Method for measuring content of bamboo fibers in bamboo fiber reinforced polyethylene composite pipe

Abstract

The invention belongs to the technical field of detection, and particularly relates to a method for measuring the content of plant fibers in a plant fiber reinforced polyolefin composite pipe. The test method comprises the following steps: (1) sample preparation: selecting a uniform and defect-free area in the plant fiber reinforced polyolefin composite pipe; crushing the sample into powder, and drying to constant weight; (2) extracting by using a solvent (benzene, dimethylbenzene, methylbenzene, amyl acetate, trichloroethylene, decalin, paraffin oil and mineral oil) to remove the polyolefin matrix; (3) separating the bamboo fiber by using a density method: mixing the mixture obtained in the step (2) with carbon tetrachloride, chloroform and the like, uniformly stirring, and standing for layering; separating an upper-layer suspension, filtering by a funnel, and drying to constant weight to obtain plant fiber mass; (4) blank test correction: synchronously performing a blank test without a sample, and measuring the mass of filter paper and solvent residues; and calculating the plant fiber content according to a formula.

Description

Technical Field

[0001] The present invention belongs to the technical field of detection, and particularly relates to a method for determining the bamboo fiber content in bamboo fiber-reinforced polyethylene composite pipes. Background Art

[0002] With the global emphasis on sustainable development and environmentally friendly materials, natural fiber-reinforced polymer composites have been widely used in fields such as automobiles, construction, packaging, and pipelines due to their light weight, biodegradability, low cost, and environmental friendliness. As a typical natural fiber, bamboo fiber is regarded as an ideal reinforcing material to replace traditional glass fiber or carbon fiber due to its high strength, high modulus, rapid regeneration, and low carbon emissions. Taking bamboo fiber-reinforced polyethylene composite pipes as an example, they combine the corrosion resistance and easy processability of polyethylene with the mechanical properties of bamboo fiber, becoming a new type of environmentally friendly material in fields such as municipal water supply and drainage, and agricultural irrigation.

[0003] However, the bamboo fiber content, as a core parameter affecting the performance of BF / PE composite pipes, directly determines the mechanical strength, thermal stability, water resistance, and processing performance of the material. For example, too low bamboo fiber content will lead to insufficient strength of the composite material, while too high content may cause problems such as poor interfacial bonding and decreased melt fluidity. Therefore, developing an accurate and efficient method for determining the bamboo fiber content is of great significance for optimizing the material formula, controlling the production process, evaluating the product performance, and promoting industry standardization.

[0004] Currently, there are various methods for determining the fiber content in fiber-reinforced composites at home and abroad. However, due to the particularity of the bamboo fiber-polyethylene system, the existing technologies still face the following challenges: (1) Limitations of traditional methods: The chemical dissolution method separates fibers by selectively dissolving the matrix polymer (polyethylene) with a solvent. It is a common method for glass fiber-reinforced plastics (such as GB / T2577-2005). However, polyethylene has high chemical stability and requires strong acids (such as concentrated sulfuric acid) or high-temperature organic solvents (such as xylene) for dissolution. This process may damage the cellulose structure of bamboo fiber, resulting in a lower measurement result. In addition, solvent recovery is difficult and there are safety hazards. Thermogravimetric analysis (TGA) is based on the difference in the thermal decomposition temperatures of fibers and the matrix, and calculates the fiber content through the weight loss curve. However, the main components of bamboo fiber (cellulose, hemicellulose, lignin) decompose at 200-400°C, and the decomposition temperature of polyethylene partially overlaps with it, making it difficult to distinguish the thermal weight loss stage. It relies on complex data fitting algorithms, and the accuracy is significantly affected by the heating rate and atmosphere.

[0005] (2)Special properties of bamboo fiber: As a natural fiber, the chemical composition and structure of bamboo fiber are significantly affected by the origin, growth cycle, and pretreatment processes (such as alkali treatment and silane coupling). For example, surface-modified bamboo fiber may retain coupling agents or coating layers, interfering with the test results of chemical methods or spectroscopy. In addition, the multi-scale structure of bamboo fiber (from macroscopic bamboo slices to micro-nano cellulose) results in poor dispersion uniformity in composite materials, with large fluctuations in local content, posing higher requirements for sampling representativeness.

[0006] (3)Lack of industry standards: Currently, the testing standards for natural fiber-reinforced composite materials are not yet perfect. International standards (such as ISO18827:2016) mainly target wood-plastic composite materials, and the determination of fiber content is mostly based on the ash method (high-temperature burning of the matrix). However, the ash of bamboo fiber remaining after the complete combustion of polyethylene only accounts for 1-3% of the original mass. Trace amounts of ash are easily affected by experimental conditions (such as burning temperature and time) and the ash compounds of bamboo fiber, with an error of up to ±5% or more, making it difficult to meet the high-precision requirements.

[0007] In recent years, non-destructive testing technologies such as near-infrared spectroscopy and Raman spectroscopy have been attempted for rapid determination of fiber content. However, the characteristic peaks of functional groups of bamboo fiber and polyethylene overlap (such as C-H bonds), requiring the establishment of complex calibration models, and the generalization ability of the models is restricted by changes in raw material batches. In addition, although X-ray tomography can three-dimensionally characterize the fiber distribution, the equipment cost is high and data processing is complex, making it difficult to popularize in industrial sites.

[0008] In summary, to develop a method for determining the fiber content of bamboo fiber-reinforced polyethylene composite pipes, problems such as the environmental harm of chemical reagents, insufficient precision of thermal analysis, large variability of natural fibers, and low detection efficiency need to be solved. Future research directions may include: optimizing the solvent system to achieve efficient dissolution of polyethylene without damaging bamboo fiber; combining TGA with differential scanning calorimetry to improve the resolution of thermal analysis; or establishing a rapid detection model through multi-modal data fusion. Breakthroughs in such technologies will promote the large-scale application of bamboo fiber composite materials in the pipeline industry and contribute to the implementation of "replacing plastics with bamboo". Summary of the Invention

[0009] The object of the present invention is to provide an accurate, environmentally friendly, and repeatable bamboo fiber content determination technology, which is applicable to the optimization of raw material ratios and product quality control of bamboo fiber-reinforced polyethylene composite pipes.

[0010] To achieve the above object, the present invention provides the following technical solutions: A method for determining the bamboo fiber content in a bamboo fiber-reinforced polyethylene composite pipe, comprising the following steps: (1) Specimen preparation: Select defect-free areas in the bamboo fiber-reinforced polyethylene composite pipe, and cut specimens at three different positions with an axial interval of ≥ 30 cm; After embrittling the specimens with liquid nitrogen, crush them to pass through a 40-mesh sieve, and dry them to constant weight at 103 ± 2 °C; (2) Removal of polyethylene matrix by toluene extraction: Weigh 3.000 ± 0.002 g of the dried specimen, wrap it with filter paper and place it in a Soxhlet extractor; Add toluene solvent, control the boiling temperature at 110 - 115 °C, the circulation rate at 4 - 5 times / h, and continuously extract for 48 - 50 h; Take out the extraction residue, dry it at 115 ± 2 °C and weigh it to obtain the mass m of the mixture containing bamboo fibers and inorganic fillers 试样 ; (3) Separation of bamboo fibers by carbon tetrachloride density: Mix the mixture obtained in step (2) with carbon tetrachloride, stir magnetically for 1 - 2 h and then let it stand for stratification for 24 - 26 h; Separate the upper suspension, filter it through a sintered glass funnel and dry it to constant weight to obtain the mass m2 of bamboo fibers; (4) Blank test correction: Conduct a blank test without specimens synchronously, and measure the residual mass m0 of the filter paper and the solvent; Calculate the bamboo fiber content according to the formula: 。

[0011] Further, the toluene described in step (2) is an analytical pure reagent with a water content of ≤ 0.03%, and the toluene dosage is 170 mL, and the liquid level is 20 mm higher than the overflow port of the Soxhlet extractor.

[0012] Further, the density of the carbon tetrachloride described in step (3) is 1.594 g / cm³, the addition amount is 300 mL, the magnetic stirring speed is 300 rpm, and the standing stratification time is 24 h.

[0013] Further, the sintered glass funnel described in step (3) is of G4 grade with a pore size of 5 - 10 μm, and it is rinsed 3 times with carbon tetrachloride after filtration, with a dosage of 50 mL each time.

[0014] Further, the standard for drying to constant weight in step (1) is that the mass difference between two weighings is ≤ 0.2%, and the standard for drying the bamboo fibers to constant weight in step (3) is that the mass difference between two weighings is ≤ 0.1%.

[0015] Further, the volume of the Soxhlet extractor in step (2) is 250 mL, the extraction time is 48 h, and the toluene remains colorless and transparent during the extraction process.

[0016] Further, after standing for stratification in step (3), the density of the lower inorganic filler is ≥ 2.7 g / cm³, and the density of the upper bamboo fibers is 1.2 - 1.4 g / cm³.

[0017] Further, in the blank test, after the blank filter paper bag undergoes the same extraction, drying, and filtration steps, the measurement error of the residual mass m0 ≤ 0.005 g.

[0018] Further, in step (1), before the sample is pulverized, it is embrittled by liquid nitrogen treatment to avoid polyethylene melting and adhesion.

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. The traditional chemical dissolution method requires the use of concentrated sulfuric acid or high-temperature organic solvents, which easily destroys the cellulose skeleton of bamboo fibers, resulting in a low measurement value and producing harmful waste liquid. This method uses toluene (a low-toxicity solvent) to extract polyethylene step by step, and no strong acid is involved throughout the process, avoiding cellulose hydrolysis or oxidative degradation. Experiments show that after the bamboo fibers extracted by toluene are observed by electron microscopy, the surface microfibril structure is complete, and the fiber diameter distribution is consistent with that of the raw material (RSD ≤ 5%), ensuring the accuracy of subsequent density separation. At the same time, the solvent can be distilled and recycled, and the waste liquid treatment cost is reduced by more than 60%, meeting the requirements of green chemistry and circular economy, and is especially suitable for industrial production lines that need to be regularly detected.

[0020] 2. In the traditional thermogravimetric analysis (TGA), due to the overlapping of the thermal decomposition intervals of bamboo fibers and polyethylene, the error is as high as ±5%. This method uses carbon tetrachloride (density 1.594 g / cm³) density gradient separation to achieve physical phase separation by using the density difference between bamboo fibers (1.2 - 1.4 g / cm³) and common inorganic fillers (such as calcium carbonate > 2.7 g / cm³). Experimental verification shows that after standing for 24 h, the stratification efficiency > 99%, the residual rate of inorganic matter precipitation < 0.3%, and the relative standard deviation (RSD) of the final bamboo fiber content determination ≤ 1.5%, which is significantly better than the ash method (±5%) and the spectral method (±3%). In addition, this method corrects the filter paper residue through a blank test to eliminate the interference of solvent impurities and is applicable to complex systems containing various inorganic fillers.

[0021] 3. This method realizes the accurate determination of the fiber content in bamboo fiber-reinforced polyethylene composite pipes through step-by-step solvent dissolution and density difference separation technology, solves problems such as fiber damage, inorganic interference, and operation risk in traditional methods, and provides reliable technical support for the industrial production and quality control of bamboo fiber composite pipes. Specific embodiments

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] Example 1 This embodiment provides a method for determining the bamboo fiber content in bamboo fiber-reinforced polyethylene composite pipes, which includes the following steps: (1) Specimen preparation: Select defect-free areas in the bamboo fiber-reinforced polyethylene composite pipes, and cut specimens at three different positions axially spaced 40 cm apart; After embrittling the specimens with liquid nitrogen, crush them to pass through a 40-mesh sieve, and dry them to constant weight at 103 °C; (2) Removing the polyethylene matrix by toluene extraction: Weigh 3.000 g of the dried specimen, wrap it with double-layer qualitative filter paper, and place it in a Soxhlet extractor; Add toluene solvent, control the boiling temperature at 112 °C, the circulation rate at 5 times / h, and continuously extract for 48 h; Take out the extraction residue, dry it at 115 °C and weigh it to obtain the mass m of the mixture containing bamboo fibers and inorganic fillers 试样 ; (3) Separating bamboo fibers by carbon tetrachloride density: Mix the mixture obtained in step (2) with carbon tetrachloride, stir magnetically for 1 h and then let it stand for 24 h to separate layers; Separate the upper suspension, filter it through a sintered glass funnel and dry it to constant weight to obtain the mass m2 of bamboo fibers; (4) Blank test correction: Simultaneously conduct a blank test without specimens to determine the residual mass m0 of the filter paper and the solvent; Calculate the bamboo fiber content according to the formula: .

[0024] The toluene described in step (2) is an analytical pure reagent with a water content ≤ 0.03%, and the toluene dosage is 170 mL, and the liquid level is 20 mm higher than the overflow port of the Soxhlet extractor.

[0025] The density of the carbon tetrachloride described in step (3) is 1.594 g / cm³, the addition amount is 300 mL, the magnetic stirring speed is 300 rpm, and the standing time for separating layers is 24 h.

[0026] The sintered glass funnel described in step (3) is of G4 grade with a pore size of 6 μm, and after filtration, it is rinsed 3 times with carbon tetrachloride, with a dosage of 50 mL each time.

[0027] The standard for drying to constant weight in step (1) is that the mass difference between two weighings ≤ 0.2%, and the standard for drying the bamboo fibers to constant weight in step (3) is that the mass difference between two weighings ≤ 0.1%.

[0028] The volume of the Soxhlet extractor in step (2) is 250 mL, the extraction time is 48 h, and during the extraction process, the toluene remains colorless and transparent.

[0029] In the said blank test, after the blank filter paper package undergoes the same extraction, drying and filtration steps, the measurement error of the residual mass m0 ≤ 0.005 g.

[0030] In step (1), the sample was embrittled by liquid nitrogen before crushing to avoid melting and adhesion of polyethylene.

[0031] Example 2 This example provides a method for determining the bamboo fiber content in a bamboo fiber reinforced polyethylene composite pipe, which includes the following steps: (1) Sample preparation: Select defect-free areas in the bamboo fiber reinforced polyethylene composite pipe and intercept samples at 3 different positions axially spaced 30 cm apart; After embrittling the sample with liquid nitrogen, crush it to pass through a 40-mesh sieve and dry it to a constant weight at 105 °C; (2) Removing the polyethylene matrix by toluene extraction: Weigh 3.000 g of the dried sample, wrap it with double-layer qualitative filter paper and place it in a Soxhlet extractor; Add toluene solvent, control the boiling temperature at 110 - °C, the circulation rate at 4 times / h, and continuously extract for 48 h; Take out the extraction residue, dry it at 115 °C and weigh it to obtain the mass m of the mixture containing bamboo fibers and inorganic fillers 试样 ; (3) Separating bamboo fibers by carbon tetrachloride density: Mix the mixture obtained in step (2) with carbon tetrachloride, stir magnetically for 1 h and then let it stand for 24 h to separate layers; Separate the upper suspension, filter it through a sintered glass funnel and dry it to a constant weight to obtain the mass m2 of bamboo fibers; (4) Blank test correction: Simultaneously conduct a blank test without a sample to determine the residual mass m0 of the filter paper and the solvent; Calculate the bamboo fiber content according to the formula: .

[0032] The toluene described in step (2) is an analytical reagent with a water content ≤ 0.03%, and the toluene dosage is 170 mL, and the liquid level is 20 mm higher than the overflow port of the Soxhlet extractor.

[0033] The density of the carbon tetrachloride described in step (3) is 1.594 g / cm³, the addition amount is 300 mL, the magnetic stirring speed is 300 rpm, and the standing time for separating layers is 24 h.

[0034] The sintered glass funnel described in step (3) is of G4 grade with a pore size of 5 μm, and it is rinsed 3 times with carbon tetrachloride after filtration, with a dosage of 50 mL each time.

[0035] The standard for drying to a constant weight in step (1) is that the mass difference between two weighings ≤ 0.2%, and the standard for drying the bamboo fibers to a constant weight in step (3) is that the mass difference between two weighings ≤ 0.1%.

[0036] The volume of the Soxhlet extractor in step (2) is 250 mL, the extraction time is 48 h, and the toluene remains colorless and transparent during the extraction process.

[0037] In the blank test, after the blank filter paper package undergoes the same extraction, drying, and filtration steps, the measurement error of the residual mass m0 is ≤ 0.005 g.

[0038] In step (1), before crushing the sample, liquid nitrogen embrittlement treatment is adopted to avoid the melting and adhesion of polyethylene.

[0039] Example 3 This example provides a method for determining the bamboo fiber content in a bamboo fiber-reinforced polyethylene composite pipe, including the following steps: (1) Sample preparation: Select defect-free areas in the bamboo fiber-reinforced polyethylene composite pipe, and intercept samples at three different positions axially spaced 50 cm apart; after embrittling the samples with liquid nitrogen, crush them to pass through a 40-mesh sieve, and dry them to a constant weight at 103 ± 2 °C; (2) Removing the polyethylene matrix by toluene extraction: Weigh 3.000 g of the dried sample, wrap it with a double-layer qualitative filter paper, and place it in a Soxhlet extractor; add toluene solvent, control the boiling temperature at 115 °C, the circulation rate at 4 - 5 times / h, and continuously extract for 48 h; take out the extraction residue, dry it at 115 °C, and weigh it to obtain the mass m of the mixture containing bamboo fibers and inorganic fillers 试样 ; (3) Separating bamboo fibers by carbon tetrachloride density: Mix the mixture obtained in step (2) with carbon tetrachloride, stir magnetically for 1 h, and then let it stand for 24 h to separate into layers; separate the upper suspension, filter it through a sintered glass funnel, and dry it to a constant weight to obtain the mass m2 of bamboo fibers; (4) Blank test correction: Simultaneously conduct a blank test without a sample to measure the residual mass m0 of the filter paper and the solvent; calculate the bamboo fiber content according to the formula: .

[0040] The toluene mentioned in step (2) is an analytical pure reagent with a water content ≤ 0.03%, and the toluene dosage is 170 mL, and the liquid level is 20 mm higher than the overflow port of the Soxhlet extractor.

[0041] The density of the carbon tetrachloride mentioned in step (3) is 1.594 g / cm³, the addition amount is 300 mL, the magnetic stirring speed is 300 rpm, and the standing time for separating into layers is 24 h.

[0042] The sintered glass funnel mentioned in step (3) is of G4 grade with a pore size of 10 μm, and after filtration, it is rinsed 3 times with carbon tetrachloride, with a dosage of 50 mL each time.

[0043] The standard for drying to a constant weight in step (1) is that the difference in mass between two weighings is ≤ 0.2%, and the standard for drying the bamboo fibers to a constant weight in step (3) is that the difference in mass between two weighings is ≤ 0.1%.

[0044] In step (2), the volume of the Soxhlet extractor is 250 mL, the extraction time is 48 h, and toluene remains colorless and transparent during the extraction process.

[0045] In the blank test, after the blank filter paper packet undergoes the same extraction, drying, and filtration steps, the measurement error of the residual mass m0 is ≤ 0.005 g.

[0046] In step (1), before the sample is pulverized, it is embrittled by liquid nitrogen treatment to avoid melting and adhesion of polyethylene.

[0047] Performance test The measurement method of the present invention is compared with the traditional test method, and the results are shown in Table 1.

[0048] Table 1 Performance test results

[0049] From the above performance test results, it can be seen that the method of the present invention significantly improves the accuracy, precision, and anti-interference ability of bamboo fiber content determination through multi-stage separation (dissolution-density gradient) and strict blank correction, and is particularly suitable for complex composite material systems containing inorganic fillers. It has clear practical value in the fields of industrial quality control, material research and development, etc.

[0050] The above is the preferred implementation manner of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for determining the content of plant fibers in a plant fiber reinforced polyolefin composite pipe, characterized in that, It includes the following steps: (1) Specimen preparation: Select a uniform and defect-free area in the plant fiber-reinforced polyolefin composite pipe; crush the specimen into powder and dry it to a constant weight; the crushing method is liquid nitrogen embrittlement and mechanical grinding; (2)Removing the polyethylene matrix with the extraction solvent: Weigh a certain mass of the dried sample to the nearest thousandth, wrap it with filter paper and place it in a Soxhlet extractor; add the extraction solvent, control the boiling temperature at the boiling point of the extraction solvent, and control the circulation rate and continuous extraction time; take out the extraction residue, dry it and weigh it to obtain the mass m of the mixture containing plant fibers and inorganic fillers. 试样 ; The mass of the plant fibers weighed is determined according to the solvent in the Soxhlet extractor; the extraction solvent can be one or more of benzene, xylene, toluene, amyl acetate, trichloroethylene, decalin, paraffin oil, and mineral oil; the circulation rate is 2-3 / h, and the continuous extraction time is 60h, the circulation rate is 4-5 times, and the continuous extraction time is 45-50h; (3) Separating bamboo fibers by density method: Mix the mixture obtained in step (2) with solvents such as carbon tetrachloride and chloroform, stir magnetically until evenly mixed, and then let it stand for stratification; Separate the upper suspension, filter it through a funnel and dry it to a constant weight to obtain the mass m2 of bamboo fibers; (4) Blank test correction: Simultaneously conduct a blank test without a specimen to measure the residual mass m0 of the filter paper and the solvent; calculate the bamboo fiber content according to the formula: 。 2. The method for determining the bamboo fiber content in the plant fiber reinforced polyolefin composite pipe according to claim 1, characterized in that: The extraction solvent described in step (2) is an analytical reagent, and the extraction solvent can be one or more of benzene, xylene, toluene, amyl acetate, trichloroethylene, decalin, paraffin oil, and mineral oil, and the dosage is such that the liquid level is higher than 2 / 3 of the round-bottom flask.

3. The method for determining the plant fiber content in the plant fiber reinforced polyolefin composite pipe according to claim 2, characterized in that: In step (3), due to different densities, the functions of using carbon tetrachloride and chloroform are to stratify inorganic particles and plant fibers, and just stir evenly and let it stand for stratification.

4. The method for determining the plant fiber content in the plant fiber reinforced polyolefin composite pipe according to claim 3, characterized in that: The type of funnel used for filtration in step (3) is not limited, specifically a sintered glass funnel or a separating funnel.

5. The method for determining the plant fiber content in the plant fiber reinforced polyolefin composite pipe according to claim 1, characterized in that: The standard for drying to a constant weight in step (1) is that the mass difference between two weighings ≤ 0.2%, and the standard for drying the plant fibers to a constant weight in step (3) is that the mass difference between two weighings ≤ 0.1%.

6. The method for determining the plant fiber content in the plant fiber reinforced polyolefin composite pipe according to claim 5, characterized in that: The extraction equipment in step (2) can be a Soxhlet extractor or a fiber determinator.

7. The method for determining the plant fiber content in the plant fiber reinforced polyolefin composite pipe according to claim 6, characterized in that: After standing for stratification in step (3), the lower layer is inorganic filler and the upper layer is plant fiber.

8. The method for determining the plant fiber content in the bamboo plant fiber reinforced polyolefin composite pipe according to claim 1, characterized in that: In the blank test, after the blank filter paper package undergoes the same extraction, drying, and filtration steps, the measurement error of the residual mass m0 ≤ 0.005 g.

9. The method for determining the plant fiber content in the plant fiber reinforced polyolefin composite pipe according to claim 1, characterized in that: Before crushing the specimen in step (1), treatments such as liquid nitrogen embrittlement and mechanical grinding are adopted to avoid melting and adhesion of polyethylene.

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