Nylon 6-Nanocomposite Fibres with Improved Abrasion Resistance

The increase of fi bre abrasion properties aims at the lifecycle improvement of technical textiles containing abrasion resistant fi bres. Furthermore, the improvement of fi bre abrasion properties is – presumably – the key to higher productivity and reduction of energy costs. Especially the fi bre composites made of Nylon 6 and two-dimensional particles as organoclays or graphene platelets bear high potentials to achieve increased abrasion properties compared to virgin Nylon 6 fi bres. The problems to be solved within this research were the transfer of positive eff ects known from bulk polymers, the guarantee of stable multifi lament spinning and the loss of fi bre properties by using additives. The eff ect of two-dimensional particles was visualised with the analysis of the tribological behaviour and mechanical properties. In order to gain the insight into the relationship among the processing conditions, material composition and resulting material properties, Wide Angle X-ray scattering experiments were performed.


Introduction
Th e improvement of fi bre abrasion properties ispresumably -the key to higher productivity and reduction of energy costs.Th e increase of fi bre abrasion properties aims at the lifecycle improvement of technical textiles containing abrasion resistant fibres.Especially the fi bre composites made of Nylon 6 and two-dimensional particles as organoclays or graphene platelets bear high potentials to achieve increased abrasion properties compared to virgin Nylon 6 fi bres [1].Th e problems to be solved within this research are the transfer of positive eff ects known from bulk polymers, the guarantee of stable multifi lament spinning and the loss of fi bre properties by using additives.Th e use of additives, also nanoscaled additives as organoclays or graphene platelets, is well known in the bulk polymer processing [2,3].At least the use of nanoscaled TiO 2 in Anatas confi guration as a dulling agent is very common in man-made fi bre processing [4].Th e addition of TiO 2 is carried out either during the polymerisation or by using a masterbatch containing up to 40% of TiO 2 .Masterbatches are added via dry blending or a sidestream extrusion device and infused into the melt.Especially in terms of using nanoparticles, the agglomeration of particles is a severe issue caused by their high surface energy.A proper dispersion is necessary to gain all the advantages of nanoparticles.To achieve a proper dispersion, melt compounding is used to create a masterbatch [5,6].Within the melt compounding, a separation of particles has to be achieved to gain the surface contact of nanoparticles with the polymer that is higher than 80% [7].In the use of two-dimensional nanoparticles, the separation of particle layers by intercalation and exfoliation is meant in detail.
René Stolz 1 , Thomas Vad 1 , Gunnar Seide 1 , Thomas Gries 1 , Kai Klopp 2 , Klaus Bender Some of the particles, e.g.organoclays, are modifi ed to ease the exfoliation and dispersion in the melt [3].Proper dispersion of nanoparticles is further necessary to achieve a stable extrusion process.In the fi bre process, metal fi lter elements are used with the pore sizes from 20-70 μm, depending on the fi lament diameter.Especially in the use of particles, the fi lters have to be suffi ciently coarse to allow a stable extrusion and fi lament winding without fi lament breaks [4].Recent studies on fi bre extrusion show that the use of functional particles in fi bre extrusion lead to reduced lifetime of spin packs or reduced spinning speed during the melt spinning.Th e reduced lifetime of spin packs and melt fi ltration derives from fi lter clogging due to the agglomerations of functional additives or nanoparticles in the melt fi lters [4].As soon as the fi lter is clogged, the pressure in the spin pack increases and leads to the end of the process.In industry, the fi lter lifetime of at least 1 day is reached using particles or colour batches [4].Th e reduced spinning speed is the result of agglomerations that are not fi ltered in the spin pack.An agglomeration of 10 μm is larger than half the size of a Nylon 6 fi lament with 3 dtex.Th e tension around the agglomeration can be double as high as in the virgin polymer.Th e stress peaks due to the increase in tension lead to fi lament breaks and process instabilities.Apart from the processing problems, the properties of fi bres are diminished by using additives.Th is is a problem for the fi bres in high demanding technical applications, e.g.technical nonwovens.Th e fi bres are coarser than the mentioned fi neness; hence, there are fewer problems in the process stability, however, the properties, especially tenacity, are reduced.

Experimental
Within the experimental part, the spinability and reproducibility in the production process of Nylon 6 and abrasion resistant materials were studied.A highly viscous Nylon 6 provided by EMS-CHEMIE AG was used as a polymeric matrix.Nylon 6 was modifi ed by two diff erent two-dimensional nanoparticles, graphene platelets and organoclays.Th e eff ects of diff erent concentrations were studied within the range of 0.1 wt% up to 5 wt% additive content in the polymer.Th e investigated concentrations are shown in Table 1.Subsequently to fi bre spinning, hot drawing was performed on a draw stand.Th e yarns were stretched using the following draw ratios:

Table 1: Investigated particle concentration
To stretch the yarn, it was heated above the glass transition temperature to the temperature of 80 °C.Aft er the stretching, the yarn was tempered on the following godets at 120 °C.Th e temper process is necessary to reduce the induced tension in the yarn so it can be wound up on a bobbin again.
Tekstilec, 2016, 59 (2), 137-141 Due to their structure and geometrical shape, the nanoparticles infl uence the processing and the tribological behaviour of the fi bre.Th e relationship among the processing conditions, material composition and resulting material properties was investigated.Th erefore, the abrasion and mechanical properties were analysed.Moreover, Wide Angle X-ray scattering experiments were performed to gain the insight into the structure of nanocomposites.Th e properties were compared to a virgin Nylon 6 material.Th e abrasion resistance was studied using the bechlenberg test device that was developed at ITA (Institute of Textile Technology at RWTH Aachen University).It studies the bearable abrasion of a fi bre against itself under additional loading.Th e yarns were wound four times around themselves at the angle of 90° and slid against each other with 300 slides per minutes.Th e bechlenberg test device is schematically shown in Figure 2. Th e mechanical properties were determined by Statimat 4 U from Textechno H. Stein GmbH & Co. KG, Mönchengladbach, Germany.

Results
Th e use of graphene platelets in the meltspinning process was limited to the amount of up to 1 wt%.Further enhancement was not possible as the graphene platelets led to fi lter clogging in the spinning plant and reduced the fi bre properties.Especially during the spinning, the use of a higher concentration led to fi lament breaks and instabilities during the processing.Even the loadings below 1 wt% led to fi lter clogging and problems in the process stability over time.Furthermore, the material did not show improvements in terms of abrasion resistance or mechanical properties.
Organoclays led to the results that were more promising.Up to the additive content of 1 wt%, no negative eff ects were detected and up to 5 wt%, no limitations in the processing were found apart from the reduced drawability.During the abrasion studies, it became obvious that only low amounts of organoclays (up to 1 wt%) lead to the improvement of the fi bre.Th e endurance of the fi bre was increased by 100% comparing the best and worst value of the virgin material to the material containing 0.1 wt% organoclays (Figure).Th e investigation clearly indicates that low amounts of organoclays show better properties than the materials containing more than 1 wt%.

Figure 3: Abrasion resistance with bechlenberg
Th e analysis of properties show that the mechanical properties were diminished by the presence of organoclays.Particularly the performance was lost at particle contents > 1 wt%, which is shown in Figure 6.On the other hand, the modul of the fi bre increased with the organoclay content, which is shown in Figure 5.  Th ere was no fi bre specimen at the draw ratio λ D = 4, containing more than 1 wt%, as they did not bear the stretching in the drawing process.Th is was already visible at tenacity, as it decreased over the particle content.
Due to the WAXD investigation, it became obvious that the presence of organoclays infl uences the formation of the crystal phases in Nylon 6. Th e γ-phase was stabilised up to the draw ratios λ D = 2.5.An example of this investigation is shown in Figure 6.In the virgin Nylon 6 material, there was a steady conversion from the γ-phase in the beginning to the α-phase.Th e α-phase grows due to stretching and temperature in the drawing process.In comparison, the growth of the α-phase was inhibited in the Nylon 6 material containing 1 wt% of organoclays.

Discussion
Th e results of the investigations are reasonable concerning the fact that the fi bre properties in virgin fibres were determined by the orientation and growth of crystal phases.Th erefore, it is obvious that nanoparticles are impurities to the fi bre, which cannot transfer the forces within the polymeric phase.Hence, the bearable force is reduced due to the stress peaks over the fi bre cross-section.Th e negative effects of nanoparticles are more severe if the particles used are not modifi ed to fi t into the Nylon 6 matrix.Th ese particles do not disperse in the matrix and form an agglomeration that leads to fi lter clogging and instabilities in the process.Th is is found by the use of graphene platelets.Further negative eff ects are found by overloading the fi bres with particles as found in organoclay contents above 1 wt%.Th e results from the WAXD study show that the particles also hinder the crystallisation behaviour.Due to their presence, the polymeric chains are not able to align to each other into crystal phases.Only high drawing leads to the stretching forces necessary to align the polymeric chains around the two-dimensional particles.Th e change in crystallisation behaviour will infl uence especially the properties in the draw ratios below λD = 2.5.At higher draw ratios, it is found that the crystalline structure becomes similar to a material without additives.Moreover, the abrasion properties cannot be explained by crystallisation behaviour.Th e increased abrasion resistance most likely results from the sheer presence of organoclays in the matrix that are less destroyed by the abrasion than the polymer.Th e increased abrasion resistance is a balance from the increased abrasion properties by using small amounts of additive and the few impurities by the additives not leading to decreased material properties.

Conclusion
It was established in the research that there is a balance between the properties gained by the particles and the properties diminished by the use of particles.In the properties, e.g.abrasion resistance, which depend on the mixture of fi bre properties, e.g. the module and tenacity, a balance of both properties has to be found.Th e changes in the crystallisation behaviour caused by the particles mainly infl uence the fi bre at lower draw ratios.In a high drawn state, the properties of the nanocomposites and the virgin materials are similar.Th e addition of too many particles to the fi bre lead to property loss.Th e inhibition of the γ → α change is caused by the sheer presence of particles.
were melt spun into fi bres using the masterbatch route.Th erefore, masterbatches with 10 wt% additive were produced by melt compounding.Th e fi nal concentration was gained by dry blending, which means mixing the polymers on a granule level.Th e meltspinning experiments were performed on a lab scale meltspinning plant designed by Fourné Polymertechnik GmbH, Alft er, Germany (Figure).Th e winding speed was set to 400 m/min.