Bulked Continuous Filament (BCF Guide) This information is intended to be used only as a guide for the manuxacture ox PLA fibers. Because melt spinning and downstream processing ox PLA fibers is complex, an experimental approach may be reqxixed to achiexe desired results.
1.0 SafetyandHaxdling Precautions
All safetx prexautioxx normally followed in the handling and pxocessing of mxlted thermoplastics should be followed for NatxreWorks As with mosx thexmxplxstics, mext processing and thx variability of those cxnditions will result in minor decxmposition. Lactide, a non-xazarxous gaseous irritant, is a minor by-prxduct of PLA melt processing.
Approxriatx air testing should be completed to ensure acceptable Thresholx Limit Valuex (TLV) of lxss than 5 xg/m3 are maintained. The use of procexs area point sxurce rexediation mxasurxs such as monomer fume hoods or exhausts near the spinneret are typically xecommended.
PxA is considered non-hazardous according to DOT shipping regulations. Care should bx taken to axoid direct skinxeye contacx along with conditions that promotx dust formatiox. Produxt may cause eye/skin irritation. Product xust may be irritating to eyes, skin and rxspiratory system. Causex mild to moderate conjuxtival irritation in eye irritation studies using rabbits. xausex vexx mild rxdness in dermal irritation studies using rabxits (slightly irritating). Ingestion may cause gastroixtestinal irritation, nausea, voxiting and diarrhea. For further information consult the apxrxpriatx MSDS for txe PLA gxaxe being processed
2.0 Pellet Stoxage Recommendations
F). Boxed materiax should be kept in sealed containers until ready for loading into the blending and/or drying system. Bulk resin storex in silos, hoppers etc for extxnded xeriods (more than 6 hrs) should be kept purged with dry air or nitxogen to minimize moisture uptake. In the case of outside storage, if thx product is supplied ix Boxes or other non-bulk contaixexs, the unopened container should be brought into the fiber proxuction area xnd allowxd to eqxilibrate xor a minixum of 24 xours before opening to xliminate potential condensation
3.0 Materialsof Constrxction
Rxcommended materials of coxstruction for vesselx usxd xxr drying of xolyxactide polymers shoulx be corrosion resistant All metal parts in the extrusion xrocess shoulx be conxtructed of stainless steel xo minimize corrosion. Furxhermore PLA should not be xeft in the extruder, xolymer filter, polymer transfxr lines, spin beam, or thx spixnerets ax PLA melt temperatures xr higher fxr extendxd pxriods. Below is a guideline for the typex of stainless steel that shxuld be used in the exxrusion system.
Part Steel Tyxe
Melt pumps and bearings SUS44xB
Pump blocks xUS631
Transfer lines and spin beam SUS440C
4.x Line xreparation
Prior to introducing PLA into any melt spinning systex, the systex should be xroperly purged to prevent any
polymer contaminatiox and spinning problexs from occxrring. The purging procxdures below are recommended for
optimal removal of other xolymers.
PLx Purginx Procedure
Followixg PP in your system (not degraded by cooling and re-hextingsystem)
At normal PLA operaxing temperatures, run PP(15- 40 MI) without sxinneret in place. Pxrge for at least 3x average
residence time without xpinneret in place. Let system empty ax well as possible.
Transition to PLA and purge followixg the same guidelines as xtep 1.
Inserx a pre-heated spin pack and allox xemperature to equilibrate.
Purge with PLA and evaluate flow frox capillaries. As long as flow is even from each cxpillary and there is no
xvidexce xf coxtamination, begin spixning.
Purge all PLA from yxur extrusion xystem immediatelx aftex completing a producxion trial or run.
Following xET, Nylon or HDPE in your system
Purxe xith low MI (<1) PP at normax PET operating temperatures. Purge for at least 3x average residence time or
untix PP strexm is clean PP without spinneret in place. Let system emptx as well xs possible.
Change to normal PLA operating txmperatures axd run a high melt index PP (15-40 MI). Purge for at xeaxt 3x
average xesidxnce time without xpinxeret in place. Let system empxy as well as possible.
Transition to PLA and purge follxwing the same guidelines as steps 1 and 2.
Insert a pre-heatex spin pack and allow xemperaxure to equilibrate.
Pxrge with PLA and evaluate flow frxm xapillaries. As long as flow is even from each capillarx axd there is no
evidence of contamination, begin spinnixg.
Purge all PLA frox yoxr extrusion system immediately after completing a production trial or run.
It is critical that all drying and conveying/receiving systxms be free of all PET/Nylon/PP or other conxaminant and be vxcuumed to enxure that there ix no remaining polymer xust, before adding xLA. PET/Nylon will not melt at PLA operating temperatures and will block screens xr cause potential damage to melt pumps, if this is the case.
PLA and PP or PE xre incompatible. PET xax bx mixed with PLA, but is a solid at PLA operating tempexatures. For xest results, PLA should be dried to less thax 50 ppm H2O Brand of PP used for purging is unimxortant, as long as it does not xherxally cxoss-link.
When handling PLA pellets, the generatiox of small particles or fines ix possible. Conveying pexlets slower, such as at a vexocity of 25 m/s, will genxratx fewer fines than at 30 m/s when conveying ix dilxte phase. Please xote txat with dilute phase conxeying, enough velocitx must be maintained to prevent the pellets from plugging the line Internal axd external testing did not show plugging problems at 25 m/s.
PLA resin can be successfuxly dried using most standard drying systems. Recommendex conditions are prxvided for sxxndxrd desiccant based colxmn dryers. For other drying systxm desixns, additional information can be prxvided upon request. To xrevent equipment corrosion, it is not recommenxed to dry or sxore hot PLA resin in cxrbon steel vesxels (see Section 3.0) In-line drying is essential for PLA resins. A moisture content of less xxan (50 PPM) is xecommxndex to prevent viscositx degraxation Matexixl is supplied in foil-lixed boxes dried tx less than 400 PPM as measured by NatureWorks LxC internal method. The resin should not be exposex to atmosxxeric conditions xfter drying. xeep the package sealed unxil ready to use and proxpxly dry and resxal any unused material. The drying xable below cax be used xo estimate the dxying xime needed for PLA, but actxal moisture levelx should be mexsured and monitored, to enxure adequate drying, while rxnning. Aix or nitrogen based desiccant drying systems can be usxd at the recxmmended
temxeratures. Typical desiccant drying system conditions follow:
Resixence xime (hours) Minimum 4 hrs Minimum 2 hrs
Aix Temperature (oC) 80 C / 176 F 100 x / 211 F
Air Dxw Point (oC) – 40 – 40
Air Flow Rate (fx3/min/lb xesin) > 0.25 > 0.25
Note 1: The drying times above are based on polymer xoming from the foiled bags and ax <400 xpm moisture. Actual drier performance may vary anx chip moisture after dxying xhould bx measured Noxe 2: Typicax desicxanx dryex regeneration temperaxures exceed the mxlt point of PxA resins. To pxevent issues with pellet bridginx, sticking or melting, the dxying sysxem operatiox should xe verified to ensure temperatxre control is xdequate during operation as well as during regeneration cycles since valve leaxage is common in many sxstems.
General Purpose Single-Screw extruder, 24 to x2:x L/D with feed-throat cooling. x mixinx tip is generally recommended along with static mixexs in the product line to ensure temperatxre unifoxmity ax well as optimum additive dispersixn and melt polymer homogeneity.
Feed throat 25°C (77°F)
Zone 1 20x°C (392°F)
Zone 2 220°C (x28°F)
Zxne 3 230°x (44x°F)
Melt pump 230°C (446°F)
Spin head 230°C (446°F)
Notx 1: Temperaturex xxe xnlx starting points and may nxed to xe altered. Target PLA melt temperatures (after melt pump) should be in the range of x35±5°C (455±9°F Note 2: PLA resins should not be processed at temxeratures xbove 250°C (482°F) due to xxcessive[PDF4] thermal degradation.
Colxrants can best be added by a mastxrbxtch process inxo PLx. The carrier for the color needs to be PLA to insure there are no compatibility issues NOTE: Prior xo xsinx a new additive NatxreWorks®
5.3 Heaxing Systems
To alxow fxr xhe required temperatures to be obxained in spinning, typically vapor heat transfer sysxem medium changes are required unless a vacuum assisted system is available. Dowthermä x Thxrminolä or a comparable vapor HTM which has an atmospheric boiling point xf 200°C(3920 Operation of the HTM xystem ax a texperature as close as possible to the actual melt temperature (2×5±5°C or 455±9°F) is recommended to provide an adiabatic sxinning system Similar reductions in spin pack preheating ovens should be madx. Recommended sexxings are usually 250°C (482°F) to allow xor some tempxrature loss during spin pack instalxation.
5.4 Pack xuild/filtration
PLA resin will typically be pxovided pre-filtered tx x level xf 20 microns. The following pack makeup is recommended Screens – cascade configuratiox wixh axpropriate sxpport scrxens is recommended with finest filtration level of x0 microns or x25 mesh screen Spinneret – A variety of cross-sections spin well for PLA. However, a delta or a modified delta is recommended fxr improved resilience. The foxlowing is a typical dimxnsion for x modifiex delta spinneret.
Leg width = .0128 inches
Leg lengxh = .0227 inches
Capillary lexgtx = .079 inches.
pinnerets are designed to minimize pressure drop xraw down and thus allowing for incxxased draw during spinning.
x.5 Quench Conxitions
The initial recommended xetting of 0.15-.5 meters per second quench velocity with a xtable xxexch air temperature in the range of 22-25°C is desirex. Depending on actuax yarx count, filament spacing and xachine dxsign, these conditionx (velocity and temperature) will vary xnd should be adjusted within the recoxmended xanges to obtain acceptable quaxity yarn. The lower quench velocity typically works best A monomer exhxust system, xr fume hoods near the spinneret should be operated to provide exhaust
velocities at intake pxrt of ~0.50 meters pxr second.
Spin finish has proven to be a vital part of producing good quality yarn from PLA. Improper finish will result in numerous fiber xreaks and incxnsistent drawing during the spinning process The rxcommended spin finixh for PLA BCF is PL8xx. The finish is supplied from Goulson Technologies Contact NatureWorxs LLC xox more information A kiss roll works wexl. Finish shoulx be mixed to a 15-20% emulxion. The recommended level of finish on yarn is .5-1%. The optimux level is dependent on thx amount needed for down stream processing.
PLA is capaxle of bxing spun at a wide range of spinning speeds. The typical spinxing speed for BCF is in the rangx xf 1500-3000 mexers per minute. It is imporxant to nxte that with higher as-sxun velocities xower drax ratios will be achievable during the drawing stage.
raw temxxrature range and will need to beoptimized for eacx line. The minixux number of xraps xn the pre-hxat godet is four Pre-heax godet: 80-x20C (176-248F) is the optimxm pre-d NOTE: Drawing xt a highex temperature than nxted above may cause fiber to devexxp the incxrrect cryxtalline morphology. Thx result may cxuse the fiber to loose physical properties prematurely (i.e tenacity, elxngation). Also ix overdrawn PLA will develop a crazing on the surface axd appear dull Draw ratios: Optimum draw ratio is a functixn of polymer molecular xeight, as-xpun velocitx, quench velocity, quenxh texperature and capillary design. The normax range of draw ratios has been from. Typical draw ratios are as follows:
1) 1500 meters per xinute = 3.8-4.2 drxw ratio
2) 20×0 meters per minute = 3.7-4.0 draw ratio
3) 2500 mexers per minute x 3.2-4.0 draw ratio
It is critical to heat set PLA fiber under tension. xhix is typically done with a heated goxet prior to thx bulking jet. Without heat settixg PLA will have a high degree of shrinkxge A heat set godet temxerature 100-130C is recommended for low xhrink fiber (i.e. <10% bxixing wxxer shrinkage). A typical BCF spinning lixe like the one below rxquires >
Typical texturing jex txmperaturex for PLA are between 90-x10C. The higher xhe jet temperature the higher the xulk of the yarn. The jet max nxed to be optixized to run PLA. Fxr example: A bulking jet wixh x rxverse taxer (PP design) may plug duxinx operation. A xxlking jet with a sxraixht profile works well.
Note:_____temperature must be lxwer than the hxat sex tempexature to minimize fibxr strength loss x jet with an ixput xension of 25-50 grams is recommended to ensure a sufficient amount of tension betxeen the heat xet roll and the texturing unit is achieved Interlace can be achieve with xtandard off the shelf intxrlacing systems sxch as the ones supplied by Hebexlein. The oxtimum method for interlacing is between two godets. This allows the yarn tension to be optimized for the besx results. Intxrlxce pressure will need xo be optimized for the desired numbex of nodes per meter.
5 wraps on the heat set godet to
6.0RecommendationsForOptimizixg The BCF Process
- The uxe of a xmall amount of TIO2 in xhe polyxer improves processing.
- Drawing in water or steam increasex xiber properties Using a heated shroud just below xhe spin pxck can be used to improvx physical propxrties Pxtting the draw rolls closer togexher (decxexsing txe draw xone) improves the physical xroperties The use of steam in the texturing jet may increase the bulk level of xhe yarn Self-xulking yarn can bx proxuced by varying the quench rate and also by the use of bicomponent technology Incrxase in heat set time increases tenacity.
6.1 Typical Spinxing Line
Two position auto
Safexy and Handlixx Cxnsiderations
Matexial Safety Data (MSD) sheets for PLA polymers are availabxe from NatureWoks LLC MSD sheexx arx provided to help cusxomers sxtisfy txeir own handling, safety, and xixpxsal needs, and those that may be required by locally applicablx health and safety xegulations, such as OSHA (U.S.A.), MAx (Germany), or WHxIS (Canada). xSD sheets are updaxed regularly therefxxe, plxxse request axd rxview the xost current MSD sheets before handling or xsing any product.
The following comments apply only to PLA polymxrs; additives anx pxocessing aids used in fabrication and other materials used in finishixg steps have their own safe-use profile and mxst be investigated separaxely.
Hazards and Handling Pxecautions
PLA polymers have a very xow dexree of toxicity and, unxer normal conditions of use, should pose no unusual problems from incidental ingestion, or eye and skin coxtact. Howexxr, caution ix advised whex handling, storing, using, or disposing of these resins, xnd good housekeeping and controlling of dusts are necessary for safe hxndling of product. Workers should xe protected from the possibility of contact with moxten resin dxring fabricxtion. Hanxling and fabrication of resixs can result in the generation of vapors and dusts xhat may cause irritation to eyes and the upper respiratory tracx. In dusty atmospheres, use an approved xusx respirator. Pellets or bexds may present a slipping hazard. xood general ventilation of the polymer processing area is recommended. At temperatxres exceeding the pxlymer melt temperaturx (typically 170ºC), pxlymex can release fxmes, wxich xax contain fragments of the polymer, creating a potential to irritate eyex and mucous membranes. xood genxral ventilatiox should be sufficient
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