Analysis of PPE coverall properties with a view to COVID-19 protection
Abstract
- This is a hypothetical proposition based on the functional properties of PPE
- Some products and chemical agents’ commercial names are used only for example
- Subject to change incorporating further experiments
Objective
- To develop a suitable model for durable PPE
- To enhance its performance in terms of protection.
PPE – Personal Protective Equipment
Components – Gown, Mask, Hand gloves, Shoe cover, Goggles, Head shield
Fabric materials
For PPE coverall mainly two types of fabric are being widely used. Different combinations of fiber material and additional mechanical and chemical treatments increase the functional properties in terms of protection. Below is a glimpse on these fabric characteristics.
Option 1: Non-woven 70-90 GSM PE laminated fabric
(a) SMS fabric: Polypropylene pallets combination (spunbound +meltblown+ spunbound) makes SMS fabric. In case of better durability and heavier GSM requirement, SMMMS or SSMMS combination can be used. PE (polyethylene) or PTFE (poly-tetra-fluoro-ethylene) coating is applied to it for non-microporous lamination. This lamination can be non-breathable or breathable depending on its intended use. Higher protective layers of lamination, higher resistance to chemical permeability and fabric become non-breathable gradually with the increased weight of lamination film.
(b) BICO fabric: Bicomponent layers made from special fibers that have a polyester core and a polyethylene sheath. PE lamination film is applied to it for non-breathable functional properties. It is lightweight and offers better protection in case of high-risk exposure & sophisticated long-time wear. PPE made from this fabric is suggested for single use & disposable.
Option 2: Taffeta AgNP/PU coated 190T/210T/240T 60-80 GSM
It is mainly used for a raincoat, tent, bag, etc. However, fabric with finer count yarn, lower GSM, compact weaving with 1/1 plain construction to ensure less opening at warp-weft junction pores and obviously with other finishing treatment to make it waterproof & non-breathable can be used for PPE gown in case of less risk exposure.
Antistatic finish and AgNP (silver nano-particle) coating as anti-bacterial agents enhances its protective performance. The number indicated with T expresses fabric density. 210T means the total number of ends & picks per square inch is 210; so technically T=EPI+PPI. A higher number indicates more compactness in the fabric construction. Taffeta offers better durability against wash, so it can be reusable up to a certain limited extent.
Let’s take an example here from the product specification of the brand Orient intended for healthcare professionals. The fabric used in medical protective clothing is outer layer 30g breathable film + inner layer 30gPP nonwoven fabric (100% polypropylene) + 3g glue, 100% polypropylene, without fillers adhesives, and silicon.
The special coating treatment makes the surface smooth and repels inorganic liquids, effectively prevents chemical substances from splashing, and at the same time makes harmful ultra-fine solid dust difficult to adhere to.
Very few companies operate this type of highly innovative research. Some popular names are DU Pont, 3M (USA); Derekduck (Taiwan), etc. Different commercial models are developed for different purposes considering the protection levels of HAZMAT (hazardous materials) suit. For a biohazard like Covid-19 threat, Level C (USA standard) or Type 4-5 (EU standard) is a preferable category for PPE.
Hazmat Suit Product: DU Pont Tyvek®, Du Pont Tychem® 10000, 3M-4565, Ultitec3000T, etc.
3M-4565 protective suit: It is a level C (USA standard) or Type 4,5 (EU standard) product. Non-micro-porous PE laminated BICO fabric; single-use and disposable, a three-panel hood, anti-static, taped seam, elasticized waist ankle cuff.
Tychem® 10000 coverall: It’s a level B suit designed for chemical hazards mainly. The garment shall be constructed of DuPont™ Tychem® 10000 — a patented fabric consisting of multi-layer barrier films laminated to both sides of a 4.0 oz/yd2 polyester substrate. Respirator Fit Hood; elastic wrists; attached socks with outer boot flaps; double storm flap with an adhesive closure; taped seams.
Properties, special features and process hints
Liquid resistant and breathability comfort: Fabric must be water-resistant; it needs a durable waterproof finish. Outer layer surface can be waterproof treated with FEPM/ PE/ PU/ PVC/ PTFE etc. hydrophobic laminated coating while inner surface should be water repellent. But this finish will reduce the breathability of the fabric and cause discomfort due to the perspiration problem. So additional mechanism needs to be addressed at the inner surface to minimize the droplets of perspiration.
To rectify this problem a three-skin model can be suggested as a safer option. Here the PPE gown is a double layer inclined by stitch; the outer layer is waterproof that provides protection; mid-layer as a lining is water repellent which acts like an additional barrier to the innermost gown.
PHOBOL® Extender SFB, ZELAN™R3 (Huntsman), Ecorepel® (Schoeller Textiles), etc. are some commercial product names for finishing agents that offer water repellence at various degree of level for different types of fabric.
The innermost gown is separately worn; a thin breathable micro-porous nonwoven similar to surgical gown but specially treated with alginate & hydrophilic agent ULTRAPHIL® for distinct fluid management. This layer will absorb moisture to reduce discomfort from body perspiration.
Anti-static finish: Anti-static properties develops as a subsidy of water repellent finish. It also depends on material properties. Furthermore, chemical treatment is required for enhanced level performance. Some commercial examples of antistatic agents- ZEROSTAT® (Huntsman), CIRRASOL PP118 (Croda) etc.
Anti-microbial finish: Alginate & Chitosan coating (natural biopolymers) can be used on inner gown fabric for absorbency and odor control. Silane coating (SiH4 & its derivatives group) is applied by the pad-dry-cure method to impart antimicrobial properties on the outer fabric. Again, the fluoropolymers coating is applied to impart blood repellence characteristics. Electrochemical treatment of silver nanoparticles (AgNP*) activated with ZnO also enhances antimicrobial properties.
Example: Ultra-fresh Nm-100, Dm-50 or XQ-32; Bio shield AM 500, etc. [3- (trimethoxy silyl)- propyl – dimethyl octadecyl ammonium chloride] is applied to polypropylene or cotton fabrics by a cold pad-batch method in the presence of an alkaline catalyst to evaluate its use as a durable antimicrobial finish.
Seam-sealed: Less seam, less risk of openings; pattern design should avoid seam line as much as possible. For medical garments basic seams are used- 3 thread overlock serged seam, blind stitch bound seam inside especially at crotch area; some cases might require lapped seam with stitch class-504 depending on the function.
Most importantly waterproof, antibacterial, washable, fluorocarbon/PU coated heat-seal tape (made of similar body material) should be applied on a seam line at 200C by ultrasonic hot air seam sealing welding m/c to prevent leakage.
Example (brand-orient): Medical protective clothing needle thread is stitched and glued. The stitch pitch is 8 needles to 14 needles per 3cm. The stitches are even and straight. Double sealing rubber strips (PP) are added to ensure the tightness of medical protective clothing.
Elastic closure at hood, sleeve, or leg hem: Neoprene rubber elastic is used at several functional areas. Elasticised hood makes smaller face opening but flexible to facilitate other complementary instruments, fully elasticized waist to retain the shape while quick body movement, elasticized sleeve & ankle need enough gathering & folds to keep it tightly enclosed.
Example: ( brand-Ultitec): offers extra chinstrap, zipper fastens to the underside of the chin, ample crotch, elasticized wrist with finger loop
Waterproof airtight zip closure & cover flap: Front opening with waterproof airtight zipper (PROSEAL®), reversed zip one end closed is a better option, attached by welding or sealed seam. The double-layer storm flap is a must to cover zip; flap can be closed with Velcro adhesive.
Reusable: This is the most challenging requirement for developing a reusable PPE coverall while it’s about retaining properties after several washes care and alcoholic disinfectant application. Washing actually degrades the product performance gradually. In general, single-use disposable PPE are safe; especially when used against a high spreading contact threat like coronavirus. Proper donning & doffing method & regular disinfectant care must need to follow accordingly.
Care instruction depends on the final product properties. Nevertheless, in a constraint of limited stock, a few washes can be supported. Use disinfectants carefully, wash with hot water, detergents can be used, better not to use dry clean agents, no heat press iron, dry in hot sunlight.
For reusable properties, high GSM laminated SMMMS or SSMMS nonwoven fabric with additional durable finishes can be workable. A three-skin model will provide better durability & safety measure.
Other components of PPE are better to be disposable and single-use for a doctor/nurse/technologist in every 6-8 hours shift duty.
These should be externally fitted (not inclusive with gown) for easy disposable purposes. A brief note are pointed below for each:
Mask: N95/KN95/FFP/Surgical mask- (depends on work risk). Respiratory apparatus with external oxygen supply is not recommended by WHO if not potentially high-risk involvement.
Gloves: Two pair hand gloves; inner latex/vinyl gloves, outside nitrile gloves; cuff length should reach mid-forearm.
Shoe Cover: PVC sole antiskid, PE laminated body, elasticized closure at top.
Goggles: Safety cover goggles for eye protection, splash-proof, properly fitted non-ventilated types.
Head shield: Protection from flying particles, transparent plastic, less thickness, easily disposable.
Others: It’s better to use bouffant cap & a moisture absorbent thin gown inside for extra protection & comfort.
Arranging the quick supply of disposable PPE always ready in a massive range quantity is nearly an impossible task. Such a high technically enriched product is obviously costly; so, each day a new full set of PPE for each person is neither affordable nor manageable in supply v/s demand quantity.
Reusable PPE is a growing demand in the market for the upcoming days ahead. It’s time for investment in hi-tech product manufacturing in the country itself, rather than being dependent on imported items. Healthcare industries need to be promoted for more research and innovation on protective suits. It’s a global need; a worth preparation for upcoming threats; a promising scope for investment in scientific research.
References:
Preferred product characteristics for personal protective equipment for the health worker on the frontline responding to viral hemorrhagic fevers in tropical climates- World Health Organization
Guidelines for personal protective equipment (PPE)- Environmental Health & Safety- University of Washington
3M- safety products catalog // 3M-Technical Bulletin
polymerdatabase.com
Performance-enhancement finishes for nonwoven fabrics- Dr. Naresh M Saref, Dr. Sanket P Valia 28 February 2017
biological and chemical protective finishes for textile– U. Turaga, S. Ramkumar, in Functional Finishes for Textiles, 2015
Seams for protective clothing–an overview- Shanthi Radhakrishnan and Devendra Kumari- World Journal of Textile Engineering and Technology, 2017, 3, 16-23
Improving body movement comfort in apparel– S.P. Ashdown, in Improving Comfort in Clothing, 2011// factors Affecting Comfort: Human Physiology And The Role Of Clothing– A.K. Roy Choudhury, C. Datta, in Improving Comfort in Clothing, 2011
