Slide cao su hóa học và công nghệ chemistry of accelerated sulfur vulcanization

CHEMISTRY OF ACCELERATED SULFUR VULCANIZATION cuu duong than cong... CuuDuongThanCong.com https://fb.com/tailieudientucnttcuu duong than cong... Formation of MBTS from MBScuu duong than

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CHEMISTRY OF ACCELERATED SULFUR

VULCANIZATION

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B CROSSLINKING CHEMISTRY

• Formation of crosslink precursors

• Conversion of crosslink precursors to

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• (a) sulfur crosslinks (y=1 mono, y=2 di, y>2 polysulfide crosslinks

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A- ACCELERATOR CHEMISTRY

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Formation of MBTS from MBS

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Reaction of sulfur with MBTS and other Accelerator-polysulfides

A key intermediate that reacts with

elemental sulfur is MBTS

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Exchange reaction among accelerator polysulfide

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Effect of ZnO-Formation of

Zinc-Accelerator Complexes

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Zinc-accelerator complexes may also

undergo exchange reactions with other accelerator complexes to yield a distribution

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B- Crosslink chemistry

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Formation of crosslink precursors

• Crosslink precursors are formed when the accelerator polysulfides react with the

rubber chains, resulting in structures

RSX-SBt

• If Zinc is complexed to the accelerator

polysulfide, the crosslink precursors can

be BtS-Zn-SXSBt

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Conversion of crosslink precursors

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The Zinc chelation can stabilize other sulfur bonds Thus, in the presence of Zinc many of S-S bonds can break

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R-SY* can react with an allylic carbon on a parent chain to form a crosslink

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Scorch delay reaction

two different explanation have been

proposed to account for scorch delay:

-Thermal stability of the accelerator

- Exchange reaction between derived intrmediates

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C-POST-CROSSLINKING CHEMISTRY

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Crosslink desulfuration and

main-chain-modification

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The degradation of the polysulfide

crosslink RSYR is more likely to proceed via the radical RSX* and RSZ* than RSY* and R* (S-S bond is more easily broken than

C-S bond)

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RETARDER CHEMISTRY

• Increasing in scorch delay can be achieved

by adding small amounts (0.1-o.4 phr) of

a retarder (pre-vulcanization inhibitor, PVI)

• A typical PVI has an R-S-N group, where R does not contain the proton acceptor site common to the accelerator species

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• A common industrial PVI is

N-(cyclohexylthio)pthalimide (CTP)

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• The rate of this reaction is faster than the rate at which MBT reacts with MBS to form MBTS.

• MBTS formation is delayed and as a

consequence crosslink formation is also

delayed

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MBS MBT + Amine

MBS + MBT MBTS + AmineCTP + MBT CDB + PhtalimideFast

Slow

Định dạng
Số trang	36
Dung lượng	4 MB