IN THE PAST, synthetic alternatives to natural rubber gloves have triggered concerns about comfort and protection. But as new innovations, especially production techniques for synthetic rubber gloves have emerged, such concerns have also started to wane, writes Lyn Cacha in this report on the recently-held Latex & Synthetic Polymer Dispersions, in Kuala Lumpur, Malaysia.
Latex prices up, nitrile to benefit
To reduce operating costs and raise profit margins, some manufacturers are lessening their consumption of NR latex by producing thinner latex gloves (3.5 g) and stalling production expansions. A growing number of makers, meanwhile, are ramping production capacities for SR glove production. Emerging markets in Asia, Europe and Latin America will provide the next surge in SR glove demand over the long term given the low penetration rate of glove usage, large population base and improving hygiene standards.
Reviewing synthetic latices in available surgical gloves
However, SR gloves have their disadvantages. It has been reported that they are more likely to perforate, especially in arthroplasty, compared to latex gloves. In terms of the supply, output of SR nitrile gloves is maybe lower, depending on the product mix, since nitrile gloves take a longer time to cure.To help dispel concerns on SR glove’s unreliability, Kraton Innovation Centre Amsterdam conducted a study that systematically and quantitatively evaluated various types of commercially-available surgical gloves. The mechanical properties of four types of NR gloves, three types of anionic IR (AnIR) gloves, two types of ZN-IR gloves, and three types of polychloroprene gloves were tested. Mechanical properties measured include those related to protection (tensile strength, tear strength and puncture resistance) and comfort (small deformation, modulus at 500% elongation and hysteresis). According to Kraton’s Wouter de Jong, 12 different surgical gloves in size 7.5 were evaluated. The research team used the following testing instruments from the American Society for Testing and Materials (ASTM) – ASTM D3577 to determine the gloves’ thickness; ASTM D412 to measure tensile strength, different moduli and elongation at break; ASTM F1342 for puncture resistance; and ASTMD624 for measure tear strength. The ASTM requirements are mostly designed to guarantee sufficient protection of the surgeons and patients but not so much to ensure comfort during use.In terms of thickness, all gloves except for three types were within 200 micrometres. AnIR-B and ZN-IR-B were 250 micrometres, while CRL-A was about 175 micrometres. All gloves were thickest at the finger and thinnest at the cuff.
All the surgical gloves evaluated met the ASTM standard for surgical gloves. However, when the extensometer was used, tensile strength of NR gloves was below the specification for all NR samples. It turned out that the reason for the unexpectedly low figures for the NR gloves was in the use of the extensometer. Hence, NR seems to be susceptible to small disturbances when under stress.
The AnIR and CRL gloves suffer from easier tearing propagation than NR and ZN-IR gloves, but sustain higher or equivalent puncture energy, which may be related to tear initiation. Remarkably, the break pattern of the NR and ZN-IR was different than the pattern of the AnIR or the NYP types. The study showed that NR and ZN-IR types show an irregular break pattern, whereas the other types give a rather straight cut, perpendicular to the direction of the strain. The difference in break pattern for NR and ZN-IR can be an indication that their tearing behaviour is different than AnIR and CRL. The tearing propagation of the last two gloves may be faster. Overall, the study infers that all glove types studied offer comparable mechanical protection.
Improving barrier effectiveness with CHG coating Barrier effectiveness is vital in surgical gloves as it reduces the risk of contamination during contact with body fluids, mucous membranes or the damaged skin of patients. Mechanical stress, however, such as that occurring when gloves are repeatedly flexed through finger and hand manipulations, increase the chances of tears and punctures Taking protection a notch higher, a new antimicrobial technology has been developed by Ansell to provide added protection in case of an unnoticed glove breach during use. According to Eng Aik Hwee, Module Director, the technology uses an active ingredient, chlorhexidine gluconate (CHG), which reduces the microbial load on the active inside coated surface of the glove. About 4% of CHG, a water soluble and hygroscopic material, was coated in the inside surface.
In terms of comfort, a very thin layer of anti-stick overcoat was applied over the antimicrobial coating to prevent the glove’s inside surface from adhering to the skin and to facilitate easy donning. A panel of five evaluators tried the glove and evaluated it according to dry and damp-hand donnability, double gloving, blocking (glove-to-glove inside and outside and glove-to-packaging), and wet look. All of the evaluators rated the antimicrobial glove as very easy to use and with no blocking and wet-look.
For those allergic to protein, a test was conducted to find out if there were any traces of proteins on the antimicrobial glove. Results showed no detectable allergens and less than 50 water extractable proteins on the glove. It also indicated that the presence of antimicrobial agent has no correlation between the protein and allergen contents on the glove.
Tensile properties of the antimicrobial glove met the aged and un-aged requirements of EN455 standard. The retention of force at break value was found to be above 90% for the glove. However, the un-aged force at break value of the antimicrobial glove was found to be slightly lower than that of the control glove, probably due to the additional processing steps, for instance, the antimicrobial agent applied to the glove.
In vitro studies found that the glove killed more than 99% of an HCV surrogate virus and 99% of HIV-1 strain MN as early as 1 minute following exposure. The glove was also found to kill 99.7% to 99.9% of eight clinically relevant bacteria comprising gram-positive and negative and drug-resistant bacteria over 1 to 2 minutes exposure in similar studies.
The kill-rate of the glove samples was performed by spreading 0.1 ml of inoculums with 5% organic soil load in the glove fingers for a specific period of time followed by neutralisation with Butterfield’s phosphate buffer solution with product stabilisers (BBP++). Serial dilutions were then made and plated for counting. The log reductions from the initial microbial recovery levels were determined by comparing recoveries from the antimicrobial gloves with those from control gloves without antimicrobial agent.
Both real-time and accelerated aging studies confirmed that the glove has at least two years of shelf life in terms of meeting the EN-455-4 requirements. This was determined using the accelerated aging method. Within this period, the active ingredient remains stable and active.
According to Ansell, the application of CHG to a powder-free NR surgical glove did not affect the functional performance of the glove. All the tests results show that the antimicrobial-coated glove can help further reduce the risk.
Combining functionality and eco-friendliness with PUDs As gloves become stronger, they have also become tougher to dispose and recycle. With the increased use of rubber gloves worldwide, the quantity of used and waste gloves generated daily has become a problem. Awareness about environmental conservation has forced some glove manufacturing companies to look for eco-friendly solutions like polyurethane dispersions (PUDs) gloves. PUDs are a waterborne material that may bring a green image to the glove industry, as emphasised by Rolf Irnich of Bayer MaterialScience. With stricter regulations on carcinogenic mutation and reproductive substances for medical and food applications, waterborne PUDs may serve as an alternative solution.
The PUD glove manufacturing process goes through multiple steps
– clean mould, dry mould at 100°C, dry mould into coagulant, drying at 100°C for 1 minute, dry mould into PUD, leach in water at 45°C, curing at 130°C, cooling at 45°C, powder or dip into finish and drying and lastly, strip moulding at 100°C.
Once the gloves are ready, PUDs are applied by dipping the glove into a coagulant and then drying it at 100°C for 3 minutes. After drying, the glove is dipped again into a PUD paste and dried at 70°C to 90°C. The final stage involves leaching the glove into water RTP for 10 minutes and then drying at 70°C for 5 minutes.
According to the company, the dipping process enhances the gloves to be used in a wider dimension such as oil or chemical barrier as protection, better skin sanitation properties, waterproofing, non-conductive properties and improving tensile strength, which makes them reusable.
Compared to the traditional materials used to make disposable gloves such as latex, PVC and nitrile, PUDs offer a very simple formulation, easy processing and since they are made from a water-based polymer are much greener. Key elements that make PUDs suitable include resistance to water, chemicals and solvents; durability, varying degrees of flexibility and film hardness.
Present findings show that there is no concerned toxicity level coming from the conversion of polymer breakdown. More research is currently underway as the company hopes to make PUD gloves more breathable, allowing longer usage without build up of sweat leading to skin irritation. (PRA)
.