Silk Quilt Inspection

Silk quilt inspection mainly conducts scientific testing and analysis on key performance indicators, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Core Testing Items

Fibre composition and content: This item is the core of the silk quilt inspection, aiming to determine the true composition of the filling. The inspection is carried out in accordance with GB/T 24252-2019 "Silk quilts", usually adopting the chemical dissolution method (such as the 75% sulphuric acid method) or the microscope observation method, precisely determining the specific contents of mulberry silk and tussah silk, and identifying whether there is the admixture of other fibres (such as chemical fibres and cotton). It is the basis for judging whether the product is qualified.

Filling mass deviation rate: This item is used to evaluate the conformity between the actual weight of the silk quilt filling and the marked weight. According to the standard provisions, after equilibration under standard atmospheric conditions, the deviation rate between the measured mass and the marked mass should be between -2.0% and +5.0%. An excessively large negative deviation means insufficient filling, which belongs to "short weight", and directly affects the warmth retention and use value of the product.

Oil content: The oil content refers to the content of residual substances such as sericin and wax in the silk, and is an important indicator reflecting the processing technology and purity of the silk. An excessively high oil content (usually the standard requires ≤1.5%) will cause the silk to easily harden and produce odour, and affect its moisture absorption, air permeability and service life. The inspection usually adopts the Soxhlet extraction method, using organic solvents such as ether for extraction and determination.

Moisture regain: The moisture regain indicates the percentage of water contained in the silk. The inspection is carried out under a standard temperature and humidity environment (such as temperature 20±2 ℃ and relative humidity 65±4%). A reasonable moisture regain (usually 8.0%-14.0%) is the basis for the silk to maintain good handle and physical properties. An excessively high moisture regain is prone to mold growth, while an excessively low one causes the fibres to be brittle and hard.

Compression resilience: This indicator comprehensively evaluates the bulkiness, softness and warmth retention durability of the silk quilt. A certain pressure is applied to the filling with a dedicated instrument and maintained for a specified time, and after the pressure is removed, the recovery rate of its thickness is measured. High-quality silk quilts should have good compression resilience, ensuring that they are not easy to harden after long-term use and always remain fluffy and soft.

Fluorescent whitening agents: Tests whether the fabric and filling of the silk quilt contain migratable fluorescent whitening substances. According to the requirements of GB 18401 "National general safety technical code for textile products" and the relevant standards, migratable fluorescent whitening agents must not be detected in textile products in direct contact with the skin, to ensure the health and safety of the users and prevent possible skin irritation or allergic reactions.

Colour fastness: Mainly for the quilt cover fabric of the silk quilt, including the colour fastness to water, perspiration, rubbing and light. The inspection simulates the conditions such as washing, friction and light exposure in daily use, and assesses the fastness of the fabric colour. Poor colour fastness will cause the dyes to fall off and contaminate other clothes or the skin, and is the key to measuring the fabric quality and processing technology.

Testing Scope and Objects

Identification of the silk type of the filling: Clearly distinguishes mulberry silk (domestic silkworm silk) from tussah silk (wild silkworm silk). The two differ significantly in the fibre morphology, length, colour and price. Mulberry silk is white, fine, soft and lustrous; tussah silk is yellowish, with coarser fibres and greater rigidity. The inspection report must clearly indicate the specific type and content percentage, which is the core basis for determining the product grade and price.

Analysis of the quilt cover (case) fabric: The inspection objects include not only the filling, but also the quilt cover wrapping the silk. Its fibre composition (such as pure cotton, polyester-cotton and real silk), fabric weave structure, mass per square metre and safety performance indicators need to be analysed. A high-quality quilt cover should have good air permeability and skin-friendliness, and match the performance of the filling.

Product specification and labelling conformity: In accordance with GB/T 24252 and GB/T 5296.4 "Instructions for use of products of consumer interest — Part 4: Textiles and apparel", it is checked whether the actual specification of the product (size and filling weight) is consistent with the durable label and the marked information on the packaging. At the same time, it is checked whether the labelling contents are complete and standard, including the factory name and address, product name, fibre content, safety category and maintenance methods.

Process structure evaluation: Inspects the quilting process, edge binding process and the fixing method of the internal silk (such as manual positioning, quilting or layered structure) of the silk quilt. It evaluates whether the process can effectively prevent the silk from shifting and clumping during use, affecting the uniformity and comfort of use. This is an important aspect of judging the process quality of the product.

Safety technical category judgement: According to the GB 18401 standard, the silk quilt (mainly referring to the detachable quilt cover) is divided into Class A (infant products), Class B (products in direct contact with the skin) or Class C (products not in direct contact with the skin). Items such as the formaldehyde content, pH value, odour and decomposable carcinogenic aromatic amine dyes need to be tested, ensuring that the product meets the corresponding safety technical requirements.

Appearance quality inspection: Under a standard light source cabinet or north-facing natural light, the overall appearance of the product is inspected. This includes whether the fabric has damage, stains, colour difference and poor printing, whether the sewing stitches are straight, uniform and firm, whether the filling is uniform and flat without obvious hard lumps or impurities, and whether accessories such as zippers are smooth and durable.

Main Testing Methods and Standard Basis

Quantitative chemical analysis of fibre composition (GB/T 2910): This is the method for determining the mixing ratio of silk and other fibres. For different fibre combinations, specific chemical solvents are selected (such as 75% sulphuric acid dissolving silk and retaining cotton; sodium hypochlorite dissolving silk and retaining polyester). Through the steps of dissolution, filtration, drying and weighing, the mass percentage of each component is precisely calculated.

Microscope method (FZ/T 01057): A biological microscope or scanning electron microscope is used to observe the longitudinal and cross-sectional morphological characteristics of the fibres. Mulberry silk has a smooth longitudinal surface and an irregular triangular cross-section; tussah silk has longitudinal stripes and a flat ribbon-shaped cross-section. This method is an intuitive and effective means for identifying the silk type and judging whether other fibres are mixed in.

Oil content determination — Soxhlet extraction method (GB/T 24252): A silk specimen of a known dry weight is wrapped with dedicated filter paper and placed in a Soxhlet extractor. An organic solvent with a low boiling point (such as ether or petroleum ether) is used for continuous circulation extraction, dissolving and removing the oily substances in the fibres. After extraction, it is dried and weighed, and the oil content is calculated through the mass difference.

Moisture regain test — oven method (GB/T 9995): The silk specimen is placed in a constant temperature oven at 105±2 ℃ and dried to constant weight (i.e., the difference between two consecutive weighings does not exceed 0.1%), and the moisture regain is calculated through the mass change before and after drying. The test must be carried out under standard atmospheric conditions for conditioning and weighing, to ensure the accuracy and comparability of the results.

Colour fastness test series (GB/T 3920, 3922, 5713, etc.): Matching dedicated equipment and standard adjacent fabrics are adopted to simulate different conditions for testing. For example, the colour fastness to rubbing uses a rubbing fastness tester, the colour fastness to perspiration uses a perspiration fastness tester with artificial perspiration, and the colour fastness to light uses a xenon arc lamp fading tester. Finally, the fading or staining grades are assessed through the standard grey scales.

Compression resilience test (Annex A of GB/T 24252): A fabric thickness gauge or a dedicated elasticity instrument is used. The silk filling is placed on the test table, a specified pressure (such as 49 kPa) is applied and maintained for a specified time, and the initial thickness, compressed thickness and the thickness after the pressure is removed and recovered for a specified time are measured, calculating the compression rate and recovery rate, to characterize its bulkiness recovery ability.

Testing Instruments and Equipment

Electronic balance: With an accuracy of 0.001 g or higher, it is the basic equipment for almost all quantitative analyses such as the filling mass deviation rate, oil content and moisture regain. It is used for the precise weighing of the samples, and its stability and accuracy are directly related to the reliability of all subsequent calculation results. It must be regularly calibrated.

Fibre fineness analyser and biological microscope: The fibre fineness analyser can automatically measure the fibre diameter and cross-sectional area; the biological microscope (usually equipped with a micro-photography system) is used to observe the longitudinal surface characteristics and cross-sectional morphology of the fibres, and is the core optical instrument for identifying the silk type and judging the fibre quality (such as uniformity and damage).

Soxhlet extraction device: Composed of three parts, the extraction flask, extraction tube and condenser, it uses the solvent reflux and siphon principle to realize the continuous, efficient and thorough extraction of the oily substances in the silk. This device is the dedicated equipment for determining the oil content, and its sealing, condensation efficiency and the purity of the solvent have a major influence on the experimental results.

Constant temperature and humidity chamber and oven: The constant temperature and humidity chamber is used to provide a standard test environment for textile specimens (temperature 20±2 ℃ and relative humidity 65±4%), so that the samples reach the moisture equilibrium, ensuring consistent subsequent test conditions. The forced-air drying oven is used to quickly and uniformly remove the moisture in the samples, to determine the moisture regain or dry weight.

Fabric strength tester and compression elasticity instrument: The fabric strength tester can be used to test the mechanical properties such as the breaking strength and tearing strength of the quilt cover fabric. The compression elasticity instrument is equipped with a pressure plate and sensors that can precisely control the pressure and displacement, and is specially used to measure the thickness, compression and recovery properties of the filling, evaluating its bulkiness durability.

Standard light source colour matching cabinet and colour fastness testers: The standard light source cabinet provides international standard light sources such as D65 and TL84, used to uniformly inspect the appearance colour and colour difference of the product and assess the change in colour/staining grades of the colour fastness, avoiding visual errors caused by different lighting conditions. The colour fastness testers are the general term for a series of dedicated instruments, including simulation test equipment for rubbing, perspiration, washing and sunlight exposure.

Testing Standards

Domestic Standards:

1. GB/T 24252-2019, Silk quilts

2. GB 18401-2010, National general safety technical code for textile products

3. GB/T 2910, Textiles — Quantitative chemical analysis

4. GB/T 9995, Determination of moisture content and moisture regain of textile materials — Oven-drying method

5. FZ/T 01057, Test method for identification of textile fibres

International Standards:

1. ISO 1833, Textiles — Quantitative chemical analysis

2. ISO 105, Textiles — Tests for colour fastness

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.