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RUBBER COMPOUNDING PST 333

EXPERIMENT 2: EFFECT OF DIFFERENT TYPES OF VALCANIZATION SYSTEMS

Name of Group member: 1) 2) 3) 4)

MUHAMMAD NUAIM AKIFF BIN AZHA (2019263042) MUHAMMAD AMIRUL ADDLI BIN SHAMSUDIN (2019226256) MUHAMMAD ASYRAF BIN MOHD FADHLI (2019430984) MUHAMMAD FARIS BIN SHAMSHUL KAMAL (2019445106)

Name of Lecturer incharge: DR NURUL AIZAN BINTI MOHD ZAINI

Date of submission: 8/6/2021

EXPERIMENT 2: EFFECT OF DIFFERENT TYPES OF VALCANIZATION SYSTEMS INTRODUCTION 1. Vulcanization is a chemical process in which long rubber chains are chemically connected to an elastic network that heats the rubber at 140–160°C with sulphur, accelerator, and activator. Therefore, the atomic bridges consisting of the sulphur or carbon-to-carbon bonds join each other loosely each rubber chain modules. 2. The vulcanizing agent is a chemical reaction that is generally caused by heat between rubber and a functional group. The outcome is a product stronger, more elastic, more durable, less sensitive than the original polymer to variations of temperature and the effect of solvents. Inorganic basic materials were the first accelerators employed. The fundamental plum carbonate, lime, magnesia, and leather. For many years, inorganic accelerators have been the leading kind. Today they have mainly been replaced by organic accelerators since they are stronger and generate more resilient, quality and durability vulcanizations. 3. Vulcanizing sulphur can be divided into two broad categories: undeveloped sulphur and rapid vulcanization of sulphur. The unchanged formulas are usually sulphur, zinc oxide, fatty acids like stearic acid, and an accelerator in the system is included in the accelerated formulas. Sulphur-free systems, sometimes called sulphur collector systems, constitute a subclass of rapid sulphur vulcanization. The accelerator, acting both as an accelerator and as a sulphur donor, provides the sulphur required in these systems for the formation of the network. 4. Rubber cross links with curing chemicals other than sulphur may also be made: 

Peroxides heal by breaking down into peroxide radicals, which steal an elastomer's hydrogen and produce a radical polymer. Most of the radicals create cross-links instantly. Peroxides give the benefit of saturated and unsaturated rubber curing and create very thermally stable carbon crosslinks. But peroxide curing does have certain downsides; certain antioxidants cannot be utilised due to weak tensile and tear strengths, and the cost is greater than sulphur vulcanization.



Magnesium oxide is used to cure polychloroprene by converting its very few active allylic chlorides to ether cross-links, from a 1 or 2 addition. The combination of t-butyl phenolic resins in solvent-borne polychloroprene adhesive has a synergistic effect. There is a synergistic impact. The

phenolic group in the resin reacts to cross-link magnesium oxide when the solvent is removed. 

Resins of phenol formaldehyde. These are employed for thermally stable carbon-carbon linkages in the formation of butyl rubber.



p-Benzoquinone dioxide. It is also utilised for the treatment of butyl and other unsaturated resins following the same method as for resins of phenol-formaldehyde. Benzoquinone treatment requires the conjunction of a benzo thiazyl disulphide or an inorganic oxidant (lead oxide). At room temperature this mechanism is operational.

5. A) Conventional vulcanization (CV) system 

It includes high sulphur levels (2.0-3.5 phr) It has small accelerator ratios (0.4-1.2 pphr). Accelerator sulphur >1.0 ratio. The network will predominantly be thermally unstable polysulphid (over 65 percent). Excellent mechanical strength, low setting and resilience to heat and ageing.

B) Efficient vulcanization (EV) system 

Small sulphur (0.4- 0.8 phr) designed cure systems It has high accelerator proportions (2.0-5.0 pphr)r). Sulfur accelerator ratio is 2.5 to Sulfurulp Efficient utilisation. The network is mostly monosulfide (75%), which is thermally stable. Low set, good heat and ageing strength, somewhat less than traditional mechanical strength.

C) Semi efficient vulcanization system 

The conventional and EV system compromise. A compromise Sulfur is around 1.0-1.7 pphr. Includes intermediate accelerator proportions (1.22.4 phr) Moderate polysulfide crosslink quantities (40%) Significant quantity of monosulfide (35%) with low disulfides (25%) Intermediate properties to those of EV & CV systems.

OBJECTIVE To familiarize student with: a) Types of sulfur vulcanization system b) Influence of types of sulfur crosslink on the mechanical properties and heat ageing resistance EQUIPMENTS a) Two-roll mill b) Cutting blade c) Scraper d) Thermometer e) Stopwatch f)

Weighing machine

g) Hardness tester h) Tensile machine i)

Curemeter

j)

Mooney viscometer

k) Compression moulds l)

Hot press

FORMULATIONS Ingredients/ Mix Number

1(pphr)

2(pphr)

3(pphr)

4(pphr)

Natural Rubber (SMR 10)

100

100

100

-

Styrene butadiene rubber (SBR)

-

-

-

100

Zinc oxide

5

5

5

5

Stearic acid

2

2

2

1.5

Antioxidant (TMQ)

1

1

1

1

Sulfur

3

1

2

3

Accelerator - MBTS

1

3

2

1

PROCEDURE 5.1 Weighing the rubber and compounding ingredients : An electrical weighing balance is used to accurately weigh each ingredient. Different cup is used for each ingredient and was labelled in accord to the mix number. The rubber is cut into a small blocks using a rubber cutter.

5.2 Preparation of rubber mixers : Through the nips of the mill the waster rubber is passed by to warm up the 2-roll mill. The rubber passed it by few times until it formed a band on the surface of the mill. The rubber is cut and folded a few times and the rubber was removed. The temperature was recorded of the front of the surface of the roll. The mill is cleaned before the mixing started. The mixes is prepared by the following mixing sequences : a) The rubber is premasticate until it forms a relatively smooth band on the front roll. The nip size of the mill is adjusted until it find a suitable bank size form in top of the rubber band. b) Zinc Oxide is added a little at a time until it is incorporated into a bulk of the rubber. The rubber band was cut and the bad was folded either to the left or right. To improve the dispersions and homogenization, the cutting and the folding continued for few times (4-5 times). c) Steric Acids is added a little at a time. The rubber band will tear apart and causes problems during the mixing process since the rubber is tend to be slippery if the steric acids was not added during the mixing sequences. The cutting and folding was applied for a few times. d) The antioxidant and the accelerator was added. The cutting and folding was applied for few times. e) The sulphur is added and the cutting and folding was applied for few times. f)

The rubber band was rolled and passed end-wise for few times to ensure the dispersions and the homogenization of the sulphur.

g) Lastly, about 4mm thick mix is sheet out. The rubber mix was cooled and the mix was labelled.

5.3 Determination of the rheological properties. 5.3.1 Mooney Viscosity. By using a Mooney viscometer at 100◦C, the Mooney viscosity of each rubber mix is determined. 24g sample is used for this test. The work began after the procedures was read. The Mooney Viscosity is recorded at Mooney Viscosity value Mʟ (1+4), 100◦C.

5.3.2 Cure Characteristics. The cure characteristics of each rubber was determined by using an oscillation disc Rheometer at 140◦C and 180◦C. 10g samples is used for each rubber mix. The maximum torque, minimum torque and the scorch time t₉₅. The cure curve of this test is reversion.

5.4 Moulding. The test pieces desired is prepared by choosing the correct moulds. The compression moulds is used for this case to prepare the rubber sheet for the dumbbell test-pieces and prepared for the hardness discs. The mould cavity was cleaned by using a suitable solvent. All dirt and rubber contamination is removed. The electrical press is set to the desired curing temperature (first moulding at 140◦C and the second one sitting at 180◦C ). The mould is preheated for 30 minutes at the vulcanization temperature. The temperature of the mould is checked before the moulding. During moulding, the correct mould pressure is applied. The blank weigh is prepared for each moulding. The rubber plank is placed into the mould cavity when it is ready and closed the mould in the press. The curing take place to its optimum cure time .The cured sample is removed from the mould after the completion, the sample is labelled.

-5.5 Physical Testing. 5.5.1 Tensile properties. Five dumbbell test pieces from the vulcanized rubber sheet is prepared. The thickness is measured by using a thickness gauge and the mean value is recorded. The stress strain measurement is carried out by using a tensile machine at the crosshead speed 500mm per

minute at 23◦C. The computed data, the tensile strength and the elongation at break is recorded.

5.5.2 Hardness. The hardness test is conducted by using the hardness indenter dead-load tester. The mean value is recorded.

DATA

TYPE OF VULCANIZATION SYSTEM CURE CHARACTERISTICS

MINIMUN TORQUE, ML (dN.M) MAXIMUM TORQUE, MH (dN.M) SCORCH TIME, ts2 (min) OPTIMUM CURE TIME, tc90 (min)

CV

SEMI-EV

EV

0.16 7.2 3.89 8.82

0.14 6.09 3.54 6.92

0.13 5.7 3.16 5.62

TABLE 2.2: CURE CHARACTERISTICS OF NR COMPOUNDS

RESULT

RESULT OF EACH OF THE VULCANIZING SYSTEMS 10 9 8 7 6 5 4 3 2 1 0

IN M

UN IM

TO

8.82 7.2

6.92 6.09 5.7

5.62 3.89 3.54 3.16

0.16 0.14 0.13

U RQ

M E,

L

M N. (d

)

AX M

UM IM

TO

U RQ

M E,

H

) M N. d ( CH OR C S

T

E, IM

ts

2

(m

) in

O

CV

SEMI-EV

I PT

UM M

R CU

E

E, M TI

90 tc

(m

) in

EV

DATA

MECHANICAL/PHYSICAL

TYPES OF VULCANIZATION SYSTEMS

PROPERTIES CV SYSTEM

SEMI-EV

EV

TENSILE STRENGTH (MPa) ELONGATION AT BREAK (%) STRESS AT 100%

24.84 1005.1 0.8

18.99 929 0.67

15.78 904.98 0.59

ELONGATION (M100) HARDNESS (IRHD)

52

48

42

TABLE 2.3: EFFECT OF DIFFERENT VULCANIZING SYSTEMS ON TENSILE PROPERTIES AND HARDNESS OF NR COMPOUNDS

RESULT

DISCUSSION 1) The observed difference because the vulcanizing ingredient such as accelerator and sulfur. 2) i) Curing system provides the highest scorch safety (ts2) is CV because the compound has started the curing prosses. ii) Curing system provides the highest optimum cure time (tc90) is CV because the compound has obtain a optimum curing time prosses.

3)

5) The effect of different curing systems on the tensile strength, elongation at break, modulus at 100% elongation and hardness of NR compounds is CV undercure-give higher polysulphides levels and Low temperature vulcanization gives higher proportion of polysulphidic crosslinks than monosulphidic. 6) Polysulphidic is a crosslink in which two rubber chains are bridged by a chain of 3 or more sulphur atoms. It also weak and labile crosslinks, not thermally stable and highly influence on mechanical properties. Polysulphidic is the bond energy of this crosslink is less than 268 kJ/mol (relatively low). Monosulphidic is a crosslink in which two rubber chains are bridged by a chain of one sulphur atom. It also thermally stable and highly influence on reversion resistance and ageing. Monosulphidic is the bond energy of this crosslink is about 285 kJ/mol (relatively high). Semi efficient vulcanization system is moderate amount of polysulfidic crosslinks (40%) and appreciable amount of monosulfidic (35%) with little disulphidic (25%). It is Properties intermediate to that of EV & CV systems. 7). i) Enhancing mechanical strength. Ground tire rubber was thermo-mechanical reclaimed at 120 °C using a co-rotating twin screw extruder. The effect of vulcanizing system type on curing characteristics, static mechanical properties (tensile strength, elongation-at-break, hardness and resilience), dynamic mechanical properties and thermal properties of reclaimed ground tire rubber was investigated. Reclaimed rubber was cured using different types of vulcanization accelerators (MBT, TBBS, TMTD, DPG, CBS) commonly used in industry. Two ratios of vulcanization accelerator/sulfur 2:1 as conventional system and 1:2 as effective system (EV) were used. Presented results indicate that static and dynamic mechanical properties of revulcanized reclaimed rubber depend strongly on vulcanizing system type. The highest cross-link density showed samples cured with TMTD which corresponds to ΔM values, glass transition temperature and equilibrium swelling degree of these products. The best processing and mechanical properties were estimated for revulcanized reclaimed rubber cured with conventional vulcanizing system based on TBBS and CBS accelerators. These results showed that reclaimed rubber obtained via low temperature extrusion is suitable for application in rubber compounds. ii) Improving the heat aging resistance. Sulfur was added into polybutadiene rubber/nature rubber (BR/NR) blends for improving the resistance of thermal aging. BR/NR blends with sulfur were vulcanized by 60Co γ radiation

with different irradiation doses. Afterwards, the specimens underwent thermal aging by using air oven, the non-aged specimens without such process. It was found that the crosslink degree of BR/NR blends increased with the increase in the irradiation dose, according to the results of gel and molecular weight between crosslinks (Mc). Furthermore, the crosslink degree of BR/NR blends increased after thermal aging. This made the mechanical properties and initial degradation temperature (IDT) of aged BR/NR blends improve. Sulfur could improve thermal resistance of γ-irradiated BR/NR blends.

radiation vulcanization is considered as an alternative method for improving the resistance of thermal aging .Carbon-carbon (C-C) crosslinks instead of carbon-sulfur (C-S) crosslinks form during radiation vulcanization process .The bond energy of C-C and C-S bond is 85 kcal/mol and 64 kcal/mol, respectively .Therefore, the radiation-vulcanized rubber provides high stability and good mechanical and thermal properties .Furthermore, radiation vulcanization has many advantages including operating at the room temperature, consuming less energy, being faster, and inherently clean technology .It is a simple and an eco-friendly process, which has already been commercialized. the effects of sulfur on the thermal aging of irradiation-vulcanized BR/NR blends with different doses. Two groups of irradiation-vulcanized BR/NR blends were prepared; the aged one is with thermal aging, while the non-aged one is without such process. From the mechanical strength data, the aged BR/NR blends had higher tensile strength than that of non-aged ones, which contributed to the higher crosslink degree. The thermal aging could promote the new crosslink points form. CONCLUSION Depending on the cure system's ob ectives, zinc oxide or magnesium oxide, stearic acid or other fatty acids, or its metal salts are required to activate the curing reaction using accelerators in sulfur cure systems. A high accelerator to sulfur ratio, known as efficient vulcanization (EV), is used to improve aging resistance. This system produces more monosulfidic crosslinks, which are less flexible than polysulfidic crosslinks and thus have lower dynamic properties. The traditional cure system, with a high sulfur to accelerator ratio, produces more polysulfidic crosslinks and thus better dynamic fatique properties. It is the compounder's responsibility to determine which sulfur cure system will provide him with the best properties for the end use product.

Curing, also known as vulcanization, causes the long polymer chains that make up rubber to crosslink. This prevents the chains from moving independently, allowing the material to stretch when stressed and then return to its original shape when the stress is removed. The type of sulphur cure system suitable for enhancing mechanical strength is Conventional vulcanization (CV) system because higher of sulfur meanwhile Efficient vulcanization (EV) system has smaller amount of sulfur. The type of sulphur cure system suitable for improving the heat aging resistance is Efficient vulcanization (EV) system because it contains high proportion of accelerator meanwhile Conventional vulcanization (CV) system contain lower proportion of accelerator.

REFERENCE 1. Lab Manual PST 333 2. Lecture Notes By Dr Nurul Aizan Bt Mohd Zaini :Lecture Notes Chapter 3: Valcanization 3. Chemistry, Manufacture and Applications of Natural Rubber, 2014 4. JOSÉ MIGUEL MARTÍN-MARTÍNEZ, in Adhesion Science and Engineering, 2002 5. Nicholas P. Cheremisinoff Ph.D., in Condensed Encyclopedia of Polymer Engineering Terms, 2001...