Study On The Effects Of Pre-wetting On Sized Yarn Properties

The newly developed sizing technique, pre-wet sizing which can not only improve thesizing quality but also helps keep the environment clean, is regarded possibly as the standardsizing process in the future. However, systematic investigations are scantily made on pre-wetsizing. In this thesis, based on the summarization of the recent progress in pre-wet sizing in theworld, corntyaratively systematic study are conducted to investigate the effects of pre-wettingon the size-pick-up and physical mechanical properties of the sized yarn, the size penetrationand encapsulation as well as the warp yarn surface characteristic, etc. The main work in thisthesis includes that both the traditional sizing and pre-wet sizing experiments of 29tex and36.5tex pure cotton yarns using the blended size of mixing oxy-starch with PVA are carded outon the built pilot pre-wet sizing system. The size-pick-up and physical mechanical properties oftotal 40 sized yarn samples are tested according to the designed sizing scheme. Effects ofpre-wetting on size-pick-up and physical mechanical properties of the sized yarn areinvestigated according to the test results. 4 sized yarn samples are cross-sectioned using thenew fiber/yarn microtome developed by ourselves, with which the cross-section thickness canhe controlled precisely. 9 feature indexes are extracted after the digital images of the sized yarncross-section being pretreated. The effects of pre-wetting on the size distribution in the sizedyarn cross-section are further discussed. Based on the developed formulas of the warp yarnsurface flee energy and interface free energy between warp yarn and size liquid, the effect ofpre-wetting on the immersional wetting work, which is yielded when warp yarn beingimmersed in size liquid, are discussed. By measuring the contact angle between warp yarn andsize liquid, the warp yarn capillary effect and adhesive force of size are validated. The maincontents covered in each chapter are as follows.In chapterl after description of the background and significance of the topic selection ofthis thesis, an introduction of the recent progress in many aspects in pre-wet sizing home andabroad is presented, including processing technologies, equipments and the mechanisms of the pre-wetting; the effects of pre-wetting on size-pick-up and physical mechanical properties ofsized yarn, size penetration and encapsulation, and pre-wetting mechanism, etc.In chapter2 the built pilot pre-wet system constructed by ourselves, experimental materialsand process parameters are introduced firstly. In this study 29tex and 36.5tex pure cotton yarnsare used as experimental materials. The mixed size consists of main size component oxy-starchand assistant size component PVA. Finally, 40 experiments on the traditional sizing, double dipdouble squeeze pre-wet sizing, double dip double squeeze pre-wet twi-sizing are carried outaccording to the designed experimental schemes, and correspondingly 40 sized yam samplesare obtained.In chapter3 the size-pick-up and physical mechanical properties, including breakingstrength, breaking elongation, abrasion resistance, hairiness index, of all the sized yarn samplesobtained in chapter two are tested, meanwhile the testing method and devices are alsodescribed. Based on the testing results the effects of pre-wetting on the size-pick-up andphysical mechanical properties of the sized yam are analyzed.In chapter4 the modifications of Hardy's microtome method and our newly developedfiber/yam microtome are introduced firstly. Then, the sized yarn samples are cross-sectionedwith the newly developed microtome and the digital images of sized yarn cross-sections arecaptured. Following that, the digital images are pretreated, including contrast logarithmicenhancement, image binary conversion, image boundary trace, isolated point and fine branchelimination. Finally the excellent binary images are obtained.In chapter5 the new feature indexes system designed by ourselves is introduced firstly.Then, 9 cross-section feature indexes of 4 types of sized yarn samples are extracted from theobtained binary images. Finally, according to the extracted results of the sized yarncross-sections, the effects ofpre-wetting on size distribution in the sized yarn cross-section arediscussed.In chapter6 the indicating warp yam surface flee energy and interface flee energy betweenwarp yam and size liquid are seduced, consequently the effect of pre-wetting on theimmersional wetting work yield when warp yarn being immersed in the size liquid is predicted.By measuring the contact angle between warp yarn and size liquid, the warp yarn capillary effect and the adhesive force of size, the above prediction is validated. Finally, the actionmechanism of the pre-wetting is summarized.In chapter7 a summary is made to describe the main contributions of the present work andthe problems needed to be further studied. The future work is also prospected.