Printer Friendly
The Free Library
22,728,960 articles and books

A new grade of natural rubber latex: NC360.



One of the greatest challenges for the natural rubber latex latex, emulsion of a polymer (e.g., rubber) in water (see colloid). Natural latexes are produced by a number of plants, are usually white in color, and often contain, in addition to rubber, various gums, oils, and waxes.  industry has been the latex protein allergy allergy, hypersensitive reaction of the body tissues of certain individuals to certain substances that, in similar amounts and circumstances, are innocuous to other persons. Allergens, or allergy-causing substances, can be airborne substances (e.g.  problem. Natural rubber latex is produced from a milky milky (mil´ke)
1. having the appearance of milk; whitish, cloudy, fluid.

2. filled with or consisting of milk or a milklike fluid.
 white liquid extracted from the hevea brasiliensis Noun 1. Hevea brasiliensis - deciduous tree of the Amazon and Orinoco Rivers having leathery leaves and fragrant yellow-white flowers; it yields a milky juice that is the chief source of commercial rubber
caoutchouc tree, Para rubber tree
 tree. The tree incorporates antioxidants Antioxidants
Substances that reduce the damage of the highly reactive free radicals that are the byproducts of the cells.

Mentioned in: Aging, Nutritional Supplements

antioxidants,
n.
, carbohydrates Carbohydrates
Compounds, such as cellulose, sugar, and starch, that contain only carbon, hydrogen, and oxygen, and are a major part of the diets of people and other animals.

Mentioned in: Laxatives

carbohydrates,
n.
, lipids lipids, a broad class of organic products found in living systems. Most are insoluble in water but soluble in nonpolar solvents. The definition excludes the mineral oils and other petroleum products obtained from fossil material.  and proteins with the desirable polymer polyisoprene. It is these proteins which have been implicated im·pli·cate  
tr.v. im·pli·cat·ed, im·pli·cat·ing, im·pli·cates
1. To involve or connect intimately or incriminatingly: evidence that implicates others in the plot.

2.
 in the cause of these allergies Allergies Definition

Allergies are abnormal reactions of the immune system that occur in response to otherwise harmless substances.
Description

Allergies are among the most common of medical disorders.
. In this article we will discuss a new grade of natural rubber latex developed in response to the latex protein allergy issue. The product is called NC360 latex. We will discuss the properties of NC360 and compare them to standard grades of natural rubber latex. Then we will discuss producing gloves using NC360. We will cover the processing challenges we have encountered producing a glove glove, hand covering with a separate sheath for each finger. The earliest gloves, relics of the cave dwellers, closely resembled bags. Reaching to the elbow, they were most probably worn solely for protection and warmth.  that will meet ASTM ASTM
abbr.
American Society for Testing and Materials
 standards. We will review the physical properties of the gloves produced from NC360. We will demonstrate that NC360 is a commercially, viable product, and with NC360 we enable the natural rubber latex industry to produce safer products.

Properties

All grades of NR latex start with a material called field latex that is tapped from the hevea brasiliensis tree. This material is only 33% natural rubber along with several other naturally occurring chemicals. A typical composition of field latex is listed in table 1.
Table 1 - composition of field latex

                              %

Total solids content         36
Dry rubber content           33
Proteinous substances   1 - 1.5
Resinous substances     1 - 2.5
Ash                     Up to 1
Sugars                        1
Water                   Ad. 100


There is a significant amount of non-rubber solids (NRS NRS Nevada Revised Statutes
NRS National Runaway Switchboard (Chicago, IL)
NRS Natural Reserve System (University of California)
NRS National Readership Survey
NRS National Relay Service
) present in field latex, about 3.0 - 6.0%. The proteins that can cause latex allergies latex allergy Allergy medicine An IgE-mediated sensitivity to latex proteins Clinical Anaphylaxis, angioedema, asthma, conjunctivitis, contact urticaria, rhinitis, following sensitization to latex allergens; LA is common, affects ±7% of US population, ≥  are part of the NRS portion. The field latex is processed into commercial grades of NR latex. This usually involves concentrating the field latex to higher total solids. The main methods of concentration are centrifuging and creaming. Ammonia ammonia, chemical compound, NH3, colorless gas that is about one half as dense as air at ordinary temperatures and pressures. It has a characteristic pungent, penetrating odor.  and other preservatives preservatives,
n.pl food additives that hinder spoilage by reducing the growth of microorganisms. Include nitrates and nitrites, benzoates and sulfites, and many others.
 are added for preservation. ASTM/ISO standards have established standards for three different types of latex based on concentration method and preservative preservative

Any of numerous chemical additives used to prevent or slow food spoilage caused by chemical changes (e.g., oxidation, mold growth) and maintain a fresh appearance and consistency. Antimycotics (e.g.
 systems. The specifications are listed in table 2.
Table 2 - requirements for specified latex types

                                    Type 1 (*)      Type 2      Type 3
                                                      (**)       (***)

Total solids, min., %                     61.5        66.0        61.5
Dry rubber content (DRC), min., %         60.0        64.0        60.0
Total solids minus dry rubber              2.0         2.0         2.0
  content, max., %
Total alkalinity calculated as      0.60 min.    0.55 min.   0.29 max.
  ammonia, as % latex
Sludge content, max., %                   0.10        0.10        0.10
Coagulum content, max., %                0.050       0.050       0.050
KOH number, max.                          0.80        0.80        0.80
Mechanical stability, s, min.              650         650         650
Copper content, max., % of              0.0008      0.0008      0.0008
  total solids
Manganese content, max., % of           0.0008      0.0008      0.0008
  total solids
Color on visual inspection               No pronounced blue or gray
Odor after neutralization with              No putrefactive odor
  boric acid

(*) Centrifuged natural latex preserved with ammonia only or by
formaldehyde followed by ammonia.

(**) Creamed natural latex preserved with ammonia only or by
formaldehyde followed by ammonia.

(***) Centrifuged natural rubber latex preserved with low
ammonia with other necessar perservatives.


A review of the ASTM specifications from table 2 and the typical properties in table 3 highlights the differences between the NC360 and the three types of commercially available NR latex. These differences are significant as they affect the production of gloves from the NC360.
Table 3 - typical properties of commercially available natural
rubber latex and NC360

                                 Type 1   Type 2   Type 3     NC360

Total solids, %                    61.7     67.5     61.7      65.8
Dry rubber content (DRC), %        60.2     66.3     60.2      65.5
Total solids minus dry rubber
  content, %                        1.5      1.2      1.5       0.3
Total alkalinity calculated as
  ammonia, as % latex              0.70     0.60     0.24      0.60
Sludge content, %                  0.05     0.10     0.05     <0.01
Coagulum content, %               0.010    0.005    0.010     0.001
KOH number                         0.62     0.65     0.67      0.40
Mechanical stability, s           1,200    1,500    1,000     1,500
Copper content, % of total
  solids                         0.0003   0.0003   0.0003   <0.0001
Manganese content, % of total
  solids                         0.0001   0.0001   0.0001   <0.0001
Color on visual inspection             No pronounced blue or gray
Odor after neutralization with
  boric acid                              No putrefactive odor

Extractable protein content -
  cast films

ASTM D5712-95 ([micro]g
  protein/g of latex film         1,900      860    2,000       <28
LEAP - ELISA, ([micro]g of
  protein/g of latex film         1,100      870    1,200       1.2


The non-rubber solids (NRS) are the difference between total solids content (TSC TSC Thestreet.com (stock symbol)
TSC Time Stamp Counter
TSC Tuberous Sclerosis Complex
TSC Tractor Supply Company
TSC Terrorist Screening Center (Department of Homeland Security) 
) and dry rubber content (DRC DRC Democratic Republic of Congo
DRC Down (Stage) Right Center
DRC Director(ate) of Reserve Components
DRC Disability Rights Commission (United Kingdom) 
). NC360 has a very low level of NRS. This is a very important difference. By removing the non-rubber solids from the latex we also removed the protein. Unfortunately, there are many naturally occurring chemicals in latex that have beneficial properties to the latex and material made from the latex. The proteins help facilitate vulcanization vulcanization (vŭl'kənəzā`shən), treatment of rubber to give it certain qualities, e.g., strength, elasticity, and resistance to solvents, and to render it impervious to moderate heat and cold. , the lipids react with ammonia to produce soap which gives the latex mechanical stability, the resins resins,
n.pl complex, insoluble, sticky substances secreted by plants. Used as astringents, antimicrobials, and antiinflammatories, and are burned as incense. Can cause oral ulcers and epidermal irritations.
 are a very effective natural antioxidant antioxidant, substance that prevents or slows the breakdown of another substance by oxygen. Synthetic and natural antioxidants are used to slow the deterioration of gasoline and rubber, and such antioxidants as vitamin C (ascorbic acid), butylated hydroxytoluene  which gives products good aging properties. This significantly lower NRS results in the TSC not meeting the ASTM specification for type 2 latex even though the DRC meets the limit. This is not an issue in glove production since most formulations lower the TSC of the compound to 50%.

Mechanical stability is a measure of how much shear force shear force

Force acting on a substance in a direction perpendicular to the extension of the substance, as for example the pressure of air along the front of an airplane wing. Shear forces often result in shear strain.
 the latex can handle before the latex destabilizes and forms coagulum coagulum /co·ag·u·lum/ (ko-ag´u-lum) pl. coa´gula   [L.] clot (1).

co·ag·u·lum
n. pl. co·ag·u·la
1. A clot; a curd.

2.
. To become a commercially viable product, NC360 must have enough mechanical stability to survive the rigors of pumping, transporting, mixing and compounding. Several components of the non-rubber solids play a role in developing mechanical stable latex. The lipids react with ammonia to form soaps in natural rubber latex. The proteins also play a role in stability. Since we have removed these materials, we had to find the proper mix of surfactants that would give us the requisite amount of mechanical stability.

The KOH KOH
The chemical formula for potassium hydroxide, which is used to perform the KOH test. The tests is also called a potassium hydroxide preparation.

Mentioned in: KOH Test


KOH

potassium hydroxide.
 and VFA VFA

volatile fatty acids.
 numbers are used to indicate the state of preservation of natural rubber latex. Natural rubber latex is susceptible to bacterial contamination. As bacteria grow and reproduce re·pro·duce
v.
1. To produce a counterpart, an image, or a copy of something.

2. To bring something to mind again.

3. To generate offspring by sexual or asexual means.
 in the latex they produce volatile fatty acids Volatile fatty acids are fatty acids with a carbon chain of six carbons or fewer.

They can be created through fermentation in the intestine.

Examples include:
  • acetate
  • propionate
  • butyrate
External links
 such as formic for·mic  
adj.
1. Of or relating to ants.

2. Of, derived from, or containing formic acid.



[From Latin form
, acetic acetic /ace·tic/ (ah-se´tik) (ah-set´ik) pertaining to vinegar or its acid; sour.

acetic

pertaining to vinegar or its acid; sour.
 and propinoic. These fatty acids fatty acid, any of the organic carboxylic acids present in fats and oils as esters of glycerol. Molecular weights of fatty acids vary over a wide range. The carbon skeleton of any fatty acid is unbranched. Some fatty acids are saturated, i.e.  are metabolic by-products of the bacteria so by measuring its content in the latex you have a measure of bacterial activity. The KOH number measures the total acid content in the latex. The VFA measures only the amount of volatile fatty acids in the latex. Bacterial activity can adversely affect NR latex properties rendering the latex useless in industrial processes. The NC360 must remain stable from the time of production until its delivery and use at the customer. In table 4, we show that NC360 remains very stable up to one year after production. This is another benefit of removing the NRS. The nutrients the bacteria need to survive have been removed from the NC360.
Table 4 - changes in KOH and VFA number

Latex type                  Type 1   Type 2   NC360

Initial KOH number            0.45     0.55    0.33
KOH number after 3 months     0.66     0.68    0.33
Initial VFA number           0.008    0.007   0.006
VFA number after 3 months    0.008    0.007   0.005


Two other tests of interest are the ZOV and the protein content. The ZOV, or zinc oxide zinc oxide, chemical compound, ZnO, that is nearly insoluble in water but soluble in acids or alkalies. It occurs as white hexagonal crystals or a white powder commonly known as zinc white.  viscosity test, is a measure of chemical stability of NR latex. It can indicate sensitivity toward zinc oxide. It is measured as a viscosity increase after zinc oxide is added to the latex. Zinc oxide is a very common ingredient in natural rubber latex compounding. It is a cure activator activator /ac·ti·va·tor/ (ak´ti-va?ter)
1. a substance that combines with an enzyme to increase its catalytic activity.

2. a substance that stimulates the development of a specific structure in the embryo.
 for NR latex. It enables you to efficiently cure natural rubber latex products. Latex that is sensitive to zinc oxide can go through dramatic increases in viscosity up to 10 times the original viscosity. This can make it very difficult to produce any product with NR latex. NC360 is very insensitive in·sen·si·tive  
adj.
1. Not physically sensitive; numb.

2.
a. Lacking in sensitivity to the feelings or circumstances of others; unfeeling.

b.
 to zinc oxide. Using the ZOV test we have found the viscosity unchanged or actually dropped up to an hour. NC360 will remain stable through the compounding process.
Table 5 - ZOV results, cps (ref. 1)

Time, min.   Type 1   Type 2   NC360

     2        100      140      120
     5        110      190      120
    10        120      200      120
    20        130      210      130
    30        132      220      132
    40        144      230      140
    50        144      244      150
    60        155      260      154
Table 6 - compound formulations

Trial                            1          2          3

Total solids, %              30.00      33.00      32.74
Soap (non-ionic), phr                                0.2
Sulfur, phr                  0.800      0.645      0.800
ZnO, phr                       0.7        0.8        0.8
Accelerator
(dithiocarbamate), phr        1.00       1.12       1.12
Precure, chloroform no.         2+         2+         2+
Cure time, min.            15 - 20    15 - 20    15 - 20
Cure temp., [degrees] C   80 - 110   80 - 110   80 - 110
Leach time, min.                 2          2          2
Leach temp., C             45 - 55    55 - 60    55 - 60
Aqueous coagulant
Calcium nitrate, %             8.0       12.0       12.0
Calcium carbonate, %           3.0        2.5        2.5


Since the advent of the allergy issue, it has become very important to measure the protein content of latex and latex products. ASTM has established D5712-95 for measuring protein in NR. The LEAP-ELISA test method is another test method used to measure protein content. Table 3 shows typical protein results for the three ASTM types and NC360. The results are the amount of extractable protein from air dried cast films.

Experiment

The novel properties of NC360 presented several processing difficulties. To test NC360 in a commercial environment, we ran three different trial runs on standard equipment.

Results and discussion

The results, from the first trial are shown in table 7. The first trial run used a standard glove formulation on a commercial glove line. Observations made during the trial run were:

* Small coagulum was found in the dipping tank. Adjustments to the surfactants will be necessary.

* At the same curing time In the annealing procedure could be divided into 3 stages:heating to a particular temperature, keeping for a period of time and cooling to room temperature. The curing time is the hold time of the 2nd stage.  and temperature, the gloves are under-cured, thus the gloves had low modulus See modulo. . Due to the absence of the non-rubber solids, the cure package will need adjustments to compensate.

* The compound was insensitive to calcium nitrate calcium nitrate
n.
Colorless crystals, Ca(NO3)2·4H2O, used in explosives.

Noun 1. calcium nitrate
. Increase the calcium nitrate solution concentration to get better film pick up.
Table 7

Physical properties     Unaged        Aged 22 hrs.
                                 @ 100 [degrees] C

Tensile strength, MPa     18.5                17.8
Elongation, %              850                 820
Modulus @ 300%, MPa        2.7                 2.9


With adjustments to the formulation, we were able to overcome the technical problems encountered in trial 1. In trials 2 and 3, we needed to see if the gloves produced could meet ASTM standards on physical properties. In trial 2, the physical properties are near the minimum. Upon aging they failed to retain their physical properties to meet the ASTM requirements. The protein content had an increasing trend during the trial. This is only seen in the D5712-95 test results. The LEAP-ELISA test results do not show this same behavior. This could indicate that the D5712-95 is picking up false positives from the compounding ingredients. It also shows that the compounding ingredient concentrations are increasing in the leach leach  
v. leached, leach·ing, leach·es

v.tr.
1. To remove soluble or other constituents from by the action of a percolating liquid.

2.
 tank during the trial run. Gloves from the end of the run were not leached as effectively. For trial 3, the formulation was changed to correct for these problems. The refresh rate The number of times per second that a device, such as a display screen or DRAM chip, is re-energized. See vertical scan frequency and dynamic RAM.

(hardware) refresh rate
 for the water in the leach tank was also increased. The gloves' physical properties on unaged and aged meet the ASTM specifications. The D5712-95 results do not show protein content increasing with time, but the average content is significantly higher. This is probably due to the increased accelerator content. The LEAP-ELISA test results have a lower average in trial 3 (table 9) than trial 2 (table 8).
Table 8

    Glove         Time into       Protein content
    type             run

                                 ASTM         LEAP
                               D5712-95      ELISA
                              [micro]g/g   [micro]g/g

1   Powder          1 hr.        <28           4.5
2   Powder          3 hrs.       <28           4.4
3   Powder         15 hrs.       <28           4.4
4   Powder         21 hrs.       <28           5.3
5   Powder free     1 hrs.       <28          23.8
6   Powder free    15 hrs.        42          17.6
7   Powder free    18 hrs.       <28           3.3
8   Powder free    21 hrs.       <28          23.0
9   Powder free    24 hrs.       <28          27.5
Table 9

                                                          Aged 22
                                                          hrs. @
                                  Unaged                    100
                                                        [degrees] C

                      Modulus   Tensile    Elongation     Modulus
                      @ 300%    strength    at break       @300%
  Date       Time      (MPa)     (MPa)        (%)          (MPa)

 1 6/3/99   4:30 PM    1.16      25.21        895          0.86
 2 6/3/99   1:00 AM    1.19      19.84        862          0.87
 3 6/4/99   9:00 AM    1.20      24.58        860          0.83
 4 6/4/99   4:00 PM    1.27      31.49        840          0.88
 5 6/4/99   2:20 AM    1.27      25.36        846          0.92
 6 6/5/99   9:00 AM    1.40      25.41        824          0.86
 7 6/5/99   4:30 PM    1.20      24.42        801          0.87
 8 6/5/99   3:25 AM    1.29      25.26        852          0.96
 9 6/6/99   9:20 AM    1.24      24.17        840          0.89
10 6/6/99   1:00 AM    1.29      24.27        829          0.86

                        Aged 22 hrs. @ 100
                           [degrees] C            Protein content

                      Tensile    Elongation      ASTM         LEAP
                      strength    at break     D5712-95      ELISA
  Date       Time      (MPa)        (%)       [micro]g/g   [micro]g/g

 1 6/3/99   4:30 PM    20.32        945          102          0.4
 2 6/3/99   1:00 AM    19.25        894           51          0.5
 3 6/4/99   9:00 AM    16.12        849           84          0.5
 4 6/4/99   4:00 PM    17.72        820           33          0.7
 5 6/4/99   2:20 AM    19.79        879           69          0.5
 6 6/5/99   9:00 AM    19.16        730           72          0.5
 7 6/5/99   4:30 PM    16.96        873           84          0.5
 8 6/5/99   3:25 AM    19.13        892          105          0.5
 9 6/6/99   9:20 AM    17.75        908           96          0.5
10 6/6/99   1:00 AM    18.26        873           78          0.6
Table 10

                                                          Aged 22
                                                          hrs. @
                                  Unaged                    100
                                                        [degrees] C

                      Modulus   Tensile    Elongation     Modulus
                      @ 300%    strength    at break      @ 300%
  Date       Time      (MPa)     (MPa)        (%)          (MPa)

 1 6/3/99   4:30 PM    1.16      25.21        895          20.32
 2 6/3/99   1:00 AM    1.19      19.84        862          19.25
 3 6/4/99   9:00 AM    1.20      24.58        860          16.12
 4 6/4/99   4:00 PM    1.27      31.49        840          17.72
 5 6/4/99   2:20 AM    1.27      25.36        846          19.79
 6 6/5/99   9:00 AM    1.40      25.41        824          19.16
 7 6/5/99   4:30 PM    1.20      24.42        801          16.96
 8 6/5/99   3:25 AM    1.29      25.26        852          19.13
 9 6/6/99   9:20 AM    1.24      24.17        840          17.75
10 6/6/99   1:00 AM    1.29      24.27        829          18.26

                        Aged 22 hrs. @ 100
                            [degrees] C           Protein content

                      Tensile    Elongation      ASTM         LEAP
                      strength    at break     D5712-95      ELISA
  Date       Time      (MPa)        (%)       [micro]g/g   [micro]g/g

 1 6/3/99   4:30 PM     945         0.86         102          0.4
 2 6/3/99   1:00 AM     894         0.87          51          0.5
 3 6/4/99   9:00 AM     849         0.83          84          0.5
 4 6/4/99   4:00 PM     820         0.88          33          0.7
 5 6/4/99   2:20 AM     879         0.92          69          0.5
 6 6/5/99   9:00 AM     730         0.86          72          0.5
 7 6/5/99   4:30 PM     873         0.87          84          0.5
 8 6/5/99   3:25 AM     892         0.96         105          0.5
 9 6/6/99   9:20 AM     908         0.89          96          0.5
10 6/6/99   1:00 AM     873         0.86          78          0.6


References

(1.) Latex Foam Rubber foam rubber
n.
A light firm spongy rubber made by beating air into latex and then curing it. Foam rubber has a wide range of uses including upholstery and insulation.

Noun 1.
, E.W. Madge, John Wiley John Wiley may refer to:
  • John Wiley & Sons, publishing company
  • John C. Wiley, American ambassador
  • John D. Wiley, Chancellor of the University of Wisconsin-Madison
  • John M. Wiley (1846–1912), U.S.
 & Sons, NY, 1962) Data from Hoe Hai San table 5 pp. 64-65.
COPYRIGHT 2000 Lippincott & Peto, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2000, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

 Reader Opinion

Title:

Comment:



 

Article Details
Printer friendly Cite/link Email Feedback
Comment:A new grade of natural rubber latex: NC360.
Author:Flannery, Mathew
Publication:Rubber World
Article Type:Statistical Data Included
Geographic Code:1USA
Date:Nov 1, 2000
Words:2702
Previous Article:Vulcanator granulator reduces rubber bales and processing time.
Next Article:Advances and developments in NR.
Topics:



Related Articles
Quality management in the latex laboratory.
Latex allergies from right out of thin air?
The facts about latex allergies: understanding who might be affected.
High quality natural latex.
Latex conference held in Akron, OH.
Dip Molding.
EDITORIAL.
Advances and developments in NR.
Natural rubber coating: A new trend for the rubber tree plantation in Brazil.

Terms of use | Copyright © 2014 Farlex, Inc. | Feedback | For webmasters