Development And Application Of Waterborne Polyurethane As Anti-pilling Finishing Agent For Cashmere Knitted Fabric

Cashmere has been known as “diamond fiber” or “soft gold”, and cashmere knitted fabric hasthe superb characteristics of being soft, smooth, plump, aristocratic and elegant. However,cashmere knitted fabric tends to easily fuzz and pill due to the scales on the fiber surface and itsflabby structure, thus resulting in negative effects on its appearance and wearability. At present, itis difficult to find, an anti-pilling finishing agent with preferable performance for cashmere knittedfabric. Waterborne polyurethane (WPU) has good potential as an anti-pilling finishing agent forcashmere knitted fabric, but the common problem is that the handle of fabric treated with WPUtends to be stiff. Therefore, the investigation and development of WPU as an appropriateanti-pilling finishing agent for cashmere knitted fabric through the use of a combined finishingprocess are essential. In addition, it is also very important to prevent the worsening of the fabrichandle caused by the anti-pilling finishing; thus, a softener that would provide an ideal soft andfluffy performance is needed and used as a finishing agent in combination with WPU during theanti-pilling finishing of cashmere knitted fabric.In this study, the research work is centered on the investigation and development of WPUcombined with a soft and smoothing agent as an anti-pilling finishing agent for cashmere knittedfabric. Firstly, a series of amino silicone oils with different structures are synthesized and theirproperties are investigated, and then amino silicone softeners which can impart the treated fabricwith soft and fluffy properties are selected. Secondly, anionic and cationic WPU modified with thetailor made amino silicone oil are synthesized, and the resultant organic silicone oil is introducedand grafted onto the chain segments of the WPU. The properties of this resultant WPU emulsion,latex properties of the WPU and finishing properties of the cashmere knitted fabric treated withWPU in terms of anti-pilling, are tested and analyzed. Furthermore, the relationship between thestructure and properties of the WPU is investigated. Finally, the prepared amino silicone oilsoftener and WPU are applied in a trial as a finishing agent for cashmere knitted fabric, and theanti-pilling finishing properties and resistance to washing of the treated fabric are investigated.Specific details on the research and the main conclusions are as follows:1. Preparation of side-chain amino silicone oil (AEAPS) and linear blocking polyethersilicone oil (PBS). A series of AEAPS and PBS with different ammonia values are synthesized byusing octamethylcyclotetrasiloxane (D4), silane coupling agent602, amino-terminated polyetherand epoxide-terminated polyether silicone. As well, the relationship between the structure andperformance of the AEAPS is analyzed. The results show that with an increase in the ammoniavalue, the molecular weight of the AEAPS tends to decrease, while that of the PBS tends to firstincrease, and then decrease. The properties of the cashmere knitted fabric treated with AEAPS andPBS respectively are obviously different; the former has the handle characteristics of being soft,smooth and a slightly greasy feeling, while the handle characteristics of the latter is fluffy, soft andsmooth. Furthermore, the hydrophilicity, water vapor permeability, and antistatic property of thelatter are better than those of the former, and there is less yellowing. Therefore, PBS excelsAEAPS when used as a soft finishing agent of cashmere knitted fabric. 2. Preparation of WPU modified with side chain type of AEAPS as an anti-pilling finishingagent for cashmere. Polypropylene carbonate polyol (PPC), polytetramethylene glycol (PTMG)and poly-1,4-butylene adipate glycol (PBA) are used as the raw materials for the soft segment inthe preparation of the anionic WPU prepolymer, and then the WPU modified by an organicsilicone is synthesized through the introduction of AEAPS into the WPU prepolymer. Thestructure of the anionic WPU modified with AEAPS is characterized by Fourier transform infrared(FT-IR) spectrometry, gel permeation chromatography (GPC), thermogravimetric (TG) analysis,atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and dynamicthermomechanical analysis (DMA). Moreover, the application of anionic WPU as an anti-pillingfinishing agent for cashmere knitted fabric is investigated. The properties of the WPU that usesPPC, PTMG and PBA for the soft segment, respectively, and the properties of the WPU modifiedwith AEAPS are then studied and analyzed.With PPC as its soft segment, the WPU latex has the following properties: greater hardness,poor water and heat resistance, good compatibility of soft and hard segments, and no obviousmicro-phase separation. There are obvious differences among the latex structure and properties ofthe WPU when PPC, PTMG or PBA is used as the soft segment. However, the formation of acrosslinked structure on the WPU after modification with AEAPS results in an obvious increase ofthe molecular weight, and therefore the water and heat resistances of the WPU latex are improveddue to the polysiloxane chains that gather on the surface of the WPU latex. Moreover, thisphenomenon is much more obvious in the WPU with PPC as its soft segment. Therefore, WPUmodified with AEAPS which uses PPC as the soft segment is effective for improving the totalperformance of the WPU latex.The optimum recipe for the synthesis of WPU as an anti-pilling finishing agent for cashmereknitted fabric is to use PTMG, PPC or PBA as its soft segment, respectively;5.0%(w/w)dimethylol propionic acid (DMPA);20.0%(w/w) AEAPS; and an R value of1.4. Moreover, theWPU has excellent film-forming and wrapping performance onto the cashmere fiber surface. AWPU with a crosslinked structure is obtained after being modified with AEAPS, and this isbeneficial for improving the anti-pilling properties of the treated fabric. The gathering ofpolysiloxane chains on the film surface is helpful in improving the handle of the treated fabric. Inaddition, the modification of WPU by using AEAPS has a positive effect on the anti-pillingproperties, handle, and washing resistance of the treated fabric. When the amount of WPUmodified by AEAPS, with PTMG, PPC or PBA as its soft segment, respectively, is2.0%(owf),the degree that the treated fabric can resist pilling is increased to4on a scale that indicatesresistance to pilling, while that of the untreated fabric ranks only2-3. Among the WPU modifiedwith AEAPS that uses PTMG, PPC or PBA as the soft segment, the WPU emulsion with PTMGused as the finishing treatment provides the most soft fabric, and the handle of the cashmereknitted fabric treated with this type of WPU is almost the same as that of the untreated fabric,which reaches a3on the measurement scale. Furthermore, the negative effects found on thehandle of the WPU treated cashmere knitted fabric can be avoided through the modification ofWPU with AEAPS.3. Influence the structures of amino silicone oil on performance of modified WPU asanti-pilling finishing agent for cashmere. PTMG is used as the raw material of the soft segment inthe preparation of WPU, then AEAPS and PBS with different ammonia values are used,respectively, in the preparation of WPU modified with these two silicone oils, and then finally, the modified WPU is applied as an anti-pilling finishing agent onto cashmere knitted fabric. Theinfluence of the structure of the silicone oil on the WPU structure and emulsion as well as thelatex and finishing properties is then investigated.It is found that with an increase in the ammonia value of the AEAPS, the crosslinkingfunction of the WPU is enhanced, but the stability of this type of WPU emulsion is reduced. Thewater resistance and mechanical strength of the WPU latex modified with AEAPS are improved,while micro-phase separation is reduced, and the gathering of polysiloxane chains on the surfaceof the WPU latex tends to be strong. With an increase in the ammonia value of the PBS, thecontent of the hydrophilic polyether chain segments increases in the molecular chain, while thecrosslinking function of PBS is weak, thus the emulsion stability of the WPU modified with PBScan be improved. The water resistance of the latex is reduced, and the influence of the ammoniavalue of PBS on the micro-phase separation and the gathering of polysiloxane chains on WPUlatex surface is minimal. The molecular weight, mechanical strength of the latex and the gatheringof polysiloxane chains on the surface of the WPU latex modified with AEAPS are significantlygreater than those of WPU modified with PBS.The properties of the cashmere knitted fabric treated with WPU that has been modified withamino silicone oil show that the silicone oil type and ammonia value have no obvious influence ondegree of fabric pilling. In terms of anti-pilling, the performance of WPU modified with PBS andAEAPS respectively is basically the same. However, the gathering of polysiloxane chains on thesurface of the WPU latex and hardness of the latex itself are the key factors that influence thehandle of the treated fabric. The increase in the gathering of the polysiloxane chain segments onthe surface of the WPU latex has a positive effect on the handle of the treated fabric, but anegative effect on the handle of the treated fabric is unavoidable when the latex hardness isincreased. Furthermore, WPU that is modified with PBS has obvious advantages in comparison tothat modified with AEAPS in terms of the handle of the treated fabric. When the cashmere knittedfabric is jointly treated with PBS and WPU that has been modified with PBS, the anti-pillingproperty is excellent and the degree of resistance to pilling has a rating of4, while the handle isfluffy and soft, and ranks4on a scale for handle. Moreover, the air and water vapor permeabilities,antistatic property and washing resistance of the treated fabric are ideal. As well, its finishingproperties are superior to the finishing properties obtained by other commonly used finishingtechniques in the cashmere industry.4. Preparation of linear PBS modified cationic WPU as anti-pilling finishing agent forcashmere. A cationic WPU (CWPU) prepolymer is obtained when PTMG is used as the rawmaterial of the soft segment and N-methyl diethanolamine (MDEA) as the hydrophilic chainextender. A silicone modified CWPU is synthesized by using PBS as the modifier, and theinfluence of CWPU on the anti-pilling of the treated cashmere knitted fabric is investigated.When the R value is1.4, the MDEA content is6.0%(w/w), BDO content is5.0%(w/w) andPBS content is20.0%(w/w) in the preparation of the CWPU, the stability of the obtained CWPUemulsion is good, hardness of its latex is low, and adhesion strength and water resistance of itslatex are optimal. The particle size of the CWPU emulsion increases with the introduction of PBSinto the WPU, but when the PBS content is controlled within20.0%(w/w), the stability of theemulsion is good. With an increase in the PBS content, the gathering of polysiloxane chains on thesurface of the film tends to be stronger. When the PBS content is20.0%(w/w), the latex surface iscompletely covered with polysiloxane chain segments, therefore, oxidation yellowing of its latex can be reduced in a certain extent. The properties of the cashmere knitted fabric treated with theCWPU emulsion show that an increase in the R value, and the MDEA and PBS contents havepositive effects on the anti-pilling of the treated fabric, and PBS content increases are helpful forimproving the handle. When the cashmere knitted fabric is treated with both a CWPU emulsionand PBS, the degree of the anti-pilling, handle, air and water vapor permeabilities and antistaticproperty of the treated fabric are almost the same as that of fabric jointly treated with PBS and ananionic WPU emulsion modified with PBS. However, obvious yellowing occurs when CWPUmodified with PBS is used as the finishing agent for cashmere fabric.