Natural Rubber Latex Products Research Articles

Unleashing excellent antibacterial performance of natural rubber composites via herbal extracts

Natural rubber latex (NRL)-based products often suffer from poor antibacterial performance, which limits their applications. Here, we fabricate NRL-based materials with enhanced antibacterial properties by incorporating natural plant extracts. Chinese herbal extracts/NRL compounds are prepared by compounding the relevant antibacterial natural plant extracts with the NRL, and the resulting mechanical properties and thermal stability are investigated. Mugwort/NRL and honeysuckle/NRL show the best antimicrobial effect, destroying the cell structure of various bacteria; no complete bacterial cells were found in the antimicrobial area. The excellent antibacterial properties，good cell compatibility and well-retained mechanical performance of the fabricated materials validate the proposed method as a novel, easy approach to preparing antibacterial NRL products. When the content of Chinese herbal extracts was 7.5 wt%, the Chinese herbal extracts/NR composites exhibited the best antibacterial and comprehensive mechanical properties. These products can be used in medical applications such as condoms, medical gloves, medical catheters and broaden the application of traditional Chinese herbal medicine. More importantly, the “template method” is proposed to rapidly determine the antibacterial ability of composite latex. This method can be applied to further scientific research and facilitate industrial production, providing strong technical support for developing more antibacterial latex products.

Durable and Nontoxic Natural Rubber-Based Composites with Antibacterial Properties.

Natural rubber latex (NRL) has prophylactic properties and is used to make pathogen-isolating products like condoms and surgical gloves. However, obtaining NRL and casting it into durable products are challenging. Consequently, progress in the research and development of medical NRL products has been slow. This study aims to strengthen NR and induce it with bactericidal properties. In this regard, we introduce inorganic whiskers into the NRL and synthesize whiskers/NR composites with strong mechanical and antibacterial properties. The method proposed herein is a template method, which can rapidly and efficiently reveal the antibacterial effect of the composite latex, providing convenience for research institutions and factories studying antibacterial latex. A complete system is established for studying the antibacterial medical NRL, and a precedent is set for the relevant products.

Preparation and properties of NR/EUG composite film

Natural rubber latex (NRL) products have the following problems: poor dimensional stability caused by low modulus and difficulty in wearing caused by high surface adhesion. In order to solve the above problems, the present paper developed eucommia ulmodies latex (EUL), and successfully prepared natural rubber (NR)/ Eucommia ulmoides gum (EUG) composite film by blending EUL into NRL. The results showed that the appearance of EUL was milky white, which was similar to natural latex. The latex particles were regular spherical, and the particle sizes were in the range of 100 nm~2000 nm. Like the solid EUG, the EUG in latex particles kept crystalline state as well, which were α-form and β-form respectively. As the content of EUG increased from 0 % to 40 %, the crystallinity of the NR/EUG composite film gradually increased, which increased the highest modulus by 207 % and enhanced the dimensional stability of the film. At the same time, the crystallinity of EUG could effectively reduce the adhesion on the surface of the film, so it could improve the fitness of gloves and other latex products to human organs and facilitate wearing and taking off. At last, adding an appropriate amount of EUL could enhance the tear performance of the composite film. When the content of EUG was 20 %, the tear strength of the film increased by 19 %, which improved the cutting resistance of the latex product. So, the NR/EUG composite film could be used to develop high-modulus, low adhesive force of surface, high tear performance and super thin latex product. • EUG is made into latex by emulsion solvent evaporation technology. • NR/EUG composite film is first prepared. • The addition of EUL can increase the modulus of NR/EUG films. • The addition of EUL can increase the tear properties of NR/EUG films. • The addition of EUL can reduce adhesion of NR/EUG films.

High-efficiency antibacterial and barrier properties of natural rubber/graphene oxide@Ag/carboxymethyl chitosan composites

ABSTRACT Natural rubber (NR) latex gloves serve as a very important barrier protection for health care workers. It is of great significance to study the barrier and antibacterial properties of NR latex products. Herein, a small amount of graphene oxide (GO) with in situ grown silver (Ag) nanoparticles was self-assembled in the NR latex by carboxymethyl chitosan (CMCS) as a cross-linking agent to form a novel NR/GO-Ag-CMCS composite with three-dimensional filler networks. The filler networks in the NR/GO-Ag-CMCS composite were formed by a strong interfacial interaction between NR macromolecules and GO-Ag-CMCS hybrids. The tensile strength and tear strength of NR/GO-Ag-CMCS composite were higher than those of pure NR film. With the increase of GO content, the filler network of NR/GO-Ag-CMCS film tended to be more complete and its barrier was stronger. Moreover, the NR/GO-Ag-CMCS composite showed excellent antibacterial performance against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The minimal inhibitory concentration values of GO-Ag-CMCS hybrid to E. coli and S. aureus were 8 and 16 μg/mL, respectively. For the NR/GO-Ag-CMCS composite with 0.1 phr GO, the diameters of its inhibition zone were 15.6 mm for E. coli and 13.6 mm for S. aureus.

Effect of Nanocrystal Cellulose Isolated from Empty Fruit Bunches (Elaeis Guineensis Jack) Addition on Morphological and Mechanical Properties of Natural Rubber Latex Product.

The research about the effect of the addition of nano crystal cellulose (NCC) isolated from empty palm bunches (EPB) on the morphological and mechanical properties of natural rubber latex products was successfully conducted. This research was carried out in three steps: i.e isolation of α-cellulose from EPB, followed by isolation NCCs from α-cellulose using H2SO4 48.84% at 45ºC for 25 minutes, and manufacture of latex compound with varying filler NCC were 0, 0.6, 1.2, 1.8, 2.4, and 3.0. Manufacturing of natural rubber product was made with pour the NRL followed by vulcanized at 120ºC for 30 minutes. The sheet of NRL product was produced later characterized its mechanical properties through tensile test and surface morphology analysis by SEM. The optimum value of the tensile test result of the NRL product sheet was at the addition of 1,2 phr of NCC with values of tensile test, elongation at break, and Young’s modulus was 3.771 MPa, 877%, and 0.430 Mpa respectively. In addition, surface morphology analysis showed that the NCC was spread evenly.

SiO2 and ZnO hybrid nanofillers modified natural rubber latex: Excellent mechanical and antibacterial properties

AbstractThe modification of polymer with nanoparticles has been proved to have good results, but the key of this method is that nanoparticles can maintain uniform dispersion in the polymer. Herein, silica (SiO2) and zinc oxide (ZnO) hybrid nanofillers were prepared by self‐made dispersion equipment to modify natural rubber latex (NRL). The results show that the uniformly dispersed nano‐SiO2 fillers increase the number of entanglements in the molecular chain of NRL, thereby improving the tensile properties. The tensile strength and elongation at break of LZ1S4.2 were increased to 32.61 MPa and 957%, respectively. The increase of the number of entanglements also makes the structure of NRL more compact, and improves the barrier performance and aging resistance. The uniformly dispersed nano‐ZnO fillers endow the NRL with excellent antibacterial properties, and the antibacterial rate (For Escherichia coli and Staphylococcus aureus) is greater than 99.9%. In addition, NRL condoms and gloves incorporating hybrid nanofillers have been proved to have good biocompatibility, and this NRL nanocomposite is expected to be applied to other NRL products.

Novel Deproteinized Natural Rubber Latex Adhesive Used in Extraoral Maxillofacial Prostheses

This study aimed to develop an adhesive for silicone maxillofacial prostheses and compared the properties with the Daro adhesive hydrobond (Factor II, Inc, Lakeside, AZ, USA). Two adhesives were developed from non-vulcanized natural rubber-based adhesives (Adhesive A) and deproteinized natural rubber latex (DNRL) products (Adhesive B) and stored at 4 °C. The Control group was the commercial Daro adhesive hydrobond (Factor II, Inc, Lakeside, AZ, USA). The physical properties (appearance, viscosity, spreadability, color, and pH) of the adhesives were measured and every week for 12 weeks after storing at 4 °C. The adhesives were characterized under scanning electron microscopy. Mechanical testing done were peel bond strength and biocompatibility testing was done using MTT assay. Physical, surface, and mechanical properties were compared with the commercial adhesive. Data analysis was done using SPSS version 24. Both adhesives were physically and chemically stable at temperature 4 °C and had suitable peel bond strength adhesives as the commercial adhesive. Hence, the adhesives can be used to adhere to the maxillofacial silicone prostheses.

ADJUSTING THE LOW MOLECULAR WEIGHT OF HYDROXYETHYL CELLULOSE AND APPLIED TO EXTRACT PROTEINS IN NATURAL RUBBER LATEX

Natural rubber latex (NRL) with “low protein content” is regarded as less allergenic latex for medical gloves, medical products, condoms, etc. Therefore, this study was conducted to strengthen the fundamental approach of making “low protein NRL” via oligosaccharide hydroxyl ethyl cellulose (oligoHEC) treatment. OligoHEC (Mw ~10,000 g/mol) is degradation product of HEC (Mw ~90,000 g/mol) by 1.5% H2O2 treatment combined with hydrothermal at temperature for 30 minutes at 121°C, pressurized rate of 0.38 mPa by autoclave equipment. OligoHECs were employed to form electrical bonds with the proteins. The target of this study is protein content of NRL ≤ 50 µg/g of rubber, we surveyed the effect of oligoHEC treatment towards the solution proteins content of NRL. Results show that oligoHEC at low concentration (0.25%) effectively extracted the proteins molecules. Interestingly, allergenic proteins content of NRL serum was decreased proportionally (< 50 µg/g of rubber) with the upsurge of oligoHEC concentration, suggesting deactivation of allergenic. These preliminary results indicate a potential approach to produce low allergenic risk NRL products with adding of oligoHEC

Measurement of 222Rn Exhalation Rate from Natural Rubber Latex Pillows Randomed from Online Market in Thailand

Radon is a natural radioactive gas, and it is increasingly interesting worldwide because it affects the human healthy and increases lung cancer risk when people receive high concentrations over extended periods of time by inhalation. The study was to measure the radon concentration, determine the radon exhalation rate, and estimate annual effective dose level in order to set up a policy on controlling the contamination of radon in the natural rubber latex products in Thailand, and the radon concentrations were measured from natural rubber latex pillows randomized from online market in Thailand by closed chamber system technique with ATMOS 12 DPX. The results showed that the equilibrium radon concentrations were ranged between 11 ± 2 and 43 ± 5 Bqm–3 with an average value of 17 ± 9 Bqm–3. All measured radon concentrations were well below the allowed maximum contamination level of radon concentration in collected samples of 148 and 300 Bqm–3, recommended by the USEPA and the ICRP, respectively. The exhalation rates from natural rubber latex pillows were ranged 12 ± 3 and 60 ± 7 mBq m–2 h–1 with an average value of 25.7 ± 14.4 mBq m–2 h–1. The annual effective doses calculated for inhalation were between 0.12 ± 0.03 and 0.43 ± 0.05 mSv y–1, and also well lower than the annual effective dose for general public (1.0 mSv y–1) recommended by the ICRP.

Measurement of cross link densities of prevulcanized natural rubber latex and latex products using low-cost near infrared spectrometer

The objective of this project is to use the four models to predict the crosslink densities based on reference method of PRM 300% using portable low-cost visible and shortwave near-infrared (Vis/SW-NIR) spectrometer across wavelengths of 350-1100 nm. The degrees of crosslink reflect on the properties of the prevulcanized (PV) latices and latex products produced and hence useful for quality control in the process of production. The four models were optimized using partial least squares regression (PLSR) that the spectra were collected from PV, PV50, thin and thick films. The use of thin and thick films was to emulate the latex products that used the PV latices. The results showed that there were almost no difference in the PV and PV50 models by the coefficient of determination (R2) and root mean square error of calibration (RMSEC) of 0.70 and 9.04 × 104 N/m2 and 0.75 and 8.59 × 104 N/m2, respectively. Among the four models, thin and thick film models had poor results indicated by the coefficient of determination (R2) and root mean square error of calibration (RMSEC) of 0.02 and 17.31 × 104 N/m2 and 0.05 and 16.63 × 104 N/m2, respectively. Based on these results, only the models of prevulcanized (PV) latices could be used for quality assessment. Hence the Vis/SW-NIR spectrometer could be a cheap alternative for crosslink density determination of PV latices and would be a beneficial tool for monitoring the process of vulcanization in the rubber industry.

Comparison of weight loss in natural rubber latex film (rubber dam) filled nanocrystal cellulose and synthetic dyes with soil burial methods

Biodegradation of natural rubber latex products filled with nanocrystal cellulose from peanut shell is carried out by soil burial methods with and without using fertilizer. Testing is done by calculating the loss of sample weight for 5 weeks with observation every 1 week. Samples were tested the morphology using Scanning Electron Microscope (SEM) and Fourier Transform Infra Red (FTIR). Natural rubber latex film samples showed that the loading of nanocrystal cellulose fillers from peanut shells was biodegradable faster in soil burial method with addition of fertilizer in soil compared to no addition of fertilizer.

Mangosteen peel and seed as antimicrobial and drug delivery in rubber products

AbstractGarcinia mangostana Linn. or mangosteen is a tropical superfruit with an excellent taste. The peel and seed of mangosteen waste can be used in medical, cosmetic, and health‐care applications. Both mangosteen peel and seed have outstanding antibiotic properties and are suitable for use as bio‐fillers in natural rubber latex products such as medical gloves, rubber transdermal patches, rubber toys, and rubber‐health care products. In addition, mangosteen seed composed of griseofulvin polyethylene glycol [(C2H4O2)n]1‐x (C17H17ClO6)x is useful for treating osteoarthritis of the knee, similar to commercial glucosamine (amino sugar). Adding mangosteen peel and mangosteen seed in rubber gloves and rubber patches, respectively, is an alternative form of antimicrobial and drug delivery replacing taking a tablet. This study compared the characteristics and properties of mangosteen peel with silver nitrate (AgNO3) and compared the characteristics and properties of mangosteen seed with commercial glucosamine using the film casting dipping process. The obtained natural rubber latex gloves with added mangosteen peel powder had a good appearance with a high contact angle (resulting in hydrophobicity and low wettability with water equal to 130.67° ± 2.08°), good mechanical properties (high percentage of elongation at break 815.72 ± 54.67%, high tensile strength 64.59 ± 13.54 MPa, good stiffness 296.50 ± 48.32 N/m, and high Young's modulus 29.65 ± 4.83 MPa), and as it was non‐toxic to skin it was suitable for application in medical gloves and transdermal patches. The natural rubber patches added with mangosteen seed had high wettability and good mechanical properties. The Fourier‐transform infrared (FTIR) spectra of mangosteen seed were consistent with the FTIR spectra of commercial glucosamine.

Pengaruh Konsentrasi Asam Sulfat (H2SO4) pada Hidrolisa Tongkol Jagung (Zea mays) Menjadi Nanokristal Selulosa sebagai Filler Penguat pada Produk Lateks Karet Alam

This research studied about the effect of concentrations sulfuric acid (H2SO4) on the hydrolysis process of corn cobs waste to manufacture of cellulose nanocrystal (NCC) which will be applied as fillers in natural rubber latex. This study began with a pre-vulcanization process of natural rubber latex at a temperature of 70 oC and followed by a vulcanization process at 110 oC for 10 minutes. The results of the testing of physical properties indicate that the higher amount of NCC loading will result in higher crosslinked denotes, while the results of testing the mechanical properties indicate that the maximum value is achieved at the loading of NCCs as much as 6 phr. The mechanical test results supported by the analysis of Scanning Electron Microscopy (SEM) showing the NCC have spread well. Characterization of the Transform Electron Microscope (TEM) shown the resulting of NCC was spherical shape with the size of NCC produced for each concentration of sulfuric acid (H2SO4) 45%, 55%, and 65% respectively 57.65 nm; 28.43 nm; and 82.61 nm with an amount of each 0.849 g; 1,824 g; and 0.681 g. The mechanical and physical properties of the optimum natural rubber latex products occurred in the loading of nanocrystal cellulose with a number of 6 bsk, where the values ​​of cross-connect density, tensile strength, elongation at break, M200 and M300 were respectively 10.6234 2Mc-1x10- 5; 18.2 MPa; 780%; 2.23 MPa and 2.7 MPa.

Anti-blooming effect of graphene oxide on natural rubber latex composite films

Owing to its water-dispersibility and compatibility with natural rubber latex (NRL) in an aqueous medium, graphene oxide (GO), the precursor of graphene, has been often employed as an emerging filler for improving the mechanical and barrier properties of NRL products. Herein, to solve the blooming problem of NRL products, we studied the anti-blooming effect of GO in NRL-GO composites. The NRL-GO composite films were prepared by latex compounding followed by solution casting. Scanning electron microscopy and energy dispersive X-ray spectrometry were employed to characterize the NRL/GO microstructure and analyze the anti-blooming effect. The results reveal significant enhancement of the anti-blooming performance of the composite films with GO, even at a GO content as low as 0.5 wt%. The origin of the anti-blooming effect of GO is discussed in terms of three factors: 1) inner-layered structure of GO in the composite films, 2) interaction between GO and the additives, and 3) surface property of the composite films. This work not only provides a new strategy to overcome the severe blooming issue of NRL products, but also expands the practical application of GO in traditional NRL industry.

The Effect of Drying Temperature on Natural Rubber Latex (NRL) Films with Modification of Nanocrystal Cellulose (NCC) Filler

The process of vulcanization in the formation of NRL products is influenced by temperature at which the drying temperature has important role in the process of crosslinking that can affect the mechanical properties of NRL films produced. This study discusses about the effect of drying temperature on the mechanical properties of NRL films with modification of corn cob NCC filler obtained from the hydrolysis process with sulfuric acid. NCC filler is made of dispersion system involving polyvinylpyrrolidone (PVP) as a dispersion agent. The resulting product was prepared by mixing NRL compound with modified NCC filler with a polyvinylpyrrolidone dispersion agent by coagulant dipping method. The coagulant utilized in the process of formation of NRL films used 10% calcium nitrate and NRL films which formed with variation of drying temperature 100°C, 110°C, and 120°C for 20 minutes. In this study mechanical properties such as tensile strength, elongation at break, and M100 dan M300 of NRL films has been analyzed. The results showed that mechanical properties such as elongation at break increased with the higher of drying temperature, it was different with tensile strength, M100 and M300. In addition, in this study crosslink density and morphological of NRL films were also analyzed.

Quantification of protein and latex allergen content of various natural rubber latex products.

Introduction: The use of natural rubber latex (NRL) products can cause IgE-mediated allergic reactions in exposed people. The aim of this study was to quantify the content of protein and latex allergens of currently available NRL products to estimate the allergenic potential of these products. Methods: 14 household articles (pacifiers, baby bottle nipples, condoms, household and disposable gloves, toy balloons, and Band-Aids) as well as 18 NRL examination gloves currently used by healthcare workers were investigated. Extracts of the examination gloves were prepared according to the standard method DIN EN 455-3, which contains requirements and testing for biological evaluation of single use medical gloves. The protein content was determined with a modified Lowry method. Latex allergen content was measured using an IgE-inhibition immunoassay with a mix of serum-sensitized patients as detection antibody sources and the latex ImmunoCAP as solid phase. The allergens Hev b 1, 3, 5, and 6.02 were determined using available immunoassays. Results: In 5 out of 18 examination gloves, the protein content was under the detection limit. The other 13 gloves contained protein between 7.1 and 92.3 µg protein/g material. Five glove brands contained protein concentrations above the recommended reference value of 30 µg protein/g material. Latex allergen could be measured in 12 out of 18 NRL gloves. In only 3 gloves could none of the allergens Hev b 1, 3, 5, and 6.02 be detected. Protein and Hev b 1 could be measured in the examined childcare products, while the concentrations of the latex allergens Hev b 3, 5, and 6.02 were mostly under the detection limit. Boiling of childcare products led to a reduction of protein and allergen content. In some of the other daily-used NRL articles, the protein and allergen contents were even higher than in gloves. Conclusion: Our study demonstrated that protein, and particularly latex allergens, were detectable in currently available examination gloves as well as in household articles whereby a risk for sensitization and/or induction of allergic symptoms could not be excluded.

Development of an Economical Method to Reduce the Extractable Latex Protein Levels in Finished Dipped Rubber Products.

Natural rubber latex (NRL) allergy is caused by the extractable latex proteins in dipped rubber products. It is a major concern for the consumers who are sensitive to the allergenic extractable proteins (EP) in products such as NRL gloves. Objective of this research was to develop an economical method to reduce the EP in finished dipped NRL products. In order to reduce the EP levels, two natural proteases, bromelain from pineapple and papain from papaya, were extracted and partially purified using (NH4)2SO4. According to the newly developed method, different glove samples were treated with a 5% solution of each partially purified enzyme, for 2 hours at 60°C. Residual amounts of in treated samples were quantified using the modified Lowry assay (ASTM D5712-10). Bromelain displayed a 54 (±11)% reduction of the EP from the dipped rubber products, whereas it was 58 (±8)% with papain. These results clearly indicate that the selected natural proteases, bromelain, and papain contribute significantly towards the reduction of the total EP in finished NRL products. Application of bromelain enzyme for the aforementioned purpose has not been reported up to date, whereas papain has been used to treat raw NRL towards reducing the EP.

Quantitative Analysis of AntiHevea brasiliensis Antibody Cross-Reactivity against Taraxacum kok-saghyz Latex Proteins Demonstrates Significantly Reduced Antibody Recognition

The annual plant Taraxacum kok-saghyz, commonly called Russian dandelion, has recently gained commercial attention as an alternative source to the rubber tree, Hevea brasiliensis, for natural rubber latex. While producing rubber of equivalent quality, the potential application of TKS latex for hypoallergenic products remains to be determined. In order to quantify the allergenicity of TKS latex proteins, we compared the extent of anti-Hevea latex polyclonal and monoclonal antibody cross-reactivity toward Hevea latex proteins to that of TKS latex proteins by quantitative ELISA methods and semi-quantitative image densitometry. ELISA measurement of polyclonal antibody recognition toward TKS latex proteins was on the order of one-tenth relative to equal amounts of Hevea latex protein, while recognition by the monoclonal antibody was below 2%. Immunoblots confirmed significantly reduced polyclonal antibody recognition toward TKS latex proteins, in the same range as the cross-reactivity exhibited toward the rubber-producing plant, Lactuca sativa and Glycine max, a non-rubber-producing plant. Despite the presence of cross-reactivity, these quantitative results support TKS as an alternative source of latex that may require lessintensive processing for the reduction of antigenic proteins in the manufacture of hypoallergenic natural rubber latex products.

Effect of Different Preparation Methods on Crosslink density and Mechanical Properties of Carrageenan filled Natural Rubber (NR) Latex Films

This research discussed the influenced of different preparation methods of Carrageenan fillers as new natural biodegradable additives in Natural Rubber (NR) latex compound. NR latex compounds with addition of 2 phr Carrageenan fillers was prepared through normal pre-vulcanization method which the NR latex compound was subjected to 70oC denoted as Method 1. The preparation of NR latex compounds with 2 phr Carrageenan fillers without temperature is denoted as Method 2. The unfilled NR Latex films also was prepared as a control through Method 1. The crosslink density and mechanical properties of NR Latex films were investigated via swelling test and mechanical testing (tensile and tear) respectively. The swelling test results shows that Method 2 have highest crosslink density where the crosslink density and mechanical properties via Method 1 shows a decreased value. This may contribute from the hydration of carrageenan at temperature of 40oC-70oC. The experimental results indicate that the addition of carrageenan with elimination of pre-vulcanization step is mainly responsible for the enhancement of crosslink density and mechanical properties compared to Method 1. Method 2 gives higher crosslink density, tear strength and lower modulus as evaluated from the mechanical properties. Carrageenan can be added as natural filler in NR Latex films with gives better interaction between rubber matrix and fillers with softer NR latex films which required in NR latex products especially gloves.

Effect of Aging on Mechanical Properties of Natural Rubber Latex Products Filled with Alkanolamide-Modified Cassava Peel Waste Powder (CPWP)

The effect of aging on mechanical properties of natural rubber latex (NRL) products filled with alkanolamide-modified cassava peel waste powder (CPWP) was studied. CPWP used as fillers was prepared by milling and sieving it until the size of 100 mesh. The powder then was dispersed in a suspension containing water and alkanolamide in order to modify the prepared powders. The dispersion system of 10 pphr (part per hundred rubber) then was added into NRL matrix followed by pre-vulcanization at 70°C for 10 minutes. The NRL compound then were casted into films by coagulant dipping method then dried at 120°C for 10 minutes. Afterwards, the films were allowed to cool at room temperature for 24 hours before being aged in a circulation of hot air for 24 hours at 70°C. The properties such as tensile strength, tensile modulus, and elongation at break were evaluated between the aged samples and the unaged samples. From this study, it showed that the aged films have increasing value of tensile strength and tensile modulus while the value of elongation at break decreases. These datas are supported by Scanning Electron Microscope (SEM) micrographs which indicate that the change of morphology in NRL films occurs before and after aging.