TECHNOLOGY CLEANROOM www.cleanroom-technology.co.uk December 2012 THE INTERNATIONAL JOURNAL OF CONTAMINATION CONTROL SELECTING WIPES WITH MAXIMUM PICK-UP POWER ● Go West to minimise particulates from packaging components ● Assessing membrane filters for sterile liquids ● Making a difference to lab performance – the S-Lab Awards SELECTING WIPES WITH MAXIMUM PICK-UP POWER Go West to minimise particulates from packaging components Assessing membrane filters for sterile liquids Making a difference to lab performance – the S-Lab Awards
Transcript
T E C H N O L O G YCLEANROOM
www.cleanroom-technology.co.uk
December 2012
THE INTERNATIONAL JOURNAL OF CONTAMINATION CONTROL
SELECTING WIPESWITH MAXIMUMPICK-UP POWER● Go West to minimise particulates
from packaging components● Assessing membrane filters
for sterile liquids● Making a difference to lab
performance – the S-Lab Awards
SELECTING WIPESWITH MAXIMUMPICK-UP POWER
Go West to minimise particulates from packaging componentsAssessing membrane filters for sterile liquidsMaking a difference to lab performance – the S-Lab Awards
CLEANROOM TECHNOLOGY December 2012 www.cleanroom-technology.co.uk
Microfibre has a high sorptive capacityaround 6 to 8 times its own weight in water.The fast wicking ability means a wipe canremove spills quickly and easily, so it is verysuitable for mop to dry situations.
However, there are some downsides tomicrofibre in cleanroom environments: thefibres are less durable and also create muchhigher levels of fine particle contamination.The microfibre would need to be launderedto reduce these levels of contamination.
Furthermore, microfibre is high in cost sonot ideally suited to being a single usematerial. It is most relevant to applicationswhere mop or wipe to dry performance isparamount and the activity of continualrelaundering does not create problems. Asplit microfibre containing nylon is notcompatible with bleach-based disinfectants.
Risks of relaundering Table 1 shows a comparison of differentblends of microfibre vs 100% polyester andtheir corresponding attributes. In many casesthe high initial cost of microfibre is balancedby relaundering and, where relevant, theresterilisation of the mop or wipe. Mops,especially, are laundered and reused.
Microfibre picks up and holds particles better thancotton, but has drawbacks of its own. KarenRossington discusses the pros and cons ofvarious fibre types used for cleanroom wipes
the differenceSplitting
C leanroom wipes have their origins inthe nuclear industry when the firstcritical wipes were cotton twill used to
control radioactive particles from leavingnuclear reactor containment. The emergenceof microelectronic manufacturing requiredcleaner wipe options and cotton twill wasreplaced by nylon monofilament. By the mid1980s polyester monofilament became thestandard critical environment wipe.
Today cleanroom wipes for all types ofcritical environment are big business. Asmanufacturing technology innovated so thedemand for even cleaner wipes increased.
In 1998 Contec introduced the firstpresaturated wipes for cleanrooms to reducesolvent consumption and increaseconvenience. One of the quickest adopterswas the medical device industry, which sawthe productivity improvements and processcontrols that the technology offered. Sterilepresaturated wipes were introduced in 1990for the pharmaceutical industry and thedeveloping biotech market.
In the late 1980s microfibre wasintroduced. The definition of a microfibre isa fibre with less than 1 decitex per filament,where a decitex is a measure of linear densitycommonly used to describe the size of afilament or fibre.1 One decitex is 9/10 of adenier. The fibres can be combined to createyarn, which can be then be knitted or woveninto a variety of constructions.
There are two main types of microfibrefabrics: splitable and straight filament.Straight filament microfibres tend to bemade from 100% polyester. Splitablemicrofibre consists of very fine threads ofpolyester and polyamide (nylon) combinedto form a single thread. The nylon is used toglue the fibres together until they are splitlater in the process.
Rather than the rounded threads found inother yarns, split microfibre has numerouswedges that provide the ability to collectmicroscopic particles from a surface (seeFigure 1). This expanded surface area and thecapillary action of the fine threadsdramatically increase a microfibre wipe’ssorbancy.
This split structure gives the wipe theability to pick up particles even when dry,and can easily remove residues, oftenwithout solvent. The split fibres createmicroscopic “hooks” that collect and holddust, dirt and particles more effectively thanrounded fibres such as cotton (see Figure 2).They are also positively charged so attractelectrostatically the negatively charged dirt.
Virgin wipes are very soft so they won’tdamage surfaces; however, care should betaken when reusing wipes as the verystructure that makes them so good at pickingup particles also means that particles getstuck in the fibres which can then scratch asensitive surface.
However in a cleanroom environment thisis not without risk. Microfibre can be easilydamaged by heat or harsh chemicals; thiscan lead to a mop or wipe degrading overtime, affecting both the cleaning ability andthe sorbent capacity of the mop.
As cleaning is carried out from thecleanest to the dirtiest area within acleanroom complex, the soil load on mopscan be significantly different. It is not easy forthe laundry to guarantee getting all the mopsback to the same level of cleanliness everytime. A question that must be asked of thelaundry is what other products your mopsare washed with. Mops and wipes often donot make up enough volume for a full washload and so laundries will often combinemops and wipes into one washload. This canlead to cross-contamination, which canleave particles or other contaminantstrapped in the microfibre product andreturned to the critical environment.
The drive for a product that could providethe benefits of microfibre while minimisingthe downsides led to the introduction of thefirst new category of wipe in almost 30 years.MicroGenesis, by Contec, combines the bestfeatures of knitted, nonwoven, and
www.cleanroom-technology.co.uk December 2012 CLEANROOM TECHNOLOGY
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redistribution, and with a jar containing onlyclean DI water and wipe to determine theamount of particles released from the wipe.
The definition of particle capture andrelease in this experiment was as follows:
The total number of particles that weregenerated = the initial number of particles inthe suspension, the number of particlesreleased from the wipe during biaxialshaking, and the number of particles createdfrom the break-up of larger aggregates. If thenumber of particles captured is negative,meaning that more particles were releasedinto the water than removed, then thenumber of particles captured is defined aszero.
The number of particles captured by thewipe = initial particles in solution + particlesreleased from wipe + particles created fromparticle break-up minus particles afterbiaxial shake.
microfibre technologies to deliverunprecedented performance to criticalwiping applications.
The MicroGenesis wipe has a micro-terrypile to give the fast and efficient pick-up andretention of particles for which microfibre isknown. However, the wipe uses 100% poly-ester microfibre yarn knitted into a thermallybonded polypropylene substrate; this limitsthe amount of microfibre required andmakes the wipe more suitable for single use.
This structure applies microfibre only tothe wiping surface where it is needed whilesealing the base of each stitch in a thermallybonded base. This more cost-effectivestructure still delivers the required amount ofmicrofibre to pick up and retain microscopicparticles, dust and light oils from criticalenvironments.
There are other developments that canprovide a wipe with exceptional pick-up andretention of particle properties without theuse of microfibre. All fabrics can be treated toimprove their performance. One patentedtreatment by Anticon that permanentlybonds to the fabric traps 35 times moreparticles than an untreated wipe and retains95% of the particles that are trapped.Interestingly, this performance is enhancedrather than degraded in the presence ofalcohol or solvent.
The IEST test methods for testing wipes,determine how many particle and fibres awipe releases but there is no standard testmethod to show how many particles a wipepicks up. To prove that the wipe was trulyachieving this level of particulate pick-up,Peter K. Kang and David Hildreth developeda new robust test method.2 In general thetesting process was very similar to IEST-RP-
CC-004.2 sec 5.2 in that it used the samespecified shaker, same duration of shakingtime and laser particle counter.
In the test two different types of standardtest dust were used – A C Fine Test Dust andCarbon Black Particles. Suspensions of bothparticles were made up in deionised (DI)water. An ultrasonic bath was used to ensurethe particle aggregates were broken up asmuch as possible. The particle concentrationof the suspension was measured and then aweighed dry wipe was added. Thesuspension was shaken for 5 minutes on abiaxial shaker.
The wipe was then removed and added toa jar containing clean DI water where theparticle count had already been measured.The weight of the wet wipe was recorded andthe jar with the wipe in it was shaken on thebiaxial shaker for 5 minutes. The wipe wasthen removed and discarded. The particleconcentration in both jars was recorded.
This procedure was repeated with a jarcontaining only particle suspension todetermine the amount of particle break up or
Figure 1: Electron micrograph ofmicrofibre showing the wedge-shapedrather than rounded ends
Table 1: Comparison of different microfibre blends and their corresponding attributes
Conversely, if the number of particlesreleased is negative, then it is defined as zerosince no particles were released: number ofparticles released = particles after biaxialshake minus particles in wet wiper minusparticles released from clean wipe.
For purposes of the tests, “small” particleswere defined as the sum of 0.5µm or largerparticles and “large” particles were definedas the sum of 5.0µm and larger particles.Initial concentrations for small particles andlarge particles were approximately 3,000,000and 10,000 particles respectively.
The test results for A.C. Fine Test Dustsshowed treated wipes captured over threetimes more small particles than traditionalwipes, releasing only 14% of the particlesthey captured. Additionally, they capturedover 35 times more large particles than theother wipes tested. Only a very small per-centage of captured particles were released.
Test results for small and large carbonblack particles showed that treated wipescaptured 4 times more small particles and7.5 times more large particles than the otherwipes tested. The treated wipes released 2%of the captured small particles and in thelarge particles tests treated wipes released3% of the captured particles.
For both particle sizes the treated wipeboth captured and retained significantlymore particles than an untreated wipe.
To paraphrase Peter Kang, cleanroomwipes need to arrive clean and leave dirty.The ideal product performance for acleanroom wipe is that it does not add to thecontamination while performing theremoval of particles, spills, biofilms or dirt.Various innovations in both wipe substratesand wipe treatment have aided in this,creating wipes that are ideal at not onlypicking up particles but retaining them untilthe wipe is removed from the cleanroom.
The test methodology outlined by Kangand Hildreth gives a way of comparing wipesagainst these parameters of capture andrelease. Alternative ways of blending
microfibres have allowed the creation ofwipes with microfibre properties at the costof a disposable wipe. CT
References1. Textile Terms and Definitions, 11th Edition, The TextileInstitute2. Testing Wipers for Particle Retention and Attraction,Controlled Environments Peter K Kang PhD David Hildreth Management – Vocabulary – Guidelines for use in standards
Figure 2: Schematic showing how split fibres (left) create microscopic “hooks” whichcollect and hold dust, dirt and particles in contrast to rounded fibres (right)
CONTACTKaren Rossington is a marketing consultantfor Contec Inc● [email protected]● www.contecinc.com
Microfibre Cotton
CLEANROOM TECHNOLOGY December 2012 www.cleanroom-technology.co.uk
SIMPLE SOLUTIONS FORCOMPLEX PROBLEMS
Contec’s mopping systems are ideal for many disinfecting and cleaning tasks in critical life science and microelectronics environments. Apply disinfectants and cleaning solutions to floors, walls and ceilings with Contec’s VertiKlean, VertiKlean MAX, EasyCurve or Edgeless mops. For isolators, LAF hoods and work benches, choose our EasyReach Cleaning Tool.
Many of our cleanroom mops are available validated sterile for use in aseptic areas. We offer stainless steel and autoclavable polypropylene buckets and carts to complement each of our mops and wall washing systems. Stainless steel and anodized aluminum mop handles in several styles and lengths are available.
SIMPLE SOLUTIONS FORCOMPLEX PROBLEMS
Contec, Inc. manufactures sterile and non-sterile cleanroom wipes, mops and cleaning systems for critical cleaning. Visit www.contecinc.com for more information. To request an
evaluation sample phone/fax 0845 652 2582 or email [email protected].
