In the experiment of fiber content, the sample preparation of blended samples is needed after the qualitative analysis of fibers, that is, before chemical dissolution quantification; for samples without chemical dissolution, the physical resolution method can quantify. According to GB/T 10629-2009 "Preparation of Laboratory Samples and Samples for Textiles Used in Chemical Tests", when preparing samples, for common samples, in order to make them representative, the weight of a single sample is generally about 1.0g about, the sample requires parallel testing. Textiles are usually divided into knitted fabrics and woven fabrics. Sampling methods for different fabrics are different. Sampling methods for general and special samples are described below.
Sample preparation method for woven fabric samples
Sample preparation methods for woven fabrics are generally divided into two situations: the case of sample disassembly after trimming and the case of sample disassembly after trimming.
1.1 the condition needed to be removed after trimming:
samples containing wool must be broken after the edges.
the fabric is thicker and the reagent is difficult to soak the sample to be dissolved.
split sample: separate the warp and weft yarn after trimming or divide the yarn into several heaps according to the sample cycle.
samples dissolved by zinc chloride formic acid need to be disassembled.
1.2 the condition that the sample should not be broken after trimming.
Samples directly dissolved by sulfuric acid method, such as polyester fibers / & nbsp; cotton or linen, polyester fibers / & nbsp; viscose fibers, polyester fibers / & nbsp; model fibers and Lesser fibers;
Samples directly dissolved by dimethylformamide, such as: viscose / & nbsp; spandex, cotton / & nbsp; spandex, model / & nbsp; spandex, polyester / & nbsp; viscose / & nbsp; spandex, polyester / & nbsp; cotton / & nbsp; spandex and other blended products;
Light and thin samples of polyurethane, nylon and polyurethane blended yarns, such as & nbsp; silk /& nbsp; mulberry silk /& nbsp, are directly used for chemical dissolution without disassembling yarns after trimming.
Sample preparation method for knitted fabric samples
There are two kinds of knitting sample preparation methods: direct cutting two pieces and narrow strip cutting or splitting.
2.1 cut two pieces directly.
Warp knitting and lace samples, such as polyester / & nbsp, spandex, nylon / spandex, polyester / & nbsp, spandex, etc.
light and thin samples such as T , T-shirt, netted spandex, etc., which do not contain wool or silk.
fabric with larger mesh size and smaller compactness.
Two.2 a sample cut or narrowed or separated.
all wool or silk samples, such as wool / , polyester fiber, wool / acrylic fiber, etc.
Samples with thicker yarns (such as yarn and clothing), such as acrylic / & nbsp, cotton, nylon / & nbsp, viscose, etc.
For cotton /& nbsp; spandex, viscose /& nbsp; spandex, Modal /& nbsp; spandex and other samples containing spandex, the priority of separation and quantification can be selected, so that the results are closer to the true value.
Sample preparation method for special samples
In addition to the usual work samples, there are some samples with large circulation or pattern which are difficult to handle when preparing samples. The following will introduce the preparation methods of some special samples encountered in the daily testing work.
(1) There are two methods for processing woolly textile samples with large circulation: the conventional method is to prepare a complete cycle, because the sample is heavy, it needs to be divided into several groups of small samples to dissolve separately; in addition, there is a time-saving reagent-saving method, cutting half or a quarter of the sample to dissolve in a cycle, from the principle. Both the above and the actual verification experiments confirm that the results obtained by this method are not different from those obtained by conventional methods.
(2) Qualitative results should be communicated with relevant personnel when the content of non-circulating samples with different yarn components is different and can not be separated at the same time.
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(3) Knitted fabrics with more texture, such as plain, rib or mesh on one sample, can be randomly tested if the texture difference caused by weaving is qualitative; however, for the lower end of rib, attention must be paid to whether other yarns are woven, if so. Other yarns should be marked with the main body.
(4) samples containing lace are treated in two cases:
When the cycle is small, several cycles can be taken for sample preparation. When the cycle is large, a cycle can be taken and marked. In shearing cycle, attention should be paid to the characteristics of the cycle, for example, the pattern sometimes reverses direction, or a different pattern in the middle.
When the sample is blended lace composite fabric, one layer is lace fabric, the other is knitted fabric or woven fabric, after qualitative analysis, if the lace fabric and the other layer need to dissolve, the lace should be cut out before tearing off, otherwise the shape and structure of the lace fabric will change, so as to affect the cycle. Then, another layer of material is prepared; if more colloidal substances have a significant impact on the results, it is necessary to communicate with the relevant personnel.
(5) When the sample is a general composite fabric, the upper layer is a blended fabric, the middle layer is a colloidal material, and the lower layer is a single component fabric; when the colloidal material in the sample can be removed, it can be removed by chemical reagent; when the content of colloidal material in the sample is relatively small and the chemical reagent can not be removed, it can be dissolved directly, and finally. The content of colloidal substance is added to the residue; when the content of colloidal substance in the sample is relatively large and the chemical reagent can not be removed, it should be communicated with the relevant personnel qualitatively.
(6) samples that need to be processed before:
For samples with bright powder, one piece should be cut first to meet the needs of sample preparation and remove bright powder with acetone.
For the sample with coating, one piece should be cut first to meet the requirement of sample preparation, and the coating should be removed by dichloromethane.
For blended samples with PU and without acrylic or polyurethane fibers, N is used.N- two methyl formamide removes PU/ composite layer fabric for preparation.
For cotton or linen blended with regenerated cellulose fibers, it is necessary to fade with sodium dithionite to ensure the chemical dissolution.
Nbsp; when the sample has seams or decorative sequins, it can be removed manually. If the upper or lower seams are nylon, the seams and sequins can be removed from the sample by hydrochloric acid.
sample preparation techniques
(1) For a sample of only one yarn, the cone can be used to select the yarn, without the need for each yarn to be disassembled and separated;
(2) For recycled samples, as long as the yarn is fully recycled at the beginning and the end, there is no need to invest too much energy in the intermediate process.
(3) When cutting woven fabrics and knitted fabrics, we can observe the yarn direction or pick out a yarn with a cone to avoid wasting time on edges and save fabric at the same time.
Matters needing attention in sample preparation
Sampling preparation is one of the important steps in the process of fiber content testing. There are many details to be concerned about. The following are summarized:
Nbsp: when separating samples, the yarn should be removed by using disassembly cloth, which should be neat and clean, so as to avoid losing yarn and incorporating yarns of other samples.
For general samples, attention should be paid to the weight of parallel samples to avoid excessive sample weight, consuming sample preparation time and dissolving reagents.
the samples to be disassembled must be broken up, such as wool samples, coarse yarns;
The pretreated samples should be marked with gelatinous substance /& nbsp; coating /& nbsp; composite layer or seam /& nbsp; sequins;
Nbsp; for the samples separated by longitude and latitude and those separated by first disassembly and then dissolution, it should be checked once after disassembly to see whether they are disassembled or not.
When the unidirectional component is not clear when the warp and weft samples are separated, the combustion method can be used to determine the unidirectional component and reserve the sample, or the unidirectional component can be determined according to yarn strength, yarn state and static electricity.
for dissolving samples after dissolution, do not lose the yarn.
Nbsp; counting after sample preparation: in order to improve weighing efficiency, special paper bags for sample preparation need to be marked with date and page number;
Nbsp; after sample preparation, the composition of the sample should be confirmed to avoid writing errors or omissions; when splitting the sample into the weighing bottle, it should be checked whether the number of the bottle body and the cap is the same; and whether the count is consistent with the corresponding number and composition of the bottle;
Nbsp; when preparing a sample, if something happens halfway, the sample should be put into a weighing bottle or handed over to another person to avoid the loss of the sample.
