Stress relaxation measurement of rubber in tension—A new technique

The purpose of this study was to gain a clearer picture of the structure and properties of vulcanized films made with skim and cream latex from Hevea brasiliensis. The two properties targeted for this study were the elasticity of the films and their permeability to acetone. Surface characterization by atomic force microscopy revealed that vulcanization substantially modified the structure of the films compared to unvulcanized films. Unlike unvulcanized films, particle identity was retained in the vulcanized films made with cream latex, even after 4 weeks of aging. In addition, skim latex gave vulcanized films with greater elasticity than those obtained with cream latex. On the basis of the structural characterization carried out on the latex and films and information from the literature, the greater elasticity of the skim films arose from more entanglements between polyisoprene chains and associations between proteins. Despite differences in the structure, the acetone permeability was very similar for skim and cream vulcanized films.

Section: Mechanical Properties and Elasticitymentioning

confidence: 97%

Comparative study of the elasticity and permeability of vulcanized films made with skim and cream natural rubber latex

Winsunthorn

Bonfils

Pochat-Bohatier³

et al. 2008

“…9 Among these, amino acids or proteins have been identified and it is believed that they are responsible for storage hardening and formation of microgels. Elimination of these constituents might reduce side reactions during chemical modification of the NR.…”

Section: Pnr Analysismentioning

confidence: 99%

Kinetics and parameters affecting degradation of purified natural rubber

Phetphaisit

Phinyocheep

2003

Purified natural rubber (PNR) was obtained by treatment of high ammonia NR latex with proteinase enzyme for 24 h, followed by double centrifugation. The PNR was later redispersed into latex form with 0.5% (w/v) sodium dodecyl sulfate. The degradation of PNR was performed in latex form by using a combination of the radical initiator potassium persulfate (K 2 S 2 O 8 ) and propanal. The intrinsic viscosity [] of the degraded rubber or liquid rubber that was obtained depended on various parameters such as the initiator concentration, amount of propanal, dry rubber content, reaction time, and temperature. It was found that the [] of the rubber can be reduced from 4.31 to 0.19 for the PNR after a 25-h reaction time using 5% dry rubber content PNR latex, 1 part per hundred rubber (phr) of K 2 S 2 O 8 , and 32 phr of propanal at 80°C. The kinetics of the degradation reaction were investigated. The highest rate constant found was 11.33 ϫ 10 Ϫ2 s Ϫ1. The activation energy of the degradation reaction was 76.56 kJ mol Ϫ1 .

“…During this process, the NR structure evolves to produce gel which increases over the sample storage time 6–8. Many studies have been undertaken to identify mechanisms and natural compounds of latex involved in NR hardening during storage,9–16 but to our knowledge, no studies have been published about changes in NR macromolecular structure during storage. Several compounds of latex involved in crosslinking reactions have been proposed: amino acids,9, 11 inorganic ions (Mg 2+ , Ca 2+ ),13 proteins,16–19 phospholipids 15.…”

Section: Introductionmentioning

confidence: 99%

“…Many studies have been undertaken to identify mechanisms and natural compounds of latex involved in NR hardening during storage,9–16 but to our knowledge, no studies have been published about changes in NR macromolecular structure during storage. Several compounds of latex involved in crosslinking reactions have been proposed: amino acids,9, 11 inorganic ions (Mg 2+ , Ca 2+ ),13 proteins,16–19 phospholipids 15. These compounds react with so‐called abnormal groups on the polyisoprene chains, such as carbonyl and aldehyde groups,9, 20 epoxide groups,10, 21 lactone,22 and phospholipids,15 to produce gel.…”

Section: Introductionmentioning

confidence: 99%

SEC‐MALS study of dynamic structuring of natural rubber: Comparative study of two Hevea brasiliensis genotypes

Wisunthorn

Liengprayoon

Vaysse

et al. 2011

ABSTRACT:The dynamic structuring of natural rubber (NR) was studied selecting two specific Hevea brasiliensis genotypes (RRIM600 and PB235) to prepare model samples. The mesostructure (macromolecular structure þ aggregates or gel) of NR samples was studied by SEC-MALS. The NR samples were analyzed after (i) slow structuring (18 months' storage at room temperature) and (ii) fast structuring (stored for 24 h on P 2 O 5 at 60 C). This study showed that the macromolecular structure, especially M n , and the total gel rates were dramatically modified after fast structuring. For genotype RRIM600, the aggregates formed during fast structuring were essentially macroaggregates, whereas for genotype PB235 mostly microaggregates were formed. These results indicate that the dynamic structuring of NR is dependent on genotype. Depending on the genotype, for extreme conditions (fast structuring), it can be assumed there was percolation between elementary bricks, probably microaggregates, or no percolation. Although the mechanisms of dynamic structuring are quite complex and should be multifactors dependent, on the basis of our results, the degree of percolation seems to be partly dependent on the quantity of short polyisoprene chains initially present in the NR samples.