Regardless of the fact that yarn hairiness changes to some extent during knitting,the hairiness of the yarns incorporated into knits has not been tested,since drawing the yarns from the knits and their winding on a spool before hairiness monitoring would additionally change the surface geometry of the yarns.To assess the vulnerability of the surface of the yarns,the hairiness monitor device was coupled with the apparatus Staff Tester G555A which was designed to subject the yarn to self-friction.The tester enabled self-abrasion of the yarn travelling at 50 m/min speed in a form of a right loop because the yarns were twisted in Z direction.Fibres falling off the self-rubbing yarn were collected on the filter beneath the “travelling” loop.Measuring head of the hairiness tester was fixed on the yarn path after the abrasion point in order to register the hairiness of the abraded yarn.The hairiness modification was expressed by the ratio of the number of hairs before yarn self-abrasion to that after self-abrasion.Yarn attrition produced by its self-abrasion was determined as the percentage of weight loss in relation to the weight of 100 m long pristine yarn.Liveliness of the yarns or the snarling tendency was taken as a measure of their relaxation ability which was quantified by the parameter – snarling distance.This is a distance between two approaching yarn ends at the moment the open loop begins to snarl.Apparatus,which was described in detail elsewhere enabled a movable end of the horizontally placed yarn sample,to approach to the other fixed end until the first snarls occurred.Thirty tests per yarn were conducted and the results were expressed as the mean value of the snarling distance.
The single jersey knitted fabrics were produced from the one- fibre type containing yarns which were assembled on a knitting machine and fed simultaneously,side by side through the same hole in the feeders to the needles.This method is similar to plating technique,indoor cannabis grow system but unlike plated structure,two yarns are randomly arranged on the face or back of the knit.Two yarns can also be wound on the same spool before knitting.The hemp/PAN blended knitted fabric was produced by feeding one hemp and one PAN yarn.The blending ratio was 50% hemp/50% PAN since both hemp and PAN yarns had the same size.Pure hemp and pure PAN knitted fabrics were produced with the same specifications to make a comparison with the hemp/ PAN blended knit.The single jersey fabrics were knitted on a 30” E20 Fouquet circular knitting machine with 1884 total needles and positive yarn feeding system at St.George Company.The knitted fabrics were kept under the standard atmospheric conditions for 72 h for relaxation,and then the pieces of the knits from which the clothing items were formed,were well rinsed with warm water and line dried at room temperature so as to release tensions and to relax their structure.The construction characteristics of the wet relaxed knitted fabrics are presented in Table 2.Knitted fabrics have gained in popularity thanks to their intrinsic stretch offering the freedom of movement and better tactile comfort to garments,especially for the next-to-skin ones.However,the dimensional behaviour of knitted fabrics is quite complicated and should be taken into account when designing garments.A number of factors are responsible for dimensional changes in knitted fabrics and these all are associated with fibre and yarn characteristics,knitting and finishing.
However,the most responsible factors in dimensional changes are known to be the swelling of yarn and relaxation of internal stress imposed on the yarn during knitting.Research findings indicated that dimensional changes in knitted fabrics take place up to five,six or seventh cycles of washing and drying.However,it seems that knitwear industry has found multi-cyclic relaxation procedure far too expensive regarding the work and time spent.Therefore,industrial practice implies a single cycle of washing and drying of knitted fabrics as a mean of structure relaxation,which is accepted as being adequate bearing in mind the fact that dimensional changes occur to the most extent during the first cycle.It has been shown in the wear trial conducted in the frame of the Starfish project that the shrinkage of garments is considerably lower than that measured on the corresponding garments laundered by laboratory washing procedure,which is explained by the fact that the garments are being re-stretched when wearing them in each subsequent testing cycle.Therefore,we considered it was enough for the tested undershirts to undergo ten wear and care cycles in our study.The hemp and PAN yarns,although having the same nominal linear density and twist,very slightly differed between each other in the measured values of these parameters,as can be seen in Table 1.However,the differences in the geometry of the yarns are more distinctive,which can be explained by different deformation properties of hemp and acrylic fibres.As a consequence of reduced flexibility of hemp fibres,due to which their movements during spinning were impeded,the hemp yarn was characterized by lower diameter than that of the acrylic yarn.This reduced migration of hemp fibres caused the yarn compactness to be higher,and hairiness to be much lower in respect to the acrylic yarn.In fact,the hairiness of the hemp yarn is unusually small for staple yarn which indicates its smooth surface.
Because of yarn tendency towards abrasion during the subsequent processing stages as well as when using the fabric,the hemp and acrylic yarns were assessed in terms of a change in hairiness after self-abrasion.The evolution of yarn surface geometry has an impact on the geometry of fabric surface,and consequently on its comfort properties.Both yarns are susceptible to changes in hairiness due to abrasion,but with different direction and the extent of modification.The hairiness of the hemp yarn was almost doubled after abrasion which is attributed to the stiffness of hemp fibre due to which they are pulled out onto the yarn surface during abrasion.The hairiness of the acrylic yarn decreased after abrasion for about 7%.It seems that this minor change in hairiness after abrasion resulted from the softness of acrylic fibres.Although the phenomenon of wetting fibres is beyond the scope of this study,some explanation is given in order to understand changes in construction characteristics of the yarns and knitted fabrics.The effect of water on fibres depends on their chemical composition.When wetting hydrophilic cellulose fibres,the hydrogen bonds between the molecular chains of cellulose relatively readily break and are formed again but with water molecules.These changes in the hydrogen bonding network lead to an increase in the fibre diameter which in turn resulted in the yarn swelling or in an increase in the yarn diameter.Recently,Jiang et al.explained hemp fibre swelling by the expansion of the cell wall caused by water molecules occupying the spaces between the microfibrils.Suh indicated that cellulose swelling caused,not only yarn diameter but also twist angle to increase,which imposed additional torsional stress in the yarn.These torsional stresses in the yarn alongside the residual stress due to its bending in a loop tend to reduce upon wetting which lead to distortion of the stitches and consequently to shrinkage of the knit.These physical changes in the cellulose fibres,yarns and knits made thereof remain to a certain extent after the fabric is dried,and therefore the yarn configuration in the stitches remains irreversibly changed.By comparing the geometry parameters for the hemp yarn before and after wetting of the knit,an increase of 4.5% in diameter and decrease in bulk density of the yarn can be noted.
This indicates the lower packing density of the hemp fibre in the yarn after wet relaxation of the knit.Lateral swelling of the hemp yarn during washing cycles in the wear trial test caused further increase in its diameter and decrease in bulk density.Due to low affinity of acrylic fibres for moisture absorption the acrylic yarn did not swell under wet relaxation,and therefore its diameter and bulk density were not changed.However,the increased diameter of the acrylic yarn was noted after the wear trial test.Bearing in mind the extremely low weight loss in self-abrasion of the acrylic yarn,we believe that acrylic fibre ends projecting from the yarn surface were clung to the yarn’ body increasing visually the yarn diameter instead of being worn out during the wear trial test.Wet relaxation of the knitted fabrics having different fibre content resulted in some differences in their construction characteristics,although they were knitted with the same technological parameters.The knitted fabrics differed to a large extent in stitch density which resulted from differences in their length and width wise shrinkage.This can be explained by relaxation of internal stress to which yarn is subjected during knitting and consolidation of structure due to yarn swelling.According to systematic research conducted by Allan Heap et al.,the process of releasing tension is fast and completes after one or two cycles,whereas the other process,which is attributed to structure consolidation,cannabis grow system is very slow and sometimes may be incomplete even after ten repeated launderings.Therefore,it is reasonable to believe that the construction characteristics of the knitted fabrics after undergoing the wear and care cycles are the results of their structure consolidation e changes in the shape of the loops and distortion of the loops out of the knit’s plane.In the applied experimental design,the structure consolidation was a consequence of complex interaction of two opposed processes.During the washing of the knitted fabrics,water is not just a swelling but also lubricating agent which reduces the friction at the interlocking points of the loops; the extra energy supplied by mechanical agitation during laundering helps the loops to overcome this frictional force and attain the minimum strain state.On the other hand,the knitted fabrics undergo mechanical deformation while wearing them in each testing cycle by which their structure suffer from certain changes.As can be seen in Table 4,the hemp knit shrank width wise meaning that wale density increased,but it stretched lengthwise as compared to the hemp/PAN knitted fabric whose course density did not change and wale density increased but to a lesser extent than that of the hemp knit.As a result,the surface stitch density of the hemp and hemp/PAN knitted fabrics increased.
As can be seen on SEM micrograph of the hemp knitted fabric,there was still sufficient void space left in the wale spacing after wet relaxation,which made it possible the higher width shrinkage during laundering cycles.These void spaces were less apparent in the wet relaxed hemp/PAN knitted fabric as illustrated by SEM micrograph on the Fig.1b,and therefore the less width shrinkage occurred after repeated wear and care cycles.Due to loops distortion with each subsequent cycle,the thickness of the hemp and hemp/PAN knitted fabrics was higher as compared to their thickness before the wear trial test.Changes in stitch configuration,i.e.an increase in loops density of the hemp and hemp/PAN knits caused an increase in their areal density.Well-balanced structure of the acrylic yarn and hydrophobic nature of acrylic fibre resulted in the unchanged stitch and areal density of the PAN knit.This is illustrated by SEM micro-graphs of the PAN knit before and after the wear trial test.Reduced thickness of the PAN knit resulted from lateral consolidation of its structure during the wear and care cycles.It has to be noted here that the increased diameter of the PAN yarn was registered by measuring the yarn pulled out from the worn knit.But when incorporated in the knit,the soft acrylic yarn is compressed in the interlacing points of the loops and cannot contribute to an increase in the thickness of the worn knit.The parameters describing the geometry of the knitted fabrics are presented in Table 5.As a consequence of the structural changes in the knitted fabrics during repeated wear and care cycles,their bulk density increased and porosity decreased.In addition,the increased stitch density of the hemp and hemp/PAN knits after undergoing the wear trial test indicated a larger number but smaller interstitial pores per unit area of the knit.A reduction in the interstitial pore size for the hemp and hemp/PAN knits after the wear trial test can be clearly seen in Fig.1.Bearing in mind the fact that in the wear trial test not only the stitch configuration of the knits but also geometry of the yarns changed,the parameters describing the knit geometry based on the geometry of both the knit and yarn were calculated.These are the stitch surface and stitch volume coefficients.The stitch surface coefficient correlates the stitch area and the area occupied by the yarn in the stitch indicating the size of open pores.