| Hemp fiber as a kind of green natural textile raw material, people pay more and more attentions on it. Because hemp fibers have several desirable properties, and it accords with the request of the environmental protect and the principle of national textile industry. The relation between the structure and properties is the basic content of macromolecule physics, the structure of fibers is the inner factor of the properties, the properties are the macroscopical exhibition of the structure of fibers, and the properties of fiber affect the craft and quality of yarns directly.The structure of hemp fiber determined its well hygroscopicity, at present, the research of morphology and structure was not enough; the hygroscopicity of hemp fiber and the change of properties before and after moisture absorption had not been analyzed systemically; the effect of moisture regain on the quality of 100% hemp yarns and blended yarns with cotton was still ambiguity.Based on the above questions, this paper developed a series of research work, it expect to supply theoretical guidance to the development and application of hemp fiber. The main woke of this paper were:(1) This paper introduced the phylogeny, classify and the characteristic of hemp fibers, expounded from the history, prevalence, shrink and freshman. Aimed at the research of hemp fibers in recent years, this paper introduced the research actuality of hemp fibers, consulted and put the correlation literature in order. The literatures concluded the structure, morphology, hygroscopicity, spinning technology and the model of materials.(2) This paper tested the chemical composition and constituents, and analyzed the main factors that affect the chemical constituents from degree of processing, different parts, plant condition. It tested the crystal structure by FTIR, X-Ray and X-SAS. Based on the analysis of molecule structure and crystal structure, speculated the combination between cellulose, lignin, hydroxybenzene and miro-tantalum. Finally, it protracted the sketch map of structure model of hemp fiber. It analyzed the morphology character by optical microscope, SEM and TEM. (3) This paper expounded the moisture absorption mechanism and theory textile fibers from the effect of hydrophile group, crystallinity, specific surface area, inner hole, concomitant, impurity and environment on hygroscopicity. It analyzed lag of moisture absorption, the moisture absorption and desorption curve under different regain, wicking property, and the effect of humidity on combing length and fineness of hemp fibers.(4) Focused on the characteristic of quick moisture absorption and desorption of hemp fibers, combined the analysis of EMC of materials inside and outside our nation, this paper selected 5 most commonly used models, non-linear regression was used to fit the models. At last, it compared the goodness of fit of five models, optimized the parameters of the best model, and determined the best parameter for different fineness hemp fibers.(5) This paper tested the tensile performance, surface friction performance and electric performance before and after moisture absorption, and according to Euler load principle, it tested equivalent bending mould and rigidity by single-fiber axial compression bending method, at last, it analyzed the flexibility of hemp fibers.(6) Based on the analysis of effect of humidity on performance of hemp fibers, this paper selected two craft to spinning that is 100% hemp yarns and blended yarns with cotton. It discussed the effect of humidity act on part of spinning machine on the quality of hemp yarns. Arranged the order of the two spinning craft under the change of moisture regain by gray near-optimality.By the research of this paper, the conclusions were as follows:(1) The growing, processing and application of hemp have a very long history; people accumulated a great deal of experience, literature and data about hemp fibers. However, the government banned to grow hemp in recent a century, so the structure and performance of hemp fiber lack of research and analysis. At the same time, the moisture plays a important function on the quality of fibers and spinning, and the literature reports about this aspect are not enough. Therefore, this paper has a definite novelty on the research of structure, morphology, hygroscopicity and the quality of yarns, and it can supply theoretical reference to science and technology operator engaged in hemp research domain.(2) The lignin in hemp fiber can felt the cellulose by means of physics and chemic. It can make the short hemp fiber with fiber bundle indwell in hemp bast fiber, increased the length of fiber bundle. The hemp fiber had a high crystallinity, a relative small amorphism area, and the integrality of crystal was better, molecule chain arranged orderliness, which just about the fundamental reason of high breaking strength, low elongation, big modulus of hemp fiber. The longitudinal section of hemp fiber was roughness, and fineness asymmetry, big difference in shape of cross section, had knob, cavum and a great deal of nesting holes inner, its surface covered by a great deal of pectin, and gathered by form of fiber bundles. There were many polarity hydrohile groups in hemp fibers, resulted in a well hygroscopicity. Also, owing to the crack and holes, and the holes were connected with mid-cavity by capillary, all kinds of holes nesting one other, this structure made hemp fiber favorable performance of moisture absorption and transmission.(3) The moisture regain of combing should be well situated, the range 10-14% was better by compared the combing length and fineness, the length and the fineness was more uniform and the handle was puff and soft.(4) The modified Halsey model and modified Chung-Pfost model were considered separately the best for predicting the moisture absorption and desorption of hemp fiber in 1500Nm and 2500Nm. The modified Chung-Pfost model was the best for predicting the moisture absorption of hemp fiber in P3000Nm and the modified Halsey model was the best for predicting the moisture desorption of hemp fiber in P3000Nm. For each fineness hemp fiber, the goodness of fit was better between the theoretical data and the test data.(5) After moisture absorption, breaking strength, elongation at break, friction factor and electric property were all increased by different extent. The bending rigidity was decreased, showed that moisture played a function that improved the flexibility of hemp fiber.(6) Spray on the surface of hemp fiber can improve the quality of hemp yarns. For 100% hemp yarns, the order of moisture regain in hemp strip was 9.5%—11.3%—7.4%—13.5%—5.2%;for blended yarns with cotton, the order of moisture regain in hemp roving was 10.07%—8.53%—6.69%—7.35%—12.42%—5.89%。...
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