A Mechanical Testing Method for the Seawater Resistance Performance of the Adhesive of Bamboo Splints and Resin

Abstract

The present invention discloses a mechanical testing method for the seawater resistance performance of a bamboo strip and resin adhesive, comprising the following steps: preparing artificial seawater: mixing and dissolving sea salt and distilled water, and adjusting the pH value; preparing specimens: cutting the samples to be tested, applying resin adhesive to the ends, overlapping, curing, and naturally cooling; seawater immersion: selecting several groups of samples with the same quantity, immersing one group in air for 10 days, and immersing the other groups in artificial seawater for different times, followed by wiping or drying; loading the specimens until fracture; recording the tensile strength F of each sample in each group, calculating the average value Fn of the tensile strengths of all samples in a group, and calculating and determining whether it is qualified. The present invention provides a method that can intuitively and quantitatively measure the seawater resistance mechanical performance by comparing the lowest value among the average values of the tensile strengths of multiple groups of samples immersed in seawater for different times with the tensile strength at normal temperature in air, and has high accuracy and small error.

Description

Technical Field

[0001] The present invention belongs to the technical field of mechanical property detection of bamboo composites, and more specifically, relates to a mechanical detection method for the seawater resistance performance of the bond between bamboo strips and resin. Background Art

[0002] Bamboo materials are renewable green environmental protection materials, and the application of bamboo composites is becoming more and more extensive. In recent years, with the increasing maturity of the technology related to bamboo composite pressure pipes, bamboo composite pressure pipes can generally replace traditional pipes such as PVC pipes, polyethylene pipes, fiberglass pipes, cement pipes, spiral welded pipes, and ductile iron pipes in drainage projects, farmland irrigation, petrochemical anti-corrosion and other occasions, and have good application prospects.

[0003] Before preparing the bamboo composite pressure pipe, it is necessary to detect the seawater resistance performance of the bond between bamboo strips and resin, that is, it is necessary to detect the mechanical properties of the raw materials of the bamboo composite pipe after being soaked in seawater for a period of time, so as to determine whether the raw materials of the bamboo composite pressure pipe meet the long-term performance and actual use requirements of seawater resistance.

[0004] The detection of seawater-resistant mechanical properties is an important index for the performance of bamboo composite pressure pipes, especially for bamboo composite pressure pipes used in drainage projects, petrochemical and other fields involving seawater immersion environments. There are already methods for detecting the seawater resistance performance of materials in the prior art. For example, Patent CN108088785A discloses an evaluation method for the fresh seawater / fresh water immersion performance of an anti-fouling coating system, which tests the initial adhesion of the anti-fouling coating system and gives some performance evaluation methods for the material's resistance to seawater immersion. However, on the one hand, it mostly involves the performance of coatings and does not involve the detection of mechanical properties such as the tensile and compressive properties of materials; on the other hand, the bamboo composite pressure pipe is made of bamboo materials as the matrix material and thermosetting resin as the adhesive, and is manufactured by a winding process. Different bamboo winding processes (the thickness and size of bamboo strips, the bamboo winding direction) result in different performances of the manufactured bamboo winding composite pipes. In the prior art, there is not only no method for the mechanical detection of the seawater resistance of bamboo composites, but also due to the particularity of bamboo composites, the existing experimental methods for seawater resistance performance cannot be simply applied to bamboo composites. Summary of the Invention

[0005] In view of the above deficiencies or improvement requirements of the prior art, the present invention provides a method for mechanically testing the seawater resistance of bamboo strips and resin adhesives. By taking the tensile strength of samples soaked in air at room temperature and appropriate humidity for ten days as a reference, a calculation formula for evaluating the seawater mechanical properties of bamboo strips and resin adhesives is given by comparing the tensile strengths in seawater and air. This calculation method is simple and can reasonably reflect the seawater mechanical properties. In addition, when obtaining the tensile strength data of seawater immersion, the tensile strength of samples with several different immersion times is tested, and the minimum value is taken, which also avoids the interference of the immersion time factor and directly reflects the seawater resistance of bamboo composites. This test method is simple, real and highly accurate.

[0006] To achieve the above object, the present invention provides a method for mechanically testing the seawater resistance of bamboo strips and resin adhesives, including the following steps:

[0007] S1 Prepare artificial seawater: Mix sea salt and distilled water evenly and stir until completely dissolved, add NaOH solution to adjust the pH value of the sea salt and distilled water mixture solution to 8.3 - 8.5;

[0008] S2 Prepare specimens: Cut several samples to be tested with a length of L, evenly apply resin adhesive at a distance of H from the end, and overlap with another bamboo strip. Through the overlap, an upper strip, a lower strip and an overlapping part are formed. Put the overlapped samples into an oven and cure for at least two hours, and then take them out and cool naturally;

[0009] S3 Seawater immersion: Select several groups of samples to be tested with the same quantity. Put one group into air at 20 - 25 °C and a humidity of 50% - 70% and soak for 10 days, and put the other groups into the artificial seawater respectively and soak for different times for each group; Wipe or dry the soaked samples;

[0010] S4 With the overlap as the center, clamp the two ends of the soaked samples through clamps and install them on a tensile testing machine. After installation and fixation, uniformly and continuously load the specimen until the overlap of the soaked sample breaks;

[0011] Record the tensile strength F of each sample in each group of samples, and calculate the average value of the tensile strengths of all samples in a group as Fn,

[0012] Calculate Draw a conclusion on whether the sample is qualified. Among them, when △ < 15%, the seawater resistance of the tested bamboo composite is qualified;

[0013] In the formula:

[0014] △ ---- Seawater mechanical property index;

[0015] F 1-----The average tensile strength measured for the samples soaked in air at 20 - 25°C and a humidity of 50% - 70% for 10 days;

[0016] Fm ---- The minimum value among the average tensile strengths of the samples soaked in the artificial seawater for different durations.

[0017] Further, in step S3, four groups of samples to be tested with the same quantity are respectively placed in conditions I, II, III, and IV for soaking treatment. Condition I is to be placed in air at 20 - 25°C and a humidity of 50% - 70% for 10 days, condition II is to be soaked in artificial seawater for 10 days, condition III is to be soaked in artificial seawater for 20 days, and condition IV is to be soaked in artificial seawater for 30 days.

[0018] Further, in step S3, the quantity of each group of samples to be tested is at least 3.

[0019] Further, in step S3, after soaking, the samples are wiped or dried to make the moisture content of the samples reach 10% ± 2%.

[0020] Further, in step S2, the two bamboo strips are lapped end to end such that the lapping center point is located at the center position of the sample to be tested.

[0021] Further, in step S4, after the samples are installed on the fixture, uniform and continuous loading is carried out at a speed of 3 - 7 mm / min.

[0022] Further, in step S1, the mass ratio of the distilled water and the sea salt for mixing and preparation is 100:(3 - 7).

[0023] Further, in step S1, the resin adhesive is one or a mixture of several of urea - formaldehyde resin, silicone adhesive, epoxy adhesive, and polyurethane adhesive.

[0024] Further, the reagent for adjusting the pH value of the artificial seawater is a 0.5 mol / L NaOH solution.

[0025] Generally speaking, compared with the prior art by the above - mentioned technical solution conceived by the present invention, the following beneficial effects can be achieved:

[0026] (1) The mechanical testing method for the seawater resistance of the bamboo strip and resin adhesive of the present invention uses the tensile strength of the sample soaked in the air at room temperature and appropriate humidity for ten days as a reference, and gives a calculation formula for evaluating the seawater mechanical properties of the bamboo strip and resin adhesive by comparing the tensile strengths in seawater and air. This calculation method is simple and can reasonably reflect the seawater mechanical properties. In addition, when obtaining the tensile strength data of the seawater immersion, the tensile strength tests are carried out on samples with several different immersion times, and the minimum value is taken, which also avoids the interference of the immersion time factor and directly reflects the seawater resistance of the bamboo composite material. This testing method is simple, real and highly accurate.

[0027] (2) The mechanical testing method for the seawater resistance of the bamboo strip and resin adhesive of the present invention selects several groups of samples to be tested with the same quantity, and the quantity of each group is at least 3. Several more samples will be set for testing in each group, so as to improve the authenticity and rationality of the test and avoid affecting the experimental results due to individual cases.

[0028] (3) The mechanical testing method for the seawater resistance of the bamboo strip and resin adhesive of the present invention overlaps the two bamboo strips end to end to ensure that the overlapping center point is located at the center of the sample to be tested. The overlapping center point located at the center of the sample to be tested can ensure that the forces on both sides of the overlapping part are evenly distributed during the mechanical property test, thus ensuring the accuracy of the seawater resistance mechanical test of the bamboo composite material.

[0029] (4) The mechanical testing method for the seawater resistance of the bamboo strip and resin adhesive of the present invention selects the ratio of sea salt to distilled water in this scheme as close as possible to the actual situation of the seawater in the application area, so that the environment of the artificial seawater is as close as possible to the actual seawater environment to ensure the authenticity and rationality of the test. Detailed implementation mode

[0030] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] A mechanical testing method for the seawater resistance of the bamboo strip and resin adhesive of the present invention mainly includes the following steps:

[0032] S1 Prepare artificial seawater

[0033] S11 Mix distilled water and sea salt evenly at a mass ratio of 100:(3 - 7), and stir with a glass rod until completely dissolved. Among them, the ratio of sea salt to distilled water is selected as close as possible to the actual situation of the seawater in the application area, so that the environment of the artificial seawater is as close as possible to the actual seawater environment;

[0034] S12 Continuously add NaOH solution to the mixed solution of sea salt and distilled water until the pH value of the solution is adjusted to 8.3 - 8.5; preferably, use 0.5 mol / L NaOH solution to adjust the pH value.

[0035] S2 Prepare specimens

[0036] S21 Cut several samples to be tested with a length of L along the length direction of the bamboo strip. The length L is jointly determined according to the needs of the detection device and the bonding length, etc. At least 8 samples to be tested are cut, preferably 24 or more; preferably, 200 mm ≤ L ≤ 500 mm, and at the same time, the clamping requirements of the fixture should be met, and the test samples of the same batch should maintain the same length.

[0037] S22 Uniformly apply resin adhesive at a distance of H from the end and overlap it with another bamboo strip to form an upper strip, a lower strip and an overlapping part through the overlap; preferably, make the overlapping part located at the center of the structure after overlapping. The position of the overlapping center point at the center of the sample to be tested can ensure that the two sides of the overlapping part are evenly stressed during the mechanical property test, thus ensuring the accuracy of the seawater resistance test of the bamboo composite; preferably, 50 mm ≤ H ≤ 100 mm, and the same batch should maintain the same length.

[0038] Among them, the resin adhesive is one or a mixture of several of epoxy resin, polyurethane resin, urea - formaldehyde resin, preferably urea - formaldehyde resin adhesive;

[0039] S23 Put the overlapped samples into the oven and cure for at least two hours, and then cool naturally after taking them out of the oven; preferably, the temperature of the oven is set at 80℃ - 85℃.

[0040] S3 Seawater immersion

[0041] S31 Select several groups of samples to be tested with the same quantity. The quantity of each group is at least 3. Set several more samples in each group for testing, so as to improve the authenticity and rationality of the test and avoid affecting the experimental results due to individual cases;

[0042] S32 Put several groups of samples to be tested with the same quantity into environments with different immersion conditions for immersion respectively. Preferably, put four of them into conditions Ⅰ, Ⅱ, Ⅲ, Ⅳ for immersion treatment, but not limited to the above four immersion treatments, and other conditions with different immersion durations can also be added;

[0043] Among them, condition Ⅰ is to immerse in the air at 20 - 25℃ with a humidity of 50% - 70% for 10 days;

[0044] Condition Ⅱ is to immerse in artificial seawater for 10 days;

[0045] Condition Ⅲ is to immerse in artificial seawater for 20 days;

[0046] Condition Ⅳ is soaking in artificial seawater for 30 days;

[0047] S33 For the samples after soaking above, make the moisture content of the samples reach 10% ± 2% by wiping or drying.

[0048] S4 Mechanical property test

[0049] S41 With the lap joint as the center, clamp both ends of the soaked sample with fixtures and install it on the tensile testing machine. After installation and fixation, load the specimen uniformly and continuously at a loading speed of 3 - 7 mm / min until the lap joint of the soaked sample breaks;

[0050] S42 Record the tensile strength F of each sample in each group of samples, and calculate the average value of the tensile strengths of all samples in a group as Fn;

[0051] Denote the average value of the tensile strength of a group of samples soaked under Condition Ⅰ as F 1 , the average value of the tensile strength of a group of samples soaked under Condition Ⅱ as F 2 , the average value of the tensile strength of a group of samples soaked under Condition Ⅲ as F 3 , the average value of the tensile strength of a group of samples soaked under Condition Ⅳ as F 4 ;

[0052] S43 Calculate Draw a conclusion on whether the sample is qualified

[0053] Where:

[0054] △ ---- Index of seawater resistance mechanical property; and when △ < 15%, the seawater resistance performance of the tested bamboo composite material is qualified;

[0055] F 1 ---- Average value of tensile strength measured from samples soaked in air at 20 - 25℃ and humidity of 50% - 70% for 10 days;

[0056] Fm ---- The minimum value of F 2 , F 3 , F 4 among them

[0057] Taking the tensile strength of the bamboo composite material after soaking at room temperature in air as a reference, compare the minimum value of the tested tensile strengths after soaking in seawater for 10 days, 20 days, and 30 days with the reference value to reflect the seawater resistance mechanical property of the bamboo composite material. By comparing with the reference, an intuitive data comparison method can be given. At the same time, by taking the minimum value among the test values of samples soaked for different durations, the interference of the soaking duration factor is avoided, and the seawater resistance performance of the bamboo composite material is directly reflected. This test method is simple and has high true accuracy.

[0058] The following are several sets of experimental data obtained by testing according to steps S1 to S4:

[0059] Specific test example 1

[0060]

[0061] Specific test example 2

[0062]

[0063] Specific test example 3

[0064]

[0065] Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A mechanical testing method for the seawater resistance performance of bamboo strips and resin adhesives, characterized in that, it includes the following steps: S1 Prepare artificial seawater: Mix sea salt and distilled water evenly and stir until completely dissolved, add NaOH solution to adjust the pH value of the sea salt and distilled water mixture solution to 8.3 - 8.5; S2 Prepare specimens: Cut several samples to be tested with a length of L, evenly apply resin adhesive at a distance of H from the end, and overlap with another bamboo strip. Through the overlap, an upper strip, a lower strip and an overlapping part are formed. Put the overlapped samples into an oven and cure for at least two hours, then take them out and cool naturally; S3 Seawater immersion: Select several groups of samples to be tested with the same quantity. Put one group into the air at 20 - 25°C and a humidity of 50% - 70% for 10 days, and put the other groups into the artificial seawater for immersion with different immersion times for each group; Wipe or dry the immersed samples; S4 With the overlap as the center, clamp the two ends of the immersed samples with clamps and install them on a tensile testing machine. After installation and fixation, uniformly and continuously load the specimens until the immersed samples break; Record the tensile strength F of each sample in each group of samples, and calculate the average value of the tensile strength of all samples in a group as Fn, Calculation Draw a conclusion on whether the sample is qualified. Among them, when △ < 15%, the seawater resistance performance of the measured bamboo composite material is qualified; where: △ ---- Seawater resistance mechanical property index; F 1 -----Average tensile strength measured on samples immersed in air at 20 - 25°C and a humidity of 50% - 70% for 10 days Fm ---- The minimum value among the average values of the tensile strengths of the samples immersed in the artificial seawater for different durations.

2. A mechanical testing method for the seawater resistance performance of bamboo strips and resin adhesives according to claim 1, characterized in that, in step S3, select four groups of samples to be tested with the same quantity, and put them into conditions Ⅰ, Ⅱ, Ⅲ, and Ⅳ for immersion treatment. Condition Ⅰ is to put them into the air at 20 - 25°C and a humidity of 50% - 70% for 10 days, condition Ⅱ is to immerse them in artificial seawater for 10 days, condition Ⅲ is to immerse them in artificial seawater for 20 days, and condition Ⅳ is to immerse them in artificial seawater for 30 days.

3. A mechanical testing method for the seawater resistance performance of bamboo strips and resin adhesives according to claim 1 or 2, characterized in that, in step S3, the quantity of each group of samples to be tested is at least 3.

4. A mechanical testing method for the seawater resistance performance of bamboo strips and resin adhesives according to claim 1, characterized in that, in step S3, after wiping or drying the immersed samples, the moisture content of the samples should reach 10% ± 2%.

5. A mechanical testing method for the seawater resistance performance of bamboo strips and resin adhesives according to claim 1, characterized in that, in step S2, the overlap is carried out symmetrically so that the overlap center point is located at the center of the sample to be tested.

6. A mechanical testing method for the seawater resistance performance of bamboo strips and resin adhesives according to claim 1, characterized in that, in step S4, after the samples are installed on the clamps, the uniform and continuous loading speed is 3 - 7 mm / min.

7. A mechanical testing method for the seawater resistance performance of bamboo strips and resin adhesives according to claim 1, characterized in that, in step S1, the mass ratio of distilled water to sea salt in the mixed preparation is 100:(3 - 7).

8. A mechanical testing method for the seawater resistance performance of a bamboo strip and resin adhesive, according to claim 1, characterized in that, in step S1, the resin adhesive is one or a mixture of several of urea-formaldehyde resin, silicone adhesive, epoxy adhesive, and polyurethane adhesive.

9. A mechanical testing method for the seawater resistance performance of a bamboo strip and resin adhesive, according to claim 1, characterized in that, the NaOH solution with a pH value of 0.5 mol / L is used to adjust the pH value of the mixed solution.

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