Color Masterbatches for Polyamide 6 Fibers. Optimization of Compounding and Spinning Processes
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XXVI cycle XXVI cycle Doctoral School in Materials Science and Engineering Color masterbatches for polyamide 6 fibers. Optimization of compounding and spinning processes. Physical-chemical characterization of industrial products. Mauro Buccella April 2014 XXVI cycle XXVI cycle Doctoral School in Materials Science and Engineering Color masterbatches for polyamide 6 fibers. Optimization of compounding and spinning processes. Physical-chemical characterization of industrial products. Mauro Buccella Academic Tutors: Prof. Luca Fambri Ing. Andrea Dorigato, PhD Industrial Tutor: Dott. Mauro Caldara April 2014 Abstract ABSTRACT In the last years the coloration industry has become increasingly important because it strongly influences the market of the plastic materials. The request of objects with new and particular colors, sometimes with imperceptible differences, combined with high physical and chemical performances, has made the coloration technology more sophisticated and complex. Moreover, the recent legislations (i.e. REACH standard) suggest the use of products with lower human health impact. Therefore, a continuous research and development of new colorants and technologies is needed, in order to obtain environmental friendly manufacturing processes and market products. As concerns the carpet sector, the solution dyed process of the fibers is industrially preferable rather than the coloration through batch of raw yarns. This is because the first process involves the production of monoconcentrated color masterbatches, their mixing in order to obtain the final color masterbatch and its addition into the polymer matrix during fiber spinning. On the other hand, the production of carpet from raw fibers shows higher environmental impact because the dyeing baths contain colorants and additives environmentally harmful and difficult to remove with water treatments. The solution dyed process is more difficult from an industrial point of view, because during the melt spinning three problems can occurred: (i) clogging of filtration system during spinning due to agglomerates, deposits and degraded material, (ii) formation of polymer drops under the spinneret due to degradation phenomena that can cause premature fibers breakage and (iii) fibers breakage during drawing process. The objective of this work is the investigation of the industrial production process of the Color Masterbatches and of the parameters that influence the pigment dispersion into the polymer matrix. In particular, the project is focused on the production Abstract process optimization in order to increase the quality of the final product and to minimize their environmental impact. The three steps of the solution dyed bulk continuous process were investigated: (i) production of monoconcentrated masterbatch, (ii) production of color masterbatch and (iii) mass pigmentation during melt spinning process. In the first part of the work, a detailed microstructural characterization was performed to assess the different morphologies and surface properties of the most important color pigments used in the automotive sector. The most problematic monoconcentrated masterbatches were industrially produced using different processing set-up, related to different specific mechanical energy applied to the material during the production. Furthermore, a detailed analysis of the pigment dispersion state in the matrix was performed, through the evaluation of the filterability, the Relative Color Strength (RCS) and the rheological behavior of the monoconcentrated masterbatches. Moreover the thermal stability of the products was investigated by chemical characterization and rheological measurement. The industrial production process for each monoconcentrated masterbatch was optimized, obtaining a product quality improvement and a significant production cost reduction. In the second part of the work, the blue color masterbatch was selected because it is a critical product for the melt spinning process. This color masterbatch has the peculiarity to clog the filtration system during spinning process, and a frequent change of filters is thus required. This monoconcentrated color masterbatch was produced in two different ways: standard and optimized processes. These two color masterbatches were fully characterized, from a coloration, chemical and rheological point of view, in order to determine the effect of monoconcentrated production process and so of the pigment dispersion on the subsequent industrial production step. The use of the optimized monoconcentrated masterbatch allowed to Abstract reduce the clogging power of the product of about 30%, and to increase its thermal stability. Furthermore even the monomer concentration, that is related to the drop formation under the spinneret and to the filament breakage, was reduced. The third part was focused on the characterization of the industrial yarn colored with the standard and the optimized blue masterbatches, in order to evaluate the effect of the pigment dispersion on the final products. The optimized yarn showed an improvement of the mechanical properties, in particular of the elastic modulus, compared with the standard product. This is very important because, for the yarns used in the carpet industry, the higher elastic modulus, the higher carpet resistant to the compressive stresses during its service life. The pigment dispersion improvement enhanced the heterogeneous nucleation activity of polyamide 6 during the melt spinning, resulting in a higher content of the more stable α phase compared to the γ crystalline phase. The thermal and UV degradation resistance were also improved. Finally, in order to confirm the good experimental results obtained on the optimized blue yarn at the laboratory scale, an industrial test was performed and the most problematic aspects of the process were critically analyzed. The use of the optimized blue masterbatch to color the industrial yarn allowed to markedly reduce the clogging phenomenon on the extruder filter of about 70%, reducing the number of filter substitutions and so the production stops. Moreover, the filament breakage frequency during the spinning were reduce of about 45%, increasing the productivity of the process, the stability of the product and reducing the production co Table of Contents TABLE OF CONTENTS INTRODUCTION ............................................................................................ 1 1. BACKGROUND...................................................................................... 3 1.1. PHYSICAL PROPERTIES OF COLOR.......................................................... 3 1.1.1. ILLUMINANT ....................................................................................... 3 1.1.2. OBJECT ............................................................................................... 5 1.1.3. THE OBSERVER ................................................................................... 7 1.2. COLOR MATCHING ................................................................................. 8 1.3. COLOR MEASUREMENTS ...................................................................... 12 1.4. COLORATION TECHNOLOGY ................................................................ 13 1.4.1. PIGMENT PROPERTIES ........................................................................ 14 1.4.2. MASS PIGMENTATION OF SYNTHETIC FIBERS ...................................... 16 1.5. EXTRUSION PROCESS ............................................................................ 19 1.6. MELT SPINNING PROCESS .................................................................... 23 2. EXPERIMENTAL ................................................................................. 29 2.1. MATERIALS .......................................................................................... 29 2.1.1. POLYAMIDE 6 ................................................................................... 29 2.1.2. COLOR PIGMENTS ............................................................................. 33 2.1.2.1. White Pigment (PW6) ............................................................ 34 2.1.2.2. Black Pigment (PBk7) ............................................................ 35 i Table of Contents 2.1.2.3. Brown Pigment (PBr24) ........................................................ 35 2.1.2.4. Red Pigment (PR101) ............................................................ 36 2.1.2.5. Blue Pigment (PB15:3) .......................................................... 37 2.1.2.6. Green Pigment (PG7) ............................................................ 38 2.1.2.7. Violet Pigment (PV23) ........................................................... 39 2.1.2.8. Red Pigment (PR149) ............................................................ 40 2.2. MATERIALS PROCESSING ..................................................................... 41 2.2.1. MONOCONCENTRATED MASTERBATCH ............................................. 41 2.2.2. COLOR MASTERBATCH ...................................................................... 46 2.2.3. FIBER SPINNING ................................................................................ 48 2.3. EXPERIMENTAL ACTIVITIES ................................................................. 52 2.3.1. MICROSTRUCTURAL CHARACTERIZATION .......................................... 52 2.3.1.1. Density measurements ........................................................... 52 2.3.1.2. Evaluation of the pigment surface properties .......................