What is nitrile rubber ? What are so-called “ soft “ nitrile gloves ?
The full and proper technical name is acrylonitrile - butadiene rubber ( NBR ) which is mainly a random co-polymer of acrylonitrile monomer units ( the minor “ plastic “ component ) and butadiene monomer units ( the major “ rubbery “ component ) . NBR as a commercial polymer can be supplied with different composition by weight of the acrylonitrile, varying from about 25 % ( low ) , 30 % ( medium ) to 40 % ( high ) depending on the properties required and the intended applications . Basically as the plastic and somewhat polar acrylonitrile component is increased and the rubbery , non-polar butadiene component reduced , the overall rubber material becomes less elastic and stiffer but stronger with better overall resistance to solvents and chemicals . Medical gloves need to be as soft , flexible and elastic as possible during their intended usage for the examination of patients and diagnosis of diseases .
Even though “ low “ acrylonitrile content NBR has to be used , we can see that the resulting nitrile glove product , because of its reduced rubbery component , will never have the desirable features of softness, flexibility and elasticity as found inherently in a glove made out of natural rubber ( NR ) which has a 100 % rubbery component of isoprene repeat units . In actual practice , the NBR latex that is used for gloves making by the dipping process is further necessarily carboxylated with about 5 % of another plastic , polar methacrylic acid component at the expense of the rubbery butadiene component which further compromises and adversely affects these desirable features of the nitrile gloves so made . Nevertheless , for any given carboxylated NBR latex , by using a suitable combination of compound formulation with appropriate manufacturing process parameters , these desirable
features of softness , flexibility and elasticity in the resulting gloves can be optimised and improved considerably to be closer to those of NR gloves . By further reducing the glove weight
or thickness to below 4 mil , these ‘’ soft “ nitrile gloves are now the practical and cost effective solution in the search for an examination glove that is totally free of latex protein and its related Type I allergy which are always an issue of concern associated with the use of NR gloves .
What are tensile properties and stress - strain curves ? What is stress retention ? How do you read , interpret and use them to help reveal more about the characteristics of a glove (typically nitrile ) being tested and its expected behaviour or performance in actual service ?
One of the most commonly used methods for testing of material strength of a rubber product is by tensile testing which involves pulling a test sample of the product under tension at a slow constant rate until it breaks or ruptures . During this test , both the load applied and corresponding extension of the rubber test piece are monitored and recorded continuously. Tensile stress or modulus ( M ) refers to load per unit cross sectional area of test piece and the strain is the elongation that it produces , commonly expressed as % increase in its original length . A plot of this then gives the stress – strain curve . The stress at break or rupture is known as tensile strength ( TS ) while the corresponding strain is the elongation at break ( EB ) . When talking about tensile properties , it is common and necessary to quote and list down not just TS and EB but also the interim modulus at odd elongations 100 % , 300 % , 500 % etc until break . This is because all these have to be read together ( ie shape of the stress- strain curve ) in addition to another property called stress retention in order to get an overall idea of the characteristics and behaviour or performance of the rubber product . Stress retention is an indication of rubber elasticity and in the case of a rubber glove , its ability to retain its shape to give a snug , good fit during prolonged usage . The standard method of measurement is to determine its SR 300 or % of initial stress applied that is retained after 6 minutes at 300 % elongation .
The “ softness “ of a rubber glove when donned and put to use is indicated by low modulus ( stress ) values at low elongations typically up to 300 % ( M300 ) but this must be accompanied by good “ strength “ as indicated by a rapid increase in modulus values nearer to break point culminating in medium high TS and moderate EB . This is the ideal “ soft and strong “ glove as opposed to a “soft but weak gummy “ glove if its EB is excessively long and modulus values do not pick up rapidly and sharply eventually . Conversely , even if a glove has very high TS but low EB and high M300 , it will be “ strong but hard “ . For its material type , a “ good “ nitrile examination glove that is soft , strong and elastic would have typical values of
M300 : 3.0 - 4.0 MPa , M500 : 10.0 - 12.0 MPa , TS : ~ 20 MPa , EB : 580 - 600 % , SR300 : 35 - 40 % jointly . A high stress retention or elasticity is an indication of good and correct type of curing in the glove which would further improve its durability and resistance to chemicals and solvents in general .
How do you build-in all the desirable features of feel ( tactility ) , fit , comfort and durability into your nitrile gloves ?
The main pre-requisite for all of the above is the attainment of the correct and appropriate material property , as explained above , through a special formulation and carefully controlled process during the manufacturing of our nitrile gloves . The “ soft “ and elastic nature of our nitrile gloves provide optimal dexterity and flexibility when they are donned in use . And , in addition , because of its sufficient material strength , our gloves can be made thinner with thickness down to 3.5 or 4.0 mil which further enhances their dexterity and flexibility . The feel or tactile sensitivity of glove is also enhanced by this reduction in thickness especially at the finger and finger tips which is made possible by our gloves having uniform thickness from cuff to finger tips in order that the cuff area does not end up excessively thin and weak . The smooth finish on the outer working side of our gloves also allows maximum surface area contact and ‘’ feel “ with external objects or surfaces . Our gloves provide good fit and allow maximum movement of fingers and hand without constricting and causing discomfort to the hands . This is made possible by good formers design through all the sizes with respect to dimensions of palm width and all the fingers ( shape , length , circumference , their relative positions ) . Over the some 20 odd years of our manufacturing existence , together with customers feedbacks , the dimensions of our custom made formers have been revised from time to time so as to produce gloves that fit the average users’ hands better with minimal constriction and discomfort . The “ softness “ of our gloves with “ low “ M300 values will further ensure that gloves , even if somewhat tight fitting , will not be too stiff to cause hands fatigue easily . There is a further shrinkage of gloves ( up to about 5 % ) made from formers and careful control of compound formulation and main cure conditions are practiced to control this for each type of product so as to finally ensure the correct sizing and fit through all the sizes .
How do your powder free nitrile gloves allow for maximum gripping abilities , both dry and wet ?
This refers to the finishing on the outer gloves working side , which is actually the inner side in contact with formers during the manufacturing process . Our gloves have excellent grip both dry and wet that will not change or deteriorate over time because of our unique way of rendering this surface powder free online during the manufacturing process . A physical process is used here whereby this glove surface is coated with a thin film of inert polymer to remove the inherent rubber stickiness . This polymer treated outer surface , though non-sticky , has a high coefficient of friction with any objects and materials dry or wet thus allowing for their secure grasping and gripping . In contrast , the traditional way of making powder free gloves by chlorination offline has the difficulty in controlling the extent of chlorination , which is a chemical reaction that continues slowly over time , and hence smoothness of gripping surface . On top of this chlorinated rubber surface has a particularly low coefficient of friction with wet surfaces .
Why do yellowish to brownish stains appear on some rubber gloves surfaces especially after using ?
This is called copper staining which is as a result of the formation of the coloured copper dithiocarbamate complex from the reaction of copper with the residual accelerators , specifically the zinc dialkyl dithiocarbamates class , used in the making of these gloves . These yellowish - brownish patches , though unsightly , are just aesthetic in nature and do not adversely affect the functionality of the gloves in any way . Traces of copper are typically present in unwashed hands that have been in contact with coins , keys and other copper containing articles or objects . Needless to say , if hands are washed clean before donning gloves , this phenomenon will not happen .
What products ( eg chemicals , creams , lotions etc ) can or cannot be used in conjunction with your nitrile gloves ?
Nitrile rubber by itself is slightly polar in nature and therefore , in general , has excellent chemical resistance against non-polar hydrocarbons solvents , oils , greases but poor against polar chemicals and solvents ( eg ketones , ethers and esters ) . For instance under the EN 374-3 : 2003 standard for testing of resistance to chemicals , nitrile rubber gloves perform well against non- polar hydrocarbon solvents like hexane , heptanes and alkalis like sodium hydroxide but poor against polar chemicals like methanol , acetone , acetonitrile , dichloromethane , carbon disulphide , toluene , ethyl acetate , 98 % sulphuric acid . For permeation testing against chemotherapy drugs under the ASTM D 6978-05 standard , our 3.5 mil nitrile gloves showed chemical breakthrough time of 15 minutes for Carmustine and 30 minutes for Thiotepa respectively but no such breakthrough was detected even after 240 minutes for all the other drugs tested .
What are the optimal storage conditions for your gloves ?
Our products are best stored as fully packed inside dispensers and cartons , unopened , in a cool , dark place ( away from direct sunlight and fluorescent lightings ) . Stored in this way , our products have been shown under an accelerated aging study to have excellent resistance to aging and degradation with their effectiveness remaining intact well in excess of 10 years . A real time stability study of up to 5 years , which is the maximum shelf life that can be claimed officially , was successfully carried out under this condition to support this accelerated aging study .
Are there any precautions one should be aware of when using your nitrile gloves ?
a) Keep unopened cartons in a cool , dark place .
b) When using gloves from dispenser , keep box with remaining gloves inside away from heat , direct sunlight , UV or fluorescent lights .
c) Disposable , single use only .
d) Reduced durability if handling polar chemicals and solvents . Under such circumstances , glove change after 5 to 10 minutes continuous use is recommended .
What are the challenges in nitrile examination gloves production for your group going forward ?
a) More cost competitive through increased productivity and efficiency - higher output and improved quality leading to automatic direct strip and pack with reduced inspections .
b) Further glove weight reduction - thinner and lighter gloves ( M size < 3.0 gm ) . More uniform thickness ( to avoid too thin cuff ) with improved strength and durability of gloves .
c) Develop and further enhance following glove features :
---- softer , stronger , more elastic and comfortable like NR gloves
---- “ chemically clean or cleaner “ gloves with much reduced or no chemical residues remaining . Apart from meeting all international medical and food regulations , they will have even lower or no risks of skin irritation , sensitisation and Type IV chemical allergy . Meeting additional and more stringent biocompatibility tests like low nitrosamines and nitrosatable amines residues together with low cell cytotoxicity would represent major breakthroughs.