BLOOM & PSUEDO-BLOOM

 

 

BLOOM

 

Since most rubber chemicals are more polar than NR/SBR/BR/EPDM, when dosage exceeds the limits given in the table, they do dissolve at higher temperatures during processing forming a super-saturated solution, but on cooling down especially with some nucleation such as touching, scratching or plain dust settling on final mixes, these chemicals will bloom out.  Some chemicals like TMTD, stearic acid/zinc stearate gives an off-white matt bloom whilst others form crystals which spackles under sunlight such as sulphur.  The spectacular bloom is given by PVI crystals (hexagonal) – hence the common expression “ sparkling fever”.

 

Bloom in uncured final mixes leads to cosmetic problems in cured products such as yellow pips and these pips are a source of failure – hot tearing or product tearing or cracking during service.

 

Similar blooms can also occur with cured products due to “undercure” even though fresh compounds did not exhibit bloom because of their fast turn-over.

 

Stearic acid/zinc stearate bloom usually occurs due to excessive use of zinc stearate as an anti-tack agent.

 

 

PSUEDO-BLOOMS

 

Although such-artificial blooms can include effects of sunlight, artificial light and ozone crazing, most common causes are mechanical fracture of aggregrates of undispersed material like :

 

                        CaCO3

                        Clay

                        MBT mini-pellets

                        MBTS mini-pellets

                        Etc.

 

The most common psuedo-bloom is the use of coarse ground CaCO3 ex. Mesh # 325 in loadings more than 70 PHR.  At excessive loadings, some of these CaCO3 aggregates at the surface are not fully polymer encapsulated.  During mould stripping, under strain, the CaCO3 aggregates fracture and leave a trail of loose CaCO3 particles.  The same effect can be see by striking a highly CaCO3 filled car mat with an iron rod.  Such blooms are psuedo-blooms.

 

 

UPPER LIMIT OF RUBBER CURATIVES SOLUBILITY

 

 

Solubility of rubber chemicals are affected by factors such as filler content, oil, other additives and treatment of final mixes.  In general, the higher the filler or oil content, the higher the solubility.  Data below refers to ambient temperatures, as solubility of most rubber chemicals increases with temperature, example S is soluble in NR or SBR up to ~ 1.2 PHR at 25oC but at 93oC solubility of S increases to ~ 8 PHR.

 

Based on common formulations.

 

                                                                                    Solubility in NR, SBR, BR or EPDM

                                                                                    Compounds. Max. PHR

S                      ----------------------------------------            1.5

MBT                ----------------------------------------            3.0

MBTS              ----------------------------------------            3.0

TMTD             ----------------------------------------            0.5

TMTM             ----------------------------------------            0.7

CBS                 ----------------------------------------            2.5

TBBS               ----------------------------------------            2.5

ZDEC              ----------------------------------------            0.8

ZDBC              ----------------------------------------            2.0

PVI/CTP          ----------------------------------------            0.5

Stearic Acid     ----------------------------------------            2.0

 

                                                                                    Solubility in NBR

TMTD             ----------------------------------------            2.0 – 3.0

TMTM             ----------------------------------------            2.0 – 3.0

 

 

SOLUBILITY PARAMETERS OF POLYMERS

 

                                                           

 

d

(Cal cm-3)˝

FKM

6

Q

7.3-7.6

EPDM

7.9

PE/PP

8.0

PIB

8.0

Polyethylene PE

8.0

BR

8.1

NR

8.4

SBR

8.4

PS

8.7

Thiokol

9.2

CR

9.3

ACM

9.4

Amino Resins

9.6-10.1

Epoxy Resins

9.7-10.9

PVC

11.0

Nylons

12.5-13.6

NBR

14.0

Increasing

Polarity

 

 

 


      

                                                           

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Solubility Of Some Solvents

 

 

 

d

(Cal cm-3)˝

n-hexane

7.3

Diethyl ether

7.4

Paraffin

7.5

n-octane

7.6

Aromatic Oils

8.1

Cyclohexane

8.2

Methyl-n-butyl ketone

8.6

Pine Oil

8.6

Carbon tetrachloride

8.6

Xylene

8.8

Toluene

8.9

Dioctyl phthalate

8.9

Ethyl acetate

9.1

Benzene

9.2

Chloroform

9.3

Trichloro ethylene

9.3

Carbon disulphide

10.0

Acetone

10.0

Isopropanol

11.5

Acetic Acid

12.6

Ethanol

12.7

Methanol

14.5

Ethylene Glycol

15.7

Glycerol

16.5

Water

23.4

Increasing

Polarity

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Note:  Solubility Parameter d is given viz:

 

 

 

 

          Where    L = latent heat of evaporation

   R = gas constant

   T = absolute temperature

   M = molecular weight

   D = density

 

 

= cohesive energy density

 

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Last Modified 19/01/00