Presentation on theme: "INVESTIGATION IN THE MANUFACTURE OF NON-WOVENS FROM POLYLACTIDE BY SPUNBOND METHOD K. Sulak 1, M. Lichocik 1, T. Mik 1, I. Krucińska 2, M. Puchalski 2,"— Presentation transcript:
INVESTIGATION IN THE MANUFACTURE OF NON-WOVENS FROM POLYLACTIDE BY SPUNBOND METHOD K. Sulak 1, M. Lichocik 1, T. Mik 1, I. Krucińska 2, M. Puchalski 2, J. Jarzębowski 3 1 Institute of Biopolymers and Chemical Fibers, M. Skłodowskiej-Curie 19/27, 90-570 Lodz, Poland, e-mail: email@example.com@ibwch.lodz.pl 2 Technical University of Lodz, Faculty of Material Technologies and Textile Design, Department of Fibre Physics and Textile Metrology, Żeromskiego 116, 90-924 Lodz, Poland, e-mail: firstname.lastname@example.org@p.lodz.pl 3 Research and Development Centre of Textile Machinery “Polmatex-Cenaro”, Wólczańska 55/59, 90-608 Lodz, Poland BACKGROUND Poly(lactic acid) or polylactide (PLA) is an aliphatic polyester that can be produced from renewable materials such as corn, sugar or vegetables 1,2. The production of PLA is based on the polycondensation of lactic acid or the ring-opening polymerisation of lactide obtained from the depolymerisation of oligomers of lactic acid, which is a product of the fermentation of biomass such as corn. In comparison with conventional polymers, which are produced from petroleum, PLA is an environmentally friendly biodegradable polymer, and it has attracted increased attention in recent years. However, due to high manufacturing costs, the use of PLA has been limited for many years to medical applications 3,4,5. A decrease in the price of PLA expands the range of possible applications. For example, PLA has become a major starting material in the manufacture of biodegradable textiles 6. The preparation, structure and properties of products made of PLA and its modification are the subjects of intensive scientific 7 and technological investigations. Compared with classical polyesters such as polyethylene terephthalate (PET), PLA products are characterised by a higher water sorption of 0.4-0.6% and better resistance to UV radiation. The latter feature, in combination with biodegradability, makes polylactide fibres and non-woven fabrics particularly useful raw materials for the preparation of disposable medical and hygiene textiles. Other applications include technical textiles used in filtration or in agriculture and in cloth for garments and underwear. The ability of PLA to crystallise depends strongly on the stereochemical form of PLA and is different for isotactic poly(L-lactide) (PLLA) or poly(D- lactide) (PDLA), syndiotactic poly(meso-lactide), atactic poly(meso-lactide) or poly(D,L-lactide), PLLA/PDLA stereocomplexes and copolymers with random levels of meso-, L-, and D-lactide. As a consequence, the physical properties of fabrics manufactured from different PLAs can be differ. Moreover supermolecular structure of PLA fabrics strongly depends on the stereoregularity of the PLA form of the polymer and the technological conditions applied during the fibre manufacturing process. Therefore, it is important to elucidate the relationships between the conditions of formation and the properties of the resulting fabrics. A B AIM OF WORK The aim of work was to determine the influence of different forming parameters (especially thermal conditions of stabilisation at the embossing roll of the calender) on the physical and mechanical properties and supermolecular structure of PLA spun-bonded nonwoven fabrics. ACKNOWLEDGEMENT The presented research was performed within the framework of the key project titled “Biodegradable fibrous products” (acronym: Biogratex) supported by the European Regional Development Fund; Agreement No. POIG.01.03.01-00-007/08-00. MATERIALS AND TEST METHODS Raw material Non-woven fabrics were manufactured from commercially available PLA 6251D (Nature Works LLC, USA) specifically designed for the spun-bonded technology. A molar mass of PLA 6251D Mn of 45 800 g mol-1 and a polydispersity M w /M n of 1.29 were determined by size-exclusion chromatography (SEC) with a multi-angle light scattering (MALLS) detector in methylene chloride. The D-lactide content was 1.4%, as determined based on the specific optical rotation measurements. The glass transition temperature (T g ) and melting temperature (T m ), determined by differential scanning calorimetry (DSC), were equal to 61°C and 128°C, respectively. Drying of polymer To reduce the moisture content below 50 ppm, prior to spinning, the PLA was dried for at least 4 h at 80°C (dew point -30°C) in a Piovan dryer that is part of the laboratory setup for studying non-woven fabrics manufacturing with the spun-bonded technique. The moisture content in the polymer was measured by the Karl Fischer coulometric method using the DL39X apparatus (Mettler Toledo). Spun-bonded technology details The non-woven fabrics were formed by a spun-bond technique on a laboratory line designed and constructed by the Research and Development Centre of Textile Machinery Polmatex-Cenaro, Poland. The process parameters were as follows: a temperature in the range from 205°C to 216°C and a polymer throughput in the range of 0.10-0.43 g/min/hole can be used. A spinneret with 467 holes was used. The calender temperature was varied from 60°C to 130°C. Thermal properties For characterisation of the thermal properties of fabrics formed under the various manufacturing conditions, DSC measurements were carried out using a Q2000 (TA Instruments, UK). Specimens were first heated from 0 C to 250 C and then cooled to -30 C and immediately reheated to 250 C at a rate of 10 C/min. Mechanical properties The tensile strength and elongation analysis of the studied spun-bonded fabrics was conducted using the mechanical testing machine Instron 5511 according to EU standard EN 29073-3:1992 “Methods of test for nonwovens. Determination of tensile strength and elongation”. Shrinkage analysis The changes in the dimensions of the non-woven fabrics in hot air (both the length and width) were determined in accordance with standard ISO 3759:2011 “Textiles - Preparation, marking and measuring of fabric specimens and garments in tests for determination of dimensional change”. RESULTS Structural properties of PLA spun-bonded non-woven fabrics Mechanical properties of PLA spun-bonded non-woven fabrics Table 1. DSC calorimetric data obtained for the investigated variants of spun-bonded, non-woven fabrics. Temperature of calender (°C) Degree of crystallinity (wt. %) Glass transition temperature T g,(°C) Cold crystallisation temperature T c, (°C) Melting temperature T m,(°C) Enthalpy of cold crystallisation H c, (J/g) Change in heat capacity ΔC p, J/g°C) Enthalpy of melting H m (J/g) 7021667616628.32.5247.9 7520667516729.92.1248.8 8040668016610.90.6947.9 855466-165-0.3449.6 905465-165-0.1950.3 955565-165-0.2951.1 1005465-164-0.3450.1 1055464-164-0.1750.7 1105665-164-0.2252.3 1205664-164-0.1751.1 1305564-164-0.1550.0 Fig. 1. DSC thermograms recorded during the first heating Fig. 2. Relationships between the calculated degree of crystallinity and the change in heat capacity (ΔCp) for each sample stabilised at different thermal conditions. The data in Table 1 and Figure 2 clearly indicate that the elevation of the stabilisation temperature to 85°C markedly increased the crystallinity level of the fibres, which limited or even eliminated the possibility of cold crystallisation during heating. Fig. 3. Changes of the mechanical properties of non–woven fabrics stabilised at different thermal conditions in the machine (MD) and transverse (TD) directions: a) tenacity of non-woven fabrics and b) elongation at break of non- woven fabrics. Fig. 4 Changes in the length of the investigated samples in the machine direction as a function of the stabilisation temperature. When the stabilisation temperature rises above 85°C, the degree of crystallinity increases to a maximum value of approximately 55%, the overall molecular orientation increases and the ordered α crystals are developed. The development of such a supermolecular structure results in stability of the fabric dimensions in hot air. CONCLUSION Results showed the rebuilding of the supermolecular structure of the investigated samples of PLA fabrics under the influence of different stabilisation temperatures adjusted at the embossing roll in the range of 70- 130°C. The crystallinity degree increased to 54% when the temperature of the calender was changed to 85°C. Further increases of the stabilisation temperature did not have any significant influence on the crystallinity degree of the tested samples. The increased crystallinity level was reflected in the reduction of thermal shrinkage and in the increase of the stress at the breaking point of the investigated samples. The maximum value of the stress at the breaking point was observed for PLA non-woven fabrics stabilised at a temperature of 90°C. The stabilisation of non-woven fabrics in the optimum temperature range of 85-100°C made it possible to reach high values for the stress at the breaking point and small values of thermal shrinkage. 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