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PLA Processing Guide for Spinning FibersThis information is intended for use only as a guide for the manufacture of PLA fibers. Because melt spinning anddownstream processing of PLA fibers is complex, an experimental approach may be required to achieve desiredresults.1.0 Safety and Handling PrecautionsAll safety precautions normally followed in the handling and processing of melted thermoplastics should befollowed for NatureWorks PLA resins.As with most thermoplastics, melt processing and the variability of those conditions may result in minordecomposition. Lactide, a non-hazardous gaseous irritant, is a minor by-product of PLA melt processing.Appropriate air testing should be completed to ensure an acceptable Threshold Limit Value (TLV) of less than 5mg/m3 is maintained. The use of process area point source remediation measures such as monomer fume hoods orexhausts near the spinneret are typically recommended.PLA is considered non-hazardous according to DOT shipping regulations. When handling PLA resin at roomtemperature avoid direct skin and eye contact along with conditions that promote dust formation. For furtherinformation, consult the appropriate MSDS for the PLA grade being processed.2.0 Pellet Storage and Blending RecommendationPLA resins should be stored in an environment designed to minimize moisture uptake. Product should also bestored in a cool place at temperatures below 50 C (122oF).Product that is delivered in cartons or super sacks should be kept sealed until ready for loading into the blendingand/or drying system. Bulk resin stored in silos, hoppers etc for extended periods (more than 6 hrs) should be keptpurged with dry air or nitrogen to minimize moisture gain. In the case of outside storage, if the product is suppliedin Boxes or other non-bulk containers, the unopened container should be brought into the fiber production area andallowed to equilibrate for a minimum of 24 hours before opening.During chip transfer, minimal transfer air temperature ( 40C) and velocity ( 25 m/s for dilute phase transfersystems) are recommended to minimize the potential of generating fines.3.0 Resin Properties6201D is the recommended PLA resin grade for staple fibers. Typical properties of 6201D are shown in the tablebelow.Resin PropertyRVMelt Temperature (oC)Glass Transition Temperature (oC)Crystallization Temperature (oC)Version 1.0Nominal Value3.0 – 3.2165 – 17355 – 62100 - 1203/15/05

Typical PLA Resin PropertiesThe graph on the following page shows the melt density of PLA over a wide temperature range.P L A M e lt D e n s ity C u rv e1 .1 6 01 .1 5 01 .1 4 0Melt Density (g/cc)1 .1 3 01 .1 2 01 .1 1 01 .1 0 01 .0 9 01 .0 8 01 .0 7 01 .0 6 01 .0 5 0140150160170180190200210220230240T e m p (o C )Version 1.03/15/05250

The rheology curves are shown in the following graph.6200D Rheology, 240CShear Viscosity, Pa.s10006200D, 2.8 RV6200D, 3.1 RV6200D, 3.4 RV1001010100100010000100000Shear Rate, /sec.4.0 Materials of ConstructionAll metal parts in the extrusion process should be constructed of stainless steel to minimize corrosion. Furthermore,PLA should not be left in the extruder, polymer filter, polymer transfer lines, spin beam, spinnerets or any other partof the extrusion system at PLA melt temperatures or higher for extended periods. Below is a guideline for therecommended types of steel that should be used in the extrusion system.PartSteel TypeMelt pumps and bearingsPump blocksTransfer lines and spin beamSUS440BSUS631SUS440C5.0 DryingPLA resin can be successfully dried using most standard drying systems. Recommended conditions are provided forstandard desiccant based column dryers. For other drying system designs, additional information can be providedupon request.To prevent equipment corrosion, it is not recommended to dry or store hot PLA resin in carbon steel vessels (seeSection 2.0).Version 1.03/15/05

In-line drying is essential for PLA resins. A moisture content of less than (50 PPM) is recommended to preventviscosity degradation. Material is supplied in foil-lined containers dried to less than 400 PPM as measured byNatureWorks internal method. The resin should not be exposed to atmospheric conditions after drying. Keep thepackage sealed until ready to use and promptly dry and reseal any unused material. The drying table below can beused to estimate the drying time needed for PLA. Air or nitrogen based desiccant drying systems can be used at therecommended temperatures. Typical PLA drying conditions are shown in the table below.Drying ParameterResidence Time (hours)Air Temperature (oC)Air Dew Point (oC)Air Flow Rate (m3/min/kg resin)Typical SettingsAmorphousCrystalline4250100- 40- 40 0.031 0.031Typical PLA Raw Material Drying ConditionsTypical desiccant dryer regeneration temperatures exceed the melt point of PLA resins. To prevent issues withpellet bridging, sticking or melting, the drying system should be verified to ensure temperature control is adequateduring operation as well as during regeneration cycles since valve leakage is common in many systems.6.0 Melt SpinningPrior to introducing PLA into any melt spinning system, the system should be properly purged to prevent anypolymer contamination and spinnability problems from occurring. The purging procedures below are recommendedfor optimal removal of other polymers.6.1 PLA Purging Procedure1.2.3.4.5.6.7.Purge with a low MI ( 1) PP at normal PET (280oC) operating temperatures without spinneret in place.Purge for at least 30 minutes, until polymer appears free of contamination. Let system empty as well aspossible.Reduce extrusion temperature settings to normal PLA operating temperature (230 – 240oC).Begin purging with an 18 MI PP without spinneret in place while temperature is dropping.After temperature targets are achieved, purge for at least 30 minutes, until polymer appears free ofcontamination. Let system empty as well as possible.Transition to PLA and purge for at least 30 minutes, until polymer appears free of contamination.Insert pre-heated spinneret and allow temperature to equilibrate.Purge with 6201D and evaluate flow from capillaries. As long as flow is even from each capillary andthere is no evidence of contamination, begin spinning.Important Notes:1.2.It is critical that all drying and conveying/receiving systems be free of all PET or PP and is vacuumed toensure that there is no remaining polymer dust, before adding PLA. PET will not melt at PLA operatingtemperatures and will block screens, if it is present in the systemBrand of PP used for purging is unimportant, as long as it does not thermally cross-link.6.2 ExtrusionA general-purpose single-screw extruder, 24 to 36:1 L/D with feed-throat cooling is acceptable for processing PLA.A mixing tip is generally recommended along with static mixers in the product line to ensure temperature uniformityas well as optimum additive dispersion and melt polymer homogeneity. The following table shows a typical meltprofile for PLA.Version 1.03/15/05

Extrusion AreaMelt Temperature Setting (oC)Feed throatZone 1Zone 2Zone 3Melt pumpSpin head25200220230235235Typical PLA Extrusion ConditionsNote 1: Temperatures are only starting points and may need to be altered. Target PLA melt temperatures (after meltpump) should be in the range of 235 5 CNote 2: PLA resins should not be processed at temperatures above 250 C (482 F) due to excessive thermaldegradation.6.3 AdditivesDelusterants such as TiO2 are best added as a masterbatch at 15-30 wt% in PLA resins and controlled dosing therequired amount of dried masterbatch into the feed throat of the running extruder.6.4 FiltrationPLA resin will be provided pre-filtered to a level of 20 microns. The following pack makeup is recommended:Loose media (optional - depending upon pack configuration) 200-350 micron shattered metal is recommended for anuncompressed pack cavity fill.Screens – cascade configuration with appropriate support screens is recommended with finest filtration level of 20microns.6.5 Heating SystemsTo allow for the required temperatures to be obtained in spinning, typically vapor heat transfer system mediumchanges are required. Dowtherm J / Therminol LT or a comparable vapor HTM which has an atmosphericboiling point of 200 C or less while remaining within specific system pressure design limits is generallyrecommended. Operation of the HTM system at a temperature as close as possible to the actual melt temperature(235 5 C) is recommended to provide an adiabatic spinning system. For vacuum assisted systems, typically heattransfer medium changes are not required as long as the system vacuum can be operated at a level to providevaporization and uniform heating at the suggested temperatures (230-240 C). Prior to being placed into service,spin packs should be heated to 250oC to allow for some temperature loss during spin pack installation.Version 1.03/15/05

6.6 SpinneretsRecommended capillary dimensions for a fiber with a solid round cross section range from 0.2-0.35 mm diameter,typically with a 2 to 3:1 L/D ratio. Larger capillaries may be necessary for fiber’s greater than 6 dpf. The followingguide can be used to estimate spinneret requirements based on spun product dpf:Spinneret Capillary Sizing0.4diameter mm0.350.32 L/D0.253 L/D0.20.150246810spun dpfCapillary dimensions for modified cross sections will deviate greatly from solid round fibers. They should bedesigned to meet the desired fiber shape, while providing adequate pressure drop to ensure good denier uniformityand adequate draw down or stretch ratio to facilitate good spinning performance.6.7 QuenchingFilaments should be quenched with air at controlled temperatures and velocities to ensure good denier andorientation uniformity. Typical quenching conditions are shown below, but quenching conditions need to beoptimized by product depending upon the denier, spinneret design, and cross section.Quench parameterTypical TargetQuench Air velocity (m/s)Quench Air Temperature (oC)Monomer Exhaust Velocity (m/s)Spacer or Shroud Length (mm)0.26 – 1.510 – 20.26 – 2.050 -100Typical PLA Quenching ConditionsA monomer exhaust system is preferred to prevent the buildup of residual lactide around the spinneretface and quench screen.6.8 Take UpPLA can be spun over a wide range of take up speeds, but typically runs between 1100 and 1850 m/min.7.0 DrawingA modern polyester type draw line equipped with accurate speed, temperature and tension controls is recommendedfor drawing PLA. Two-stage drawing is preferred to maximize tensile properties without stress whitening PLA.Fleissner and Neumag manufacture suitable draw lines for PLA.Version 1.03/15/05

When running on older lines, draw ratios that can be achieved will depend on the degree of control overtemperatures, both water and steam, the type of draw roll heating employed, the length of water baths and steamchests and the line speed.In short, uniform drawing depends on heat transfer rates from the equipment to the fibre and the degree of controlover drawing temperatures and conditions. Several factors impact the heat transfer rate, including:Tow massInitial tow temperature.Line speedContact area of the rolls (diameter) and layoutNumber of rollsMethod of heat application (immersion bath, sparge systems)7.1 Creeling and pre-tensioning7.1.1 Creel SizeCreel size is largely dependent upon the crimper size and the tension rating of the drawstands. PLA can be run atsimilar tow densities in crimping as PET, with typical densities ranging from 65 to 72 thousand dtex per cm ofcrimper width.7.1.2 Creel TensioningCreels should be designed to provide a minimal tension level on each subtow in the creel. If the tension is too great,typically greater than 0.2 g/den, the tow could begin drawing before or during immersion in the pre draw bath,causing excessive denier variation along with the possibility of broken fibers and high wrap rates. In addition, thetension level between individual subtows in the creel should be uniform. An adjustable pre tension stand is preferredprior to the pre draw bath to assist in equalising the tension between subtows.7.2 Pre Draw BathPre-draw baths should be sufficiently long to enable saturation of the tow with moisture and finish and to initiallyraise the tow temperature to 25-50oC. The tow should not be heated above PLA’s Tg (58oC), other wise the towcould begin drawing, which would lead to the same types of problems described in the preceding section. Also niprolls are recommended on the pre draw rolls to minimize tension on the towband before drawing.7.3 Drawing7.3.1 TemperaturesThe initial drawing occurs in the first draw stage, where the tow temperature should be maintained between 45 and70oC. Roll cooling is recommended on the post draw stand to prevent the tow band from sticking to the rolls. Therecommended tow temperature for the second draw stage is 70 – 90oC. Failure to reach recommended temperaturesin stage-2 draw zone would result in fiber with an excessive amount of shrinkage once the fiber is heatset underrelaxed conditions.To achieve the recommended tow temperatures, heating systems between the draw are required. Where sparge typeheating systems are employed, the volumetric flow rate, distribution and temperature uniformity of the steam orwater are critical to ensuring uniform tension and drawing across the towband. Inadequate flow and/or poordistribution will lead to poor tow temperature uniformity, resulting in non uniform drawing and potentially brokenfiber and/or undrawns. Immersion baths also provide good tension and drawing uniformity, provided that they havegood temperature control and adequate circulation capabilities.Version 1.03/15/05

7.3.2 Draw RatiosPLA can be drawn over a wide range of draw ratios. The optimal draw ratio is dependent upon the type of polymerused, the as spun orientation level, and the desired tensile properties for the product. PLA staple fiber is typicallydrawn in the 3:1 – 4:1 range. As mentioned