLA / PCL material was 24.17 ± 0.59 g / m² / day, while that of the composite material decreased to 12.89 ± 0.79 g / m² / day, a reduction of approximately 47%. The measured values ​​of the three parallel samples showed minimal fluctuations (standard errors all less than 1.0 g / m² / day), and the weight changes over 24 hours exhibited a good linear relationship, indicating high reliability of the test results. These data demonstrate that the addition of nanoclay significantly improves the water vapor barrier performance of the material, which is of great significance for moisture-proof performance in practical applications.

[0064] Contact angle measurement:

[0065] The contact angle was measured using a goniometer (Dataphysics Instruments). A 5 μL droplet of deionized water was dispensed from a Hamilton syringe using the OCA15EC automatic dispensing system (accuracy ±0.01 μL, dispensing rate 10 μL / s).

[0066] The contact angle was measured after 5 seconds using integrated software (Dataphysics SCA20), with manual baseline detection. Data was saved to Excel for analysis. All settings were calibrated before testing. Camera settings were calibrated before each use.

[0067] Five measurements were performed at different locations on the sample. The contact angle measurement accuracy was ±0.1 degrees.

[0068] The contact angle measurements of the base polymer and composite materials are shown in the table below:

[0069] ;

[0070] Mechanical testing:

[0071] Tensile tests were performed using a universal testing machine (Instron 3365, 5kN force sensor). The force sensor had a capacity of 5kN and an accuracy within ±0.5%. The machine was calibrated before each use using 1kg, 2kg, and 5kg weights (according to ASTM E4-20 machine verification standard).

[0072] The sample was secured using a pneumatic clamp at a pressure of 500 kPa and a gauge length of 20.00 ± 0.05 mm. The sample was manually aligned using an alignment tool (Instron alignment clamp, ASTM D638), and the alignment was carefully performed manually before applying the tensile load by ensuring that the center of the dumbbell was aligned with the center of the clamp.

[0073] Samples were tested according to ASTM D638 protocol at a beam speed of 5 mm / min, using Bluehill Universal control software (Instron), at 23.0 ± 0.1°C and 50 ± 2% humidity (controlled by the machine-integrated environmental chamber). The gauge length was measured using a precision digital caliper (Mitutoyo, 0.01 mm resolution) before each test.

[0074] Tensile strength (MPa) and elongation at break (%) were calculated using Bluehill software. Five samples were tested in each group, and the standard deviation was also recorded in the final table.

[0075] The tensile strength and elongation at break of all samples are shown below:

[0076] ;

[0077] The data clearly demonstrate that the mechanical properties of the composite material are significantly improved compared to the base PLA / PCL polymer. The base polymer exhibits an average tensile strength of 45.0 MPa, with a standard deviation of 0.33 MPa and a standard error of 0.15 MPa. The elongation at break of the base polymer is 18.5%, with a standard deviation of 0.26 and a standard error of 0.12. In contrast, the composite material demonstrates an average tensile strength of 58.6 MPa, with a standard deviation of 0.45 MPa and a standard error of 0.2 MPa, and an average elongation at break of 22.3%, with a standard deviation of 0.24 and a standard error of 0.10. This means that by adding 1% organically modified nanoclay to the matrix, we achieved a significant increase in tensile strength, increasing it by 13.6 MPa (more than 30% of the base polymer value), while simultaneously increasing the elongation at break by 3.8% (approximately 20% of the base polymer value). The increase in tensile strength and elongation at break confirms that the addition of nanoclay significantly strengthens the polymer matrix. Nanoclays act as load-bearing components in polymers, dispersing stress and increasing resistance to deformation and fracture.

[0078] Thermal stability analysis:

[0079] Thermogravimetric analysis (TGA) was performed using a TA Instruments Q500 with high-resolution TGA capabilities. Calibration was performed before each run using standard calibration materials provided by TA Instruments. A platinum crucible (TA Instruments) was used to hold the sample during the measurement.

[0080] Approximately 5.0 ± 0.1 mg of sample was placed into a platinum crucible using ceramic tweezers. The mass was recorded by the TGA itself, with a measurement accuracy of 0.1 μg. The data acquisition frequency was set to 10 Hz, and the gas flow rate was set to 50 ml / min.

[0081] The sample was heated from 25.0 ± 0.1 °C to 800.0 ± 0.1 °C at a heating rate of 10 °C / min under a nitrogen atmosphere (99.999% purity). All parameters were precisely controlled by software (TA instrument software version 6.0).

[0082] Record the temperature at which the sample loses 5% of its initial mass (T5%), and compare the base polymer and the composite polymer. Test at least three samples and report the mean and standard deviation in the results section.

[0083] The table below shows detailed TGA data for the thermal degradation process, displaying the percentage mass loss of the PLA / PCL base polymer and composite at different temperatures:

[0084] ;

[0085] The results clearly demonstrate that the composite material exhibits enhanced thermal stability. The base polymer had an average T5% of 275°C with a standard deviation of 1.0 and a standard error of 0.58. In contrast, the composite material had an average T5% of 315°C with a standard deviation of 1.0 and a standard error of 0.58. The data clearly show that the addition of nanoclay significantly improved thermal stability (by 40°C). This improvement in thermal stability is likely due to the introduction of the thermally stable nanoclay, which acts as a barrier, reducing the rate of polymer degradation upon heating. This is because the nanoclay slows the diffusion of volatile gases released by the polymer, resulting in a slower thermal decomposition rate in the composite material. This barrier effect, coupled with enhanced structural integrity, gives the composite material higher thermal stability than the base polymer. This improved thermal stability makes the composite material more suitable for use in high-temperature environments.

[0086] Chemical tolerance test:

[0087] Chemical resistance tests were conducted by immersing the samples in 1M hydrochloric acid (HCl) and 1M sodium hydroxide (NaOH) solutions at room temperature (22±0.1°C).

[0088] The 1M HCl solution was prepared by diluting a 37% stock HCl solution with deionized water, and the 1M NaOH solution was prepared by dissolving NaOH granules in deionized water. These solutions were freshly prepared before each test using calibrated measuring instruments. Solutions were prepared in a well-ventilated area while wearing appropriate personal protective equipment.

[0089] Each 10mm x 10mm sample was completely immersed in 20ml of the corresponding solution in a separate 50ml glass beaker (Pyrex, 1000, cleaned and dried with ethanol).

[0090] Visual changes such as color change and expansion were recorded at 24, 48, and 72 hours.

[0091] At each time point, the samples were removed, quickly dried using Kimtech precision wipes (Kimberly-Clark, 34155), and reweighed to determine if there was any weight change. Each sample was measured three times, and its weight was recorded to calculate the mean and standard deviation.

[0092] The visual observations and weight change measurements for the chemical resistance test are shown below.

[0093] ;

[0094] This table describes the visual changes and quantitative changes in weight under acidic and alkaline conditions.

[0095] The table below shows the changes in surface area of ​​the samples after the chemical resistance test:

[0096] ;

[0097] The table above shows qualitative visual data and quantitative weight data. The results clearly demonstrate that the composite material exhibits better chemical resistance in both HCl and NaOH solutions compared to the base PLA / PCL polymer. In HCl solution, the base PLA / PCL polymer showed an increase in swelling from 1.5% to 4.2% after immersion for 72 hours, while the composite material showed an increase in swelling from 0.8% to 2.1%, with the base polymer sample showing significant swelling. The base polymer also showed significant swelling and yellowing in NaOH solution, with the weight increase rising from 2.5% to 8.1%. The composite material showed only a small weight increase from 1.6% to 4.5%. More importantly, partial dissolution of the base polymer was observed after immersion in NaOH solution for 72 hours, while the composite material did not dissolve, and significant dissolution was observed on the material surface during the NaOH test. These observations indicate that the addition of nanoclay improves the chemical resistance of the material in acidic and alkaline solutions, prevents the diffusion of chemicals into the polymer matrix, reduces swelling and yellowing, and prevents dissolution. The nano-clay layer forms a water-impermeable barrier, slowing down the diffusion rate of HCl and NaOH and their subsequent reactions with the polymer matrix.

[0098] Self-healing performance test:

[0099] Micro-scratches were created on the surface of each film using a sharp needle (Hamilton, No. 30). The needle was manually pulled across the surface, with an average force of 0.5 N controlled using a calibrated force gauge (Mark-10, model M5-50). The scratch width was approximately 1 mm and remained consistent across all samples.

[0100] The samples were then placed in a digitally temperature-controlled oven (Fisher Scientific, Isotemp oven, model 650) and incubated at 50.0 ± 0.1°C for up to 72 hours. A high-precision digital thermometer was used to calibrate and monitor the oven during testing. The oven features an air circulation system to ensure uniform temperature.

[0101] The scratch area was measured every 12 hours for a total of 72 hours. The data is shown below:

[0102] ;

[0103] This table quantifies the self-healing properties of composite materials by analyzing changes in scratch area over time. The base polymer showed no signs of healing, with a healing rate of approximately 98%, while the composite material showed significant healing within the first 24 hours and complete healing within 72 hours, with a scratch area of ​​0%. Using the same lighting and camera settings, as well as calibration software, when measuring the area minimized errors in the measurement process.

[0104] This invention details a polymeric moisture-proof sealing material. This composite material is based on a biodegradable polylactic acid (PLA) matrix, reinforced with organically modified montmorillonite nanoclay, and combined with polycaprolactone (PCL) to achieve self-healing capabilities. Detailed characterization was conducted, including water absorption testing, water vapor transmission rate measurement, contact angle measurement, mechanical testing, thermal analysis, chemical resistance testing, and self-healing testing. This comprehensive set of experiments demonstrates that this novel composite material exhibits superior performance compared to the basic PLA / PCL polymer.

[0105] Experimental data show a significant reduction in water absorption and water vapor transmission rate, while the contact angle increases, confirming enhanced hydrophobicity. It also improves mechanical strength, thermal stability, chemical resistance, and self-healing properties. The composite material exhibits a decomposition temperature increase of approximately 40 degrees Celsius with a 5% mass loss, demonstrating significantly enhanced thermal properties. Tensile test data shows that the addition of 1% nano-clay increases tensile strength by over 30%, and the composite material becomes more flexible and durable, with an elongation at break nearly 20% higher than the base material. Microscopic analysis of chemical tests reveals that the composite material exhibits excellent resistance to expansion, degradation, and dissolution under both acidic and alkaline conditions, while the PLA / PCL base polymer material shows obvious signs of damage. Quantitative data analysis using microscopic images demonstrates that the addition of a self-healing agent enables rapid healing within 72 hours. All these enhanced properties make this novel composite material highly competitive in the field of moisture-proof sealing.

Claims

1. A polymeric moisture-proof sealing material, characterized in that, Its components include the following ingredients by weight percentage: 80% bio-based polylactic acid, used as the main matrix material to provide basic mechanical properties and biodegradability; Its characteristic is that the component includes 20% polycaprolactone, which is used as a self-healing component to give the material self-healing function; Its characteristic is that the component includes 1% organically modified montmorillonite nanoclay, which is used as a reinforcing agent to improve the mechanical properties and barrier properties of the material.

2. A polymeric moisture-proof sealing material, characterized in that, The preparation steps of this material include: Step 1, Preparation of the basic polymer solution: Add 8.00±0.01g PLA and 2.00±0.01g PCL to a 100mL borosilicate glass beaker, then add 50.0±0.1mL chromatographic grade chloroform. Stir at 400rpm for 2 hours at 45±0.1°C using a magnetic stirrer, checking every 10 minutes and breaking up any undissolved particles with a glass rod until the solution becomes completely homogeneous and transparent. Step 2, Preparation of nano-clay dispersion: Add 0.10±0.001g of organic modified montmorillonite nano-clay to a 20mL glass bottle, add 10.0±0.1mL of chromatographic grade chloroform, and place the glass bottle in an ultrasonic cleaner with a frequency of 40kHz and a power of 80W for ultrasonic dispersion for 30 minutes. During this period, check the water level every 5 minutes to ensure the ultrasonic effect. Step 3, preparation of composite material solution: Slowly pour the nano-clay dispersion prepared in step 2 into the base polymer solution prepared in step 1, and stir at 600 rpm for 30 minutes at 40±0.1°C using a magnetic stirrer, checking the mixing status every 5 minutes to ensure thorough mixing; Step 4, film formation: Using a precision coater, the mixed solution is coated at a constant speed of 10 cm / s onto a 100×100 mm glass plate cleaned with ethanol. The wet film thickness is set to 150±1 μm. The gap is measured every 5 mm along the entire coating blade, and a total of 20 data points are collected to ensure coating uniformity. Step 5, Preliminary drying: Place the coated film in a fume hood, control the airflow speed at 0.5±0.1m / s, and dry at room temperature of 22±1°C for 24 hours to allow the solvent to evaporate slowly and prevent bubble formation; Step 6, Vacuum drying: Transfer the preliminarily dried film to a vacuum oven, and dry it at 50±0.1°C with a vacuum of -20±0.5kPa for 12 hours to completely remove residual solvent. Step 7, Finished Product Processing: Carefully peel the dried film off the glass plate using a stainless steel scraper, place it in a sealed polypropylene storage box, and add 10g of silica gel desiccant to control humidity. Store at 22±1°C for later use.