Low Protein Latex for Dipped Goods

Beng Thye, Lim., Swee Hua, Tan.

Abstracts

Studies by previous researchers showed that NR latex contains about 0.95% of rubber protein.  They are of various molecular weights but the majority are in the range of 10-50KD, of which those of 14-30KD do cause allergenic reaction to some users.

This paper presents results from comparative study of EP (Extractable Protein) and AP (Antigenic Protein) of some commercial latex articles produced from normal latex concentrate and those produced from low protein latex. 

The results showed that over the years, much improvement has been made by Malaysian Gloves Manufacturers in reducing EP in gloves.  From commercial examination glove samples studied, results obtained show that 38% with EP <50ppm, 12% with EP between 51-100ppm and 50% with EP >200ppm but less than 400ppm. AP results of these gloves were split equally with 50% below 10ppm and 50% above 10ppm.  Whereas gloves made from low protein latex gave EP of unleached gloves consistently below 100ppm and those leached consistently below 50ppm by both ASTM and RRIM modified Lowry method; AP by ASTM method are all below 5ppm.

One can conclude from these results that to ensure consistently low EP and AP in latex articles, the use of low protein latex as starting material is essential.

 1.         INTRODUCTION

Natural  Rubber  (NR)  latex  contains  about  0.95%  of  rubber  protein. These  proteins  are  known  to  be present   are  as  follows;

i).    Rubber  fraction     -           27.2%

ii).   Serum  fraction       -           47.5%

iii).  Bottom  fraction      -           25.3%

Rubber  protein  are  of  various  molecular  weight  but   the  majority  in  the  range  of  10 – 50kD.  Studies   show  protein  of  14 – 30kD  does  cause  allergenic  reaction  to  some  users.

Studies  by  Dr.  K. Turjanmaa  and  MRB  has  shown  60%  of  the  hypersensitive    persons  have  no allergic  response  to  gloves with  extractable  protein below   400ppm  and  100%  of  negative  responses  were  observed  at  EP  below  100ppm .

2.         REMOVAL  OF  RUBBER  PROTEIN

In  the  market  today  we  can  find  various  brands  of  gloves  with  low  EP.  Most  of  these  gloves  are  either  chlorinated  or  have  undergone  post  washing / treatment  to  remove  the  EP.   As  such,  the  removal  of  these  proteins  in  rubber  articles  will  reduce  significantly  the  risk  of  Type  I  Allergy.

Protein  in  NR  can  be  removed  either  from  wet  latex   stage  or  from  dry  rubber  articles.   Rubber  protein in latex  can  be  removed  by  the  following  methods;

i).    Biological  process  - enzymatic  digestion

ii).   Chemical  process  - denaturing  of  protein

iii).  Physical  process    - removal  of  protein  i.e.  centrifugation

Whereas  protein  in  rubber  articles  can  be  removed  by;

i).     Multiple  washing - leaching  with  water  or  enzyme  in  water

ii).    Chlorination

iii).   Polymer  coating -  Barrier

As  we  know  clonal  difference  do  not  have  significant  variance  in  term  of  total  available  proteins.  But   our  own  studies  have  led  us  to  postulate  that  clonal  differences  and  seasonal  changes  do  have  effects  on   total  water  extractable  proteins.  This  was  evidenced  from  the  wide  range  of   EP  of  unleached  film  made  from  different  batches  of  latex  concentrate  at  different  times  of  the  year.  Details  in  Table  1.   

Table  1  :  Unleached  EP  of   Latices  From  Different   Sources 

     *  All  latices  were  compounded  into  normal  2  parts  compound  and  EP  were  tested  with  

        RRIM-Modified  Lowry  Method.

This  makes  process  control  more  difficult  and  thus  affects  the  consistency  of  EP  and AP in  gloves  from  time  to  time.

 3.   LOW PROTEIN LATEX PROPERTIES - LOPROTEX  LPX

Table  2   shows  the  typical colloidal properties   of  LOPROTEX  LPX. These properties are closely resembling those of normal latex concentrates except for the much lower non-rubber content and higher MST.

Table 3 ( a ) shows  protein contents of  LOPROTEX  LPX.   The  leached  rubber  products  produced from  this  latex  give  excellent  results  in  EP  and  AP  of   50ppm  and   3.5ppm  maximum  respectively.

Table  2  :  LOPROTEX  LPX  Latex  Colloidal  Properties

Table  3 ( a )  :  LOPROTEX  LPX   Protein Contents

* EP  result  without  leaching  processes.

  Recommended  leaching  process  is  1 minutes  wet-gel  and  1  minutes  post-cure  leaching.

 Figure 1 shows Antigen Protein identified by Western Blot Assay using Rabbit Sera a ASTM AL. There is a distinct band at 45kDa and 24kDa whereas those of 14kDa and below are some what degraded giving a smear image. Total Protein using Lowry protein asssay gives Total Protein in the range of 1524 mg/ ml to 3303 mg/ ml. This represent about 10-15% of Total Protein in normal HA concentrate which was reported to be 16 000 mg/ ml to 26 000 mg/ ml. Further Protein analysis on heat cure cast film using ASTM D5712-99 for EP and ASTM D6499-00 for AP ( Antigenic Protein ) gave very low EP and AP as shown in table 3 ( b ).

FIGURE 1 – ANTIGEN PROTEIN IDENTIFIED BY WESTERN BLOT ASSAY USING

                      RABBIT SERA a ASTM AL.

1.                                       MARKER

2.                                       ASTM AL 100μg

3., 4., 5., 6., 7. & 8.              LOPROTEX LPX

9.                                                                               GIVUL LP2

10.                                                                           GICOM 1014 (BASED ON LPX)

Table 3 ( b ) : Extractable and Antigenic Protein Content of Unvulcanised Heatcure Cast films.

(Duplicate Determination)

 4.  COMPARATIVE STUDY OF EP AND AP OF COMMERCIALLY AVAILABLE

     LATEX PRODUCTS AND SIMILAR ARTICLES MADE FROM LOPROTEX LPX

     Commercial samples of examination gloves, surgical gloves, household gloves, balloons,

 prophylactics, rubber threads, finger cots, catheters and soothers were collected for EP, AP

 and Nitrogen study. Table 4, 5, 6 and 7 show details of these samples.

 3 batches of Loprotex LPX, each compounded into 2 parts compound as well as prevulcanised

 latex were used to produce similar latex articles for comparative studies with those of

 commercial samples.  Results obtained are as shown in Table 9.

  These commercial samples, as well as articles made from Loprotex lattices were tested for

  Tensile, Modulus and Elongation at Break.  Results are shown in Table 10.

Table  7  :  Average AP of Various Commercial Latex Products Available in the Market

Table  8 : Average Total Nitrogen of Various Commercial Latex Products Available In The 

                 Market

*  <DL  -  below  detectable  limit means < 10  mg/ g.

*  (     )  - repeat result

Table 10 : Physical Properties Of Commercially Available Latex Products In Comparison     

                With Those Of Loprotex LPX Products

5.   RESULTS AND DISCUSSION

i.     For Powder Exam Gloves, 66% with EP >250ppm and AP >20ppm , 17% with EP between

       100-250ppm and AP between 10-20ppm and 17% with EP <50ppm and AP <10ppm.

  For Powder Free Exam Gloves 33% with EP between 50-100ppm and 67% with EP 

  <50ppm.  All gloves have AP <10ppm.

ii.    For Powder Surgical Gloves, 50% with EP between 100-250ppm and 33% with AP >20ppm;

while 17% with EP between 50-100ppm and 33% with EP <50ppm and 67% with AP

<10ppm.

 For Powder Free Surgical Gloves 50% with EP between 50-100ppm and 50% with EP

 <50ppm and 100% with AP <10ppm.

iii.  From  ( i ) and ( ii ) above, we found that for both Powder Examination and Powder Surgical Gloves, the EP and AP results are in wider range.  The best gloves give very low EP and AP of 15ppm and AP of 0.7ppm respectively.  On the other extreme, the EP is at the high of 346ppm with AP of 56.9ppm. For Powder Free Examination and Powder Free Surgical Gloves, the results are more consistent. Maximum EP is 66ppm and maximum AP is 7.6ppm. The minimum EP is below detection limit and minimum AP is 0.5ppm.

iv.  The results also showed that at EP exceeding 100ppm, there is  no good  correlation  between   EP  and  AP.    However  at  EP  of  below  100ppm,  a  lower  EP readings will give lower AP.  At EP of 50ppm and below, the AP results will be less than 5ppm. 

v.   For Household Gloves, 33% with EP between 50-100ppm and AP >20ppm while 67% with

      EP <50ppm and AP <10ppm.

vi.   For Balloons, 33% with EP >250ppm and AP between 10-20ppm; 67% with EP <50ppm and

       AP <10ppm.

vii.  For Condoms, 17% with EP between 50-100ppm and 17% with AP >20ppm and 17% with

       AP between 10-20ppm while 83% with EP <50ppm and 67% with AP <10ppm.

viii. For Finger Cots, 100% with EP <50ppm and AP <10ppm.

ix.   For Catheters, 100% with EP <50ppm and AP <10ppm

xi.   For Soothers, 20% with EP between 50-100ppm and 80% with EP <50ppm while 100%

       with AP <10ppm.

xii.  For Rubber Thread, 38% with EP >250ppm and 0% with AP >20ppm, 25% with EP

between 100-250ppm and 13% with AP between 10-20ppm and 25% EP between 50-   

100ppm while 50% with EP <50ppm and 87% with AP <10ppm.

xiii. From the above results, we can infer that unless the gloves are subjected to post treatment  

       and good leaching, like in the production of Powder Free Gloves and Catheters, the EP and  

       AP are not consistently at low  level.  

xiv. From Table 9,  EP  and  AP  of  leached  and unleached Examination/Surgical Gloves, 

       produced from Loprotex LPX, are very consistent with unleach EP at maximum 87ppm and