How then does the customer understand the cleanroom wiper data presented and the degree of comparability between data presented by cleanroom wiper manufacturers?
Let’s begin with a basic primer on the critical wiper data reported by most cleanroom wiper manufacturers in product data/information sheets:
Basis Weight is the actual material weight of the product and is generally reported in the format of g/m². The determination of basis weight is a simple technique and therefore should be comparable among different product data/information sheets.
Sorbency, sometimes referred to as absorbency, is related to the amount of solution a wiping material can take up either through absorption or adsorption. Absorption is typically related to naturally hydrophilic materials, such as cellulose non-wovens, while adsorption typically relates to synthetic materials, such as polyester knits, which without treatment are hydrophobic. Sorbency is measured in terms of capacity, efficiency, and rate with fairly straightforward calculations which should be comparable among different product data/information sheets:
Capacity is the term typically used to express the total volume of liquid that can be held by a wiper and is expressed as cc/m² or mL/m². Other terms used include absorbency and extrinsic sorbency.
Efficiency is related to how effective the material is at absorbing or adsorbing a liquid and is expressed as cc/g or mL/g. Other terms used are specific absorbency or intrinsic sorbency.
Rate is related to how fast a water drop’s specular reflection can disappear after dropped onto a wiper surface and is expressed in seconds. Other terms used are time to ½ and time to sorption.
Non-Volatile Residues are the unspecified extractable matter that can be extracted from a wiper under a certain set of circumstances related to time, temperature, and solution and is generally reported as % by weight or g/m². Other commonly used terms are NVRs and extractables. Typically non-volatile residues are extracted in DI water and in IPA. Other solutions, such as Acetone, may be used based on customer requirements or process. There are two basic methods for performing the extractions:
1. The first method exhaustively extracts all non-volatile matter using boiling solvent.
2. The second method is a short-term or ambient temperature extraction that more closely relates to how actual wipers are used in most processes.
Most wiper manufacturers typically report short term or ambient temperature extraction data; however, some do report using the full exhaustion method.
Ions are the quantified species of matter that can be extracted from a wiper and are generally expressed as ppm or ppb. While the extraction method could use elevated temperature most, if not all, wiper manufacturers use an ambient temperature soak for the extraction. Most, if not all, wiper manufacturers also utilize Ion Chromatography (IC) to measure the extracted ion content. Due to the consistency in technique and measurement equipment, ionic content is typically comparable among competitor product data/information sheets.
Fibers and Particles state the amount of burden released from a wiper under a given set of conditions and are composed of releasable particles, those present on a wipers surface, and generated particles, those that are created by exposing the wiper to mechanical energy. The typical data reported is for fibers and particles released under mechanical energy and generally expressed as fibers and particles/cm2 or fibers and particles/ m2. Fibers and particles can also be reported in different size ranges. Typically fibers are reported in the 100 µm size. Particles are typically reported in the 0.5 µm size; however, other sizes such as 0.3 µm and 5.0 µm may also be reported.
There are three main methods that can be used in fiber and particle testing: zero stress, orbital shake, and biaxial shake. Zero stress measures readily releasable fibers and particles with no mechanical energy applied. Orbital shake is used to impart moderate mechanical energy to the surface of the wiper at 150 rpm (rotations per minute). Biaxial shake is used to impart vigorous mechanical energy to the surface of the wiper at approximately 280 opm (oscillations per minute). Both the orbital and biaxial shake methods produce a combination of readily releasable and generated fibers and particles. As part of the testing methodology, wipers are immersed in either a 100% DI water solution or a surfactant/ DI water solution. Fibers and particles are typically measured by LPC (Liquid Particles Counter) with SEM (Scanning Electron Microscopy) used as an alternate method. Due to the multiple combinations allowed within the particle and fiber testing methodologies for shake equipment, immersion solutions, and analytical measurement devices, trying to compare fiber and particle data presented on product data/information sheets is most often not an apples to apples comparison and should only be used with caution and a complete understanding of the exact differences in the product test methods.
From: Understanding Cleanroom Wiper Test Data and The Role of Product Data/Information Sheets