properties of high impact polystyrene
28 Feb
Uncategorized

The most important physical and mechanical properties of high impact polystyrene (HIPS)

What do you know about the properties of high impact polystyrene ? High Impact Polystyrene, abbreviated as HIPS, is a type of impact-resistant plastic used in the manufacture of home appliances and utensils. It is very suitable for wet places due to its durability. This plastic is available in the market in terms of weight, flexibility, lightness, and reasonable price, and due to its extraordinary properties, this product is used in most industries.

High Impact Polystyrene, commonly known as HIPS, is a generic version of polystyrene rubber. The addition of rubber makes the thermoplastic extremely durable and has a much higher strength than its previous composition. Like all thermoplastics, it becomes soft and pliable when heated and solidifies again when cooled. These factors alone make HIPS an excellent material for parts production.

HIPS has various properties that allow a wide range of thermoplastic applications. With more rubber content, this material can easily go through production processes such as vacuum formation and can easily bend and mold while maintaining its durability.

After re-molding, its properties do not weaken. As a result, it becomes a widely used product. Due to its amorphous properties, HIPS can be painted, so it is great for design purposes that require beautiful beauty.

Due to its wide thermoplastic properties, there are many different applications of high-impact polystyrene (HIPS). Thermoplastic is ideal for marketing purposes due to its strength and durability and is often used for sales displays and advertising signs. It can also be used for thermoforming chambers and car parts, modeling, and plastic toys. In addition, thermoplastics are commonly used to make cabinets and shower enclosures.

High impact polystyrene has great features:

  • Good molding
  • High strength
  • Re-processing
  • Maintain dimensions and temperature
  • Adhesion
  • Printability
  • Paintability
  • Flexibility

Applications of HIPS sheets according to properties of high impact polystyrene

HIPS

HIPS

It can be used in various industries due to its reasonable price and availability. They are used as heat and sound insulation. Among the uses and applications of HIPS, we can mention items such as the production of toys, sports equipment, home appliances, refrigeration insulation in the body of refrigerators and freezers, the manufacture of stencils, sanitary ware, disposable containers, and billboards.

HIPS sheets are one of the 5 basic resins used in electrical applications and construction compounds according to the mentioned characteristics.

These sheets have the following physical and mechanical properties:

Parameter Amount Standard Unit
Tensile strength 300 ASTM D 638 Kg / cm2
Elongation Percentage 65 ASTM D 638 %
Flexural Resistance 350 ASTM D 790 Kg / cm2
Flexural modulus 17500 ASTM D 790 Kg / cm2
Hardness 64 ASTM D 785 L Scale
Impact strength 10 ASTM D 256 Kg.cm/cm
Thermal softening point 97 ASTM D 1525 ºC
Thermal deformation temperature 78 ASTM D 648 ºC
Water absorption 0.05 ASTM D 570 –

According to the above table, the amount of tensile strength is measured by ASTM D638 standard and according to it, its value is 300 (kg / cm2).

Also, Flexural modulus, which is important for us in this table, is obtained from the ASTM D790 standard, which has a value of 17,500 (kg / cm2).

Other properties of high impact polystyrene are also obtained according to the relevant standards and are collected in the table above.

Properties of General Purpose Polystyrene
27 Feb
Uncategorized

Properties of General Purpose Polystyrene (GPPS)

What do you know about Properties of General Purpose Polystyrene ? Today, polystyrene polymer is one of the most widely used polymers in the world after polyethylene. The main advantage of this product, in addition to high transparency, is that it can be easily converted into efficient products by molding. One of the most widely used grades of this material, which is used for general purposes, is General Purpose Polystyrene (GPPS), which is also known as Crystal. Properties of natural polystyrene such as heat resistance, operating temperature, flow and fluidity properties, dielectric and strength properties, and impact resistance of general purpose polystyrene product (GPPS) are optimized. It is widely used to make disposable tableware, electronics such as televisions and radios, sports equipment, toys, and household appliances.

Advantages of general purpose polystyrene (GPPS)

Advantages of general purpose polystyrene (GPPS) include transparency, high rigidity, good dimensional stability, good electrical properties, gamma-ray resistance, and low price. In addition to these advantages, this product also has disadvantages and limitations.

The most important disadvantages are fragility at ambient temperature, poor mechanical properties at temperatures above 70 ° C, high flammability, poor chemical resistance, especially against organic solvents, and sensitivity to ultraviolet radiation.

In the continuation of this article, we will get acquainted with the types of physical, mechanical, thermal, electrical, and chemical properties of general purpose polystyrene (GPPS).

Physical properties of general purpose polystyrene (GPPS)

General purpose polystyrene (GPPS) or crystal is polystyrene with an amorphous and irregular structure that has a shiny glassy appearance. In general, van der Waals bonds (intermolecular forces) play a major role in determining the physical properties of a substance; Therefore, the physical properties of general purpose polystyrene (GPPS) are derived from weak van der Waals bonds between the chains of this polymer.

As the temperature rises, the van der Waals bonds become weaker, causing the molecular chains that make up the material to slide over each other. For this reason, general purpose polystyrene (GPPS) will be very elastic and soft at temperatures higher than the transfer temperature of its glass.

The table below shows the most important physical properties of general purpose polystyrene (GPPS).

Property Unit Amount
Density g/cm3 1.04 – 1.05
Specific density % 1.04 – 1.09
Concentration % 0.1 – 0.7
24 hour water absorption % 0.01 – 0.04
Refractive index % 1.58 – 1.59
Distribution % 88 – 90
Matte amount % 0.1 – 1.1

Mechanical properties of general purpose polystyrene (GPPS)

The mechanical properties of a polymer include properties such as strength, tensile strength, modulus, impact strength, and compressive strength of the material. The crystalline form of general purpose polystyrene (GPPS) polymers shows low impact strength.

General purpose polystyrene (GPPS) polymer is also degraded by exposure to sunlight due to the occurrence of optical oxidation phenomenon and its mechanical properties are affected.

GPPS uses

GPPS uses

The following table shows the mechanical properties of general purpose polystyrene (GPPS).

Property Unit Amount
Tensile modulus or Young’s modulus (elasticity) Mpa 3000 – 3600
Tensile strength Mpa 30 – 60
Tensile strength at the breaking point Mpa 30 – 40
Tensile strength at the yield point Mpa 30 – 40
Elongation at the breaking point % 1 – 5
Increase the length at the yield point % 1 – 5
Strain modulus Mpa 1400
Flexural strength Mpa 76
Flexural modulus Mpa 3200
Tension modulus Mpa 1200
Rockwell Hardness M M65 – M80
Shore D Hardness – 85 – 90

Thermal properties of general purpose polystyrene (GPPS)

Thermal properties include a set of material properties that show up when exposed to heat. Among these properties, we can name the glass transition temperature, thermal conductivity, thermal expansion rate, and so on.

General purpose polystyrene (GPPS) is a hard thermoplastic material that is solid or glassy at normal temperatures and melts as the temperature rises without any chemical change. This substance, when heated above the glass transition temperature of its glass, turns into a liquid phase and flows. In this case, it can be used for molding or extrusion processes.

The values ​​in the table below show the thermal properties of general purpose polystyrene (GPPS).

Property Unit Amount
Lowest operating temperature ° C 20
Highest operating temperature ° C 60
Glass transfer temperature ° C 100
Thermal decomposition temperature ° C 300
Flame temperature ° C 402
Specific heat capacity cal / ° C. g 0.32
Thermal conductivity (at 0 ° C) W / m. K 0.105
Thermal conductivity (between 25 ° C to 100 ° C) W / m. K 0.14
Thermal expansion μm / m. K 120
Softening temperature (wick) ° C 100
Percentage of distribution % 87
Thermal failure temperature ° C 95

Electrical properties of general purpose polystyrene (GPPS)

Electrical properties are the properties that determine the response of a substance to an electric field. The table below shows the values ​​of electrical properties for general purpose polystyrene (GPPS).

Property Unit Amount
Dielectric power MV / m 20
Dielectric constant (In one MHz) 2.5
Volumetric electrical resistance ohm-cm >1016
Arc resistance Sec 70

Chemical properties of general purpose polystyrene (GPPS)

General purpose polystyrene (GPPS) is chemically inert and does not react with many materials, but is soluble in some organic solvents. Many of the chemical properties of general purpose polystyrene (GPPS) are the result of the unique properties of the element carbon.

This product is highly flammable and burns with a yellow-orange flame and, like all aromatic hydrocarbons, produces carbon particles or soot during combustion. In the complete oxidation of general purpose polystyrene (GPPS), only carbon dioxide and water vapor are produced.

properties of expanded polystyrene
25 Feb
Uncategorized

The most important physical and mechanical properties of expanded polystyrene (EPS)

Expanded polystyrene (EPS) is commonly used in various applications in industry and building systems due to its properties such as low weight, thermal conductivity, water and moisture resistance, high durability, sound absorption, and low thermal conductivity. This product is used in building structures as the main material of insulation panels. Some of those structures may be exposed to dynamic loads during their lifetime, such as shocks from wind movement; Therefore, understanding the properties of expanded polystyrene (EPS) is essential to predict the performance of EPS insulation panels.

In this paper, the data of EPS stress and tensile tests such as strength, Young’s modulus, and also the thermal properties of this material such as heat absorption capacity, etc. are presented.

Physical properties of expansion polystyrene (EPS)

A wide range of physical properties of expanded polystyrene (EPS) in combination with engineering considerations makes the process of designing cost-effective food packaging more flexible.

The table below shows the most important physical properties of EPS.

Property The unit                Amount
Density g/cc 0.0031 – 3.5
Fillers % 0.3 – 10.5
Water absorption % 0.03 – 9
Particle size µm 100 – 3150
Water vapor treatment g/m2/day 50 – 200
Viscosity cP 1.65 – 1.7
Permeability to all types of vapors % 0.5 – 3.5
Maximum moisture content % 0.2 – 0.5
Steam pressure bar 0.685

Mechanical properties of expanded polystyrene (EPS)

EPS

EPS

Expanded polystyrene (EPS) has high mechanical strength against pressure; For this reason, it is very suitable for products that need to be put under a lot of pressure. In general, the strength and mechanical properties of this material depend on the particle size and geometry of the molded part, process conditions, and density, and increase with increasing density.

Expanded polystyrene (EPS) has high dimensional stability and retains its appearance properties in different environmental conditions.

The cellular structure of expanded polystyrene (EPS) makes it essentially impermeable to water. However, EPS may absorb moisture when completely immersed in water due to the presence of fine channels in its structure.

Although molded polystyrene is almost impermeable to water, it is relatively permeable to vapor pressure differences. Vapor permeability is a function of the density and thickness of the material, but in general, water and vapor do not affect the mechanical properties of EPS. The basic properties of expanded polystyrene (EPS) foams are largely a function of density. This allows manufacturers to adjust the exact performance required with a simple process change without having to redesign the tool.

The following table shows the values ​​of the mechanical properties of expanded polystyrene (EPS).

Property The unit                Amount
Tensile modulus or Young’s modulus (elasticity) GPa 0.0065 – 2.65
Tensile strength MPa 0.075 – 3
Tensile strength at the fracture point MPa 47.1 – 51
Elongation at the breaking point % 0.124 – 0.3
Creeping strength MPa 0.06 – 0.3
Flexural strength at the breaking point cP 6.9 – 14.1
Tension modulus GPa 0.0019 – 0.004
Impact strength J/cm 0.216 – 0.245
Compressive strength MPa 0.04 – 10.9

Thermal properties of expanded polystyrene (EPS)

The cellular structure of expanded polystyrene (EPS) is closed and 98% of this product is composed of air; Therefore, it is expected that this material has a very low thermal conductivity and can act as a good thermal insulator due to the lack of heat transfer. The thermal conductivity of molded polystyrene can be changed by the density and temperature to which it is exposed.

The values ​​in the table below show the thermal properties of expanded polystyrene (EPS).

Property The unit                Amount
Softness temperature index g/10 min 1.8 – 4
Highest operating temperature °C 70 – 118
Thermal decomposition temperature °C 220
Flash temperature °C -56
Flash temperature °C 285
Flame spread mm/min 1.2 – 136
Thermal conductivity (between 25 ° C to 100 ° C) W/m. K 0.027 – 0.045
Deformation temperature in the short term °C 100
Softening temperature °C 70

Electrical properties of expanded polystyrene (EPS)

The volumetric strength of expanded polystyrene (EPS) molded at 73 ° F and 50% r .h is 4 x 1013. Its dielectric strength is approximately 2 kV / mm. EPS molds can be modified with anti-static agents to meet the standards of the electronics and packaging industry.

Chemical properties of expanded polystyrene (EPS)

Water and aqueous solutions of salts, as well as acids and alkalis, do not affect expansion polystyrene (EPS). Also, most organic solvents are not EPS compliant. Other materials of unknown composition should be tested for compatibility with this material. EPS is generally chemically neutral and resistant to bacterial attacks.

It should also be noted that exposure to expanded polystyrene (EPS) in direct sunlight and ultraviolet rays can cause a yellow color on the surface of the material and make the top layer brittle. Expandable polystyrene (EPS) is flammable but can be modified as a fire retardant to reduce its flammability.

impact strength in high impact polystyrene
24 Feb
Uncategorized

What is impact strength in high impact polystyrene (HIPS)?

By adding 5 to 10% polybutadiene during the polymerization process and creating chemical bonds and forming a double bond of butadiene with some free radicals of polystyrene, a copolymer and a two-phase mixture containing dispersed particles of one phase in another are produced. The final product at the end of this process is impact strength polystyrene, which is resistant to impact and fragility.

This plastic material, more precisely, includes properties such as strength and hardness of polystyrene and flexibility and impact absorption of polybutadiene. For this reason, these polymers are called high impact polystyrene (HIPS).

High impact polystyrene (HIPS) is a product with low fragility and higher impact strength compared to polystyrene. It is used in the manufacture of home appliances or various types of 3D printers due to its high impact resistance.

In this article, we are going to get acquainted with the method of measuring HIPS impact strength and related standards. The impact test is one of the most important mechanical tests to measure the impact resistance of polymers.

Impact test can generally be used in cases such as measuring the material resistance to impact, investigating the effect of temperature on impact strength, examining the degree of sensitivity of materials to the gap (notch), evaluating the characteristics of the cross-sectional area of ​​failure. It is also used to estimate and classify brittle fracture behavior to correctly select materials under specified stress and temperature conditions.

Standard tests to measure impact strength

The impact test is a simple and standard test to identify and measure the tendency of a material to break. Its basis is to determine the amount of energy required to break the part due to impact.

The tester consists of a pendulum that strikes the sample as it moves. The main quantity measured in the impact test is the energy absorbed in the failure of the sample. The difference in pendulum height before and after impact indicates the energy absorbed by the sample, which is usually defined as the energy on the surface.

If the amount of this energy is small, it can be concluded that the material is highly sensitive to impact forces. But if the amount of absorbed energy is high, the material is soft and malleable and can withstand more impact force, and has a higher toughness.

The amount of energy obtained is a measure of the toughness of the material and can be calculated from the difference between the initial and final angle of the pendulum.

The toughness of a material is its resistance to crack propagation or its ability to absorb energy in plastic deformation. This indicates that something can be done without breaking the unit of matter. The material with high toughness has an optimal combination of flexibility and strength.

The most common methods of impact testing are the two methods of Izod and Charpy. In the Izod method, the test sample is placed vertically and in the Charpy method, the test sample is placed horizontally. Also in the Izod test, a slit or notch fixed in a ball pendulum is hit.

While in the Charpy test, the gap is placed away from the impact ball. Another difference is that in the Charpy method, there are two types of gaps (U and V-shaped), while in the Izod method, there is only one type of gap.

Izod and Charpy tests can be applied to a wide range of plastic and composite polymeric materials. Typically, the Izod test is used to measure the strength of polystyrene against impact, which will be discussed below.

The Izod impact strength test

IZOD Test

IZOD Test

As mentioned, the Izod impact strength test is used to measure the impact strength of plastics such as HIPS polystyrene. This is done according to national standard 6981 and ISO 180 and ASTM D256 standards.

The equipment required for the Izod impact test includes a pendulum impact device with suitable support and a micrometer to measure the dimensions of the test and the depth of the gap. The test sample of HIPS can also be prepared by extrusion, compression molding, or injection.

The dimensions of the HIPS sample according to ASTM D256 standard are length 64 mm, width 12.7, and thickness 3 to 12.7 mm. The type of sample slot should also be V-shaped. HIPS samples must have surfaces perpendicular to each other and without twisting.

Surfaces and edges should be free of scratches, cavities, and dents. Samples that do not meet one or more of the requirements for measurement or visual observation should be rejected. Or re-machined to the appropriate size and shape before starting the test. The Izod test usually uses 10 HIPS samples.

In this method, the polymer material is placed vertically in the clamp holding the sample. Now the pendulum goes up to the height specified in the device and is fixed in place. The hammer or pendulum is then dropped to strike the desired location in the sample.

The Izod impact strikes the sample at a certain distance from the closing point of the HIPS sample and in the slotted specimens, at a certain distance from the center of the slit to the sample. The amount of energy absorbed by the HIPS sample is recorded in the device. Sample impact strength is obtained by dividing the recorded energy by the effective surface of the sample.

The effective surface area of ​​the sample is the product of the thickness multiplied by the width of the sample in the non-slit mode. In the case of the slit, the thickness is multiplied by the remaining width behind the slit.

producing expanded polystyrene
23 Feb
Uncategorized

The process of forming and producing expanded polystyrene or EPS

Expanded polystyrene (EPS), also known as ionolite or plastofoam, is a white, lightweight, soundproofing, and moisture-insulating material first used by the Germans in World War II to build bridges. Floating was produced on the water. Expanded polystyrene (EPS) has several applications in packaging and insulation. This product is the most suitable option as an alternative to cement blocks for sound, heat, and cryogenic insulation, and also has many applications in the manufacture of packaging foams and food storage containers. In this article, we will learn more about the forming process and the method of producing expanded polystyrene (EPS) and its features.

Introduction of Expanded Polystyrene (EPS)

Expanded polystyrene, also known as EPS and ionolite and plastofoam for short, is a white, fire-retardant polymer made by combining polystyrene with a foaming agent. Polystyrene belongs to the family of thermoplastics and has a linear chain.

Expanded polystyrene (EPS) is formed by the dehydrogenation of alkylbenzene polystyrene monomers. Due to the release of gas inside this material, the volume of polystyrene grains increases by forty times their original size. After the expansion operation, the expanded grains are molded according to the type of application.

Features of expanded polystyrene (EPS) materials include low thermal conductivity, acoustics and refrigeration, low weight, high impact resistance, fire resistance and fire, and having suitable mechanical properties such as pressure resistance.

In addition, very low heat transfer, low moisture absorption, excellent dimensional stability, insensitivity to water, ability to prevent energy loss, chemical neutrality, and resistance to bacterial attacks.

Investigating the process of producing expanded polystyrene foam (EPS)

EPS Forming

EPS Forming

The initial foaming process:

Initially, the foam formulation components need to be mixed. Shortly after the onset of chemical reactions, the color of the system becomes cloudy and gas bubbles (which are also visible to the naked eye) form. This short time interval from the beginning of mixing to the observation of the cream color in the reaction system is called the creaming time.

As mentioned, due to the short time, the viscosity of the mixed fluids is high and the flow of materials in the mold is poor. Therefore, to produce a uniform foam, the casting process must be performed continuously and uniformly inside the mold. Then, when the gases produced in the liquid system are well dissolved and saturated, the primary nuclei are formed.

Now, the foam is formed, it moves upwards. Simultaneously with the process of production and continuous formation of gas, the produced gas molecules are transferred from the liquid part into the formed cells and nuclei. It should be noted that the smaller the size of these nuclei (cells), the greater the pressure inside them. This causes the smaller cells to become unstable and to merge into adjacent cells larger than themselves. After a while, the total number of cells will decrease and their size and volume will increase.

Also, these cells are spherical at the beginning of formation, but over time, they stretch in the direction of rising foam and become polygonal. The shape of these cells is based on creating the minimum surface area and having the least possible energy.

The process of producing expanded polystyrene foam (EPS) consists of three steps, each of which will be described separately below.

Pre-expansion:

To mold the parts, in the first stage, which is called pre-expansion, it is necessary to prepare the raw puffed material with the necessary density. Polystyrene beads (containing puff-forming agent) prepared during the initial foaming process are fed into a vertical tank equipped with a stirrer.

The tank also has steam, air, and an automatic system for forming expanded grains also called puffs.

By controlling and adjusting the speed of the stirrer as well as the feed rate to the tank (including such as airflow, raw materials, and streamflow), polystyrene granules soften above the boiling point of the blowing agent at about 90 ° C.

The amount of vapor pressure inside these grains also increases. In general, performing this stage of the process will cause the grain to expand and increase in volume and reach the required density.

The minimum density obtained depends on factors such as crop type, initial grain size, puffiness, and the use or non-use of additives. The volume of these grains is increased up to 40 times before the pre-expansion process.

At the end of this stage, these seeds are kept in open containers for some time (up to several hours). This action causes the vacuum created inside these grains to balance with atmospheric pressure in addition to the release of the puffing agent.

After the pressure stabilization step, the initial puffed grains are poured into a closed mold and subjected to steam heating again. At this stage, the primary puffed grains penetrate each other to form a monolithic mold.

If the pre-expansion stage is performed in a discontinuous manner, the polystyrene beads must be pre-weighed and continuously inserted from the end of the pre-expansion tank.

Expanded and puffy seeds should also come out of the upper part. Adjusting and controlling the density of the final products is possible by controlling the pressure and temperature of the pre-expansion tank and the duration of the presence of the grains in the expander.

Finally, the products removed from the pre-expansion tank are transferred to a fluidized bed dryer and then dried.

Initial puff stabilization:

At this stage of producing expanded polystyrene, the raw product removed from the fluidized bed dryer enters large containers to reach normal temperature (close to ambient temperature).

At the same time, which may take three to four days, depending on room temperature, airflow, and density, water vapor around the grains and the residual puffy agent condenses. Also in this process, air can penetrate the grains.

Molding:

At this stage of producing expanded polystyrene, the structure and shape of the molds are determined depending on the type of foam produced and its application. The molds can be made of aluminum, galvanized or ordinary steel, or even wood. If the same mold is used, more materials are used in closed molding processes than in open molding.

Also, the density of the foam increases, and a lot of pressure is created in the mold. Blockchains have six walls that are in contact with the expanding grains. These walls must be covered with Teflon or steel and have a large number of small holes less than one millimeter in diameter to allow steam to enter and air to escape from the mold.

There are three main types of open molds, include complex molds, vacuum molds, and transition molds.

Shaping foams:

This is the final step in producing expanded polystyrene foam (EPS). In addition to the molding process, foams can be transformed into various shapes as desired by combining pressure and cutting. Foam edges can also be formed using the polishing process.

Hardness in HIPS
22 Feb
Uncategorized

Familiarity with various methods of measuring hardness in High Impact polystyrene (HIPS)

Hardness is a key parameter in the manufacture of engineering parts. The hardness of polymers is usually measured by their resistance to hard objects. There are many methods and scales for measuring hardness, such as shore and Rockwell tests. In this article, we will get acquainted with the concept of hardness and its measurement methods and High Impact Polystyrene (HIPS) hardness tests.

What is Hardness?

Hardness is defined as the resistance of a material to the penetration of a needle with standard specifications or a rigid body and surface deformation or scratches. It can indicate the hardness of the top layer or the depth of the material. Due to the penetration of the hard body into the surface of the test sample, three-way stress is created at the pressure site. The resulting deformation is a combination of tensile, compressive, and shear deformations.

Factors affecting the hardness of materials are classified based on their internal characteristics, process, and additives. Influencing factors such as the chemical structure and type of intermolecular bonds, mixing, degree of crystallinity, temperature, humidity, additives (such as fillers), enhancers, emollients, and antioxidants affect the hardness of a substance.

Hardness test methods and tests measure how difficult it is to create an effect on the surface of the part or the degree of penetration of a sharp object into the sample. There is no absolute and uniform criterion for hardness and it can be measured by parameters such as the penetration of the needle under force, abrasion resistance, and abrasion resistance.

Types of standard tests for measuring the hardness of High Impact polystyrene (HIPS)

This test is one of the main and common physical and mechanical tests of materials. Due to the difficult definition presented in the previous section, several standard tests have been defined to measure this property.

In these tests, the general procedure is that a hard penetrating object is pressed against the surface of the test sample based on the geometry of the compressor shape. By applying pressure, creates three-dimensional stress and causes deformation at the surface of the sample. This test is very common and used because of its simplicity and importance.

The most common hardness tests include the Brinell hardness test, the Rockwell hardness test, and the Shore Durometer hardness test. These methods are used for a specific group of materials.

In cases such as the shape of the needle or penetrating body, the material of the needle (steel, hard metal, diamond), the amount and time of loading and applying force, the time of measuring the depression, and the method of measuring the hardness (in terms of penetration depth, recessed area, force) They are different from each other.

The following is a description of the Rockwell and Shore Dorumeter tests used to measure the hardness of High Impact Polystyrene (HIPS).

1- Rockwell Hardness Test

Rockwell hardness test is mainly used for hard plastics such as polycarbonate, nylon, polystyrene, and steel. The standards of this hardness test are ASTM D785 and ISO 2039. The penetrating body in this test is a conical body made of diamond or steel.

First, an initial force is applied to the HIPS sample by the penetrator for 10 seconds and penetrates it to a certain height. Then another force is applied for 15 seconds and penetrates the polymer to a certain height. The Rockwell hardness value is then calculated according to the standard figure.

The three most common Rockwell hardness test methods used in plastics are Rockwell E, Rockwell R, and Rockwell M. Details of these methods can be found in the table below.

Different methods of measuring Rockwell hardness

Method name Apply low load (kg) Apply high load (kg) Bullet diameter (in) Bullet diameter (mm)
R 10 60 0.5 12.7
L 10 60 0.25 6.35
M 10 100 0.25 6.35
E 10 100 0.125 3.175
K 10 150 0.125 3.175

2- Shore Durometer hardness test

The most common method of measuring the hardness of materials is the Shore Durometer method. This method is divided into two different types of Shore A and Shore D, in which a needle in the form of an incomplete cone and a needle in the shape of a cone with a spherical tip play the role of the penetrating body.

Shore Durometer Test

Shore Durometer Test

The Shore A test is used to determine the hardness of soft rubbers and very soft plastics such as softened PVC. Therefore, it is not very useful for measuring the hardness of polystyrenes. The Shore D test is used for the category of hard plastics.

This test is performed according to ASTM D2240 or ISO 868 standards. In both standards, force is applied by weight and spring, and the depth of the depression is a measure of stiffness. One of the advantages of this method is the portability of the test equipment due to the small size of the device.

The equipment required for this test includes a shore tester, equipment support base, HIPS sample, stopwatch, and weights suitable for applying force.

According to the ISO standard, the thickness of the HIPS sample must be at least 4 mm; According to ASTM standard should be at least 6 mm. To measure the hardness of the sample, the HIPS must be placed on the horizontal hard surface of the machine installed for this purpose. The tester is also placed in a vertical position (at least 9 mm away from the edges of the sample).

The compressor base rises quickly but without impact to place the indicator (Shore needle) on the sample and apply sufficient pressure. After 15 seconds, the Shore polymer hardness number can be read. Depending on the technical specifications or the standard of the product, the instantaneous hardness number can also be read 1 second after full contact and creating the appropriate pressure.

To achieve an acceptable amount of stiffness according to this standard, 5 different measurements with a distance of at least 6 mm must be performed and their average reported.

Tensile Strength
21 Feb
Uncategorized

Tensile strength at the breaking point of High Impact polystyrene (HIPS)

Tensile strength is used to evaluate the deformation of High Impact (HIPS) polystyrene and to ensure its quality and hardness. In addition, this test is performed to determine the maximum stress that the material can withstand, as well as the tendency to flexibility and deformability.

The tensile test, which is performed to measure the tensile strength of polymers, is one of the most important and widely used tests of the mechanical properties of polymers. Its results also play an important role in the selection of materials for the production of polymer products.

In general, tensile properties are measured to develop new materials and processes, predict the behavior of a material under various forces, and ensure the quality of polymeric materials and compare them.

In this article, we will talk about the tensile strength of polymers and the tensile test used to measure the tensile strength of High Impact (HIPS) polystyrene polymer material.

Tensile strength

Tensile Strength measurement

Tensile Strength measurement

Stress is a parameter of pressure material is obtained by dividing the force on the effective surface of the sample in the tensile test and the strain is the displacement of the sample relative to the initial state.

As a result of tension, polymeric materials first deform elastically and return to their original state when the stress is removed.

Then, by applying more stress, they deform the plastic, that is, by removing the applied stress, the dimensions of the material do not return to their original state and the deformation and the created state are irreversible. Eventually, with more stress, the material breaks.

Tensile strength is the maximum amount of stress that a polymeric material can withstand during tension and not break. In general, the tensile strength of polymers and plastics is classified into three types and includes tensile strength at the fracture point and final strength.

Tensile strength at the fracture point is the amount of stress that a polymeric material can withstand without permanent deformation and can be measured by a tensile test using a tensile device.

Tensile strength at the breaking point is the amount of material strength at the point where the polymer breaks. The maximum stress that the polymer can withstand is also called the ultimate strength.

In the tensile test, which will be described below, tensile force is applied to the sample body, which is the High Impact Polystyrene (HIPS) sample. The deformation of the sample relative to the initial state and the force diagram are recorded instantaneously (or the stress diagram applied in terms of strain) in the traction device.

The linear part of this curve, which is initially elastic to the point of fracture deformation, is called the elastic region. As mentioned, in this region the relationship between stress and strain is linear. The waxy or plastic region of this curve also begins after the fracture point (the beginning of the deformation of the sample wax). The wax deformation of the sample continues steadily to the apex of the curve or tensile strength.

Many parameters can affect the tensile strength of a polymer. The most important of them are: molecular weight (increasing the molecular weight of polymers increases their tensile strength to saturation point), crosslinking (reducing strength), crystallinity (crystalline phase of the polymer due to stronger intramolecular bonds, Increases strength).

Tensile strength measurement

As explained in the previous section, with the help of the tensile test, the reaction curve of the material against the applied forces can be drawn. In this diagram, the maximum stress (final strength) is very important.

The tensile strength test of High Impact Polystyrene Copolymer (HIPS) is performed according to ASTM D638 standard.

The ASTM D638 tensile test determines the basic mechanical properties of High Impact Polystyrene (HIPS) such as tensile stress, strain, tensile modulus, operating point, breaking point, and Poisson ratio. According to this standard, High Impact polystyrene (HIPS) samples with any thickness up to 14 mm can be used; Therefore, the thickness of materials with more than 14 mm must be reduced by machining to make this method feasible.

In this test, at least 5 samples of High Impact Polystyrene (HIPS) must be tested.

Tensile Strength in HIPS

Tensile Strength in HIPS

The device used in this test is a traction device that has two jaws or clamps. These jaws can generally change depending on the type of sample and its material.

The lower jaw of the device is fixed and is designed to hold the test tube firmly. The upper jaw of the device, in addition to holding the sample in itself, moves upwards and causes tensile stress to the sample.

The initial state of the sample should not be twisted before the test. Samples must be firmly seated between the jaws of the device; So that the jaws themselves do not cause the sample to rupture.

The samples are not very hard, so the jaws are not completely in the same direction, which causes a large error in the test. Therefore, it must be ensured that the jaws are aligned.

After closing the specimens and tightening them and making adjustments on the traction device software, the device is commanded to subject the specimen to the tensile stress at a certain speed (usually set at 50 mm/min). (This speed can vary according to the standard). The sample is pulled by the machine until it breaks.

The software of the device, in which the full dimensions of the sample have already been entered, can calculate and record the tensile strength at the fracture points according to the definitions mentioned in the previous sections.

If the traction device software is not able to measure the tensile strength, the force number from the device at the rupture site (for fracture points) can be divided by the effective cross-sectional area of the sample (multiplied by the thin section of the sample thickness) to obtain strength. In addition, all tensile test parameters can be viewed and measured in the stress-strain diagram.

elongation at the breaking point of High Impact Polystyrene
20 Feb
Uncategorized

What is the elongation at the breaking point of High Impact Polystyrene (HIPS)?

The strength of polymers indicates only the force required to break. This cannot show the changes that occur during the experiment, for example. Therefore, it is necessary to study the behaviors of the polymeric material such as elongation in the sample. Elongation is a kind of deformation in a stressed sample. In this article, we will get acquainted with the concept of elongation as one of the mechanical properties of High Impact Polystyrene (HIPS) and how to measure elongation at the breaking point of High Impact Polystyrene.

What is elongation?

In a tensile strength test to measure the mechanical properties of polymeric materials, including High Impact Polystyrene (HIPS), the polymer sample is deformed by stretching. Then its length is increased, which is called elongation. The percentage increase in length is equal to the length of the sample after being drawn, divided by its initial length multiplied by 100.

The ultimate elongation for each type of polymeric material indicates the amount that the sample can be pulled before its breaking point. Reversible elongation is also the percentage of elongation that can be achieved without permanent deformation of the specimen; This means that after removing the stress, the sample quickly returns to its original length. Measuring this value in elastomeric materials is very important.

Hard plastics in tensile testing do not change much with increasing stress, resizing or strain, and do not deform much. The deformation of these plastics is elastic and they withstand the stress until they fail to the maximum.

Flexible plastics fall into another category. These types of plastics work elastically by applying stress to the deformation area to reach the yield point. After reaching the breaking point, as the amount of stress increases slightly, they change the size to reach the breaking point.

Tensile test

A tensile strength test is a test that puts the sample under a tensile force until it reaches the breaking point. The increase in length is also recorded simultaneously with the force or load applied. The results of this test can be used to control the quality and predict the behavior of a substance under the influence of various forces.

Elongation test

Elongation test

By performing this test, the stress-strain curve of the polymer material, which shows the behavior of the material under tension, can be plotted based on the values ​​of the applied force in terms of elongation.

In most tensile tests, it is observed that in the early stages, there is a linear relationship between the applied force or load and the increase in sample length, and the stress is proportional to the strain.

In this area, the diagram follows Hooke’s law, in which the stress-to-strain ratio is a constant value called the “modulus of elasticity” or “Young’s modulus”.

The modulus of elasticity is a measure of the hardness of a material and applies only to the linear region of the curve. At a point where the curve is no longer linear and deviates from a straight line, Hooke’s law is no longer applicable and permanent deformation occurs in the sample.

This point is called the elastic limit. From this point on, in the tensile test, after increasing the load or force, if the load is removed from the sample, the material will not return to its original condition before applying force.

During the tensile test, the amount of elongation of the sample under the tensile test can be obtained. This value can be obtained by measuring the absolute amount of change in length or a relative measure of change in length, also called strain.

The amount of strain can be expressed in two different ways: engineering strain and real strain. Engineering strain is obtained from the ratio of length change to initial length and is independent of the geometry and shape of the part. The real strain is similar to the engineering strain, except that it is determined based on the instantaneous length of the sample.

How to do a tensile test

The elongation test, also known as the tensile test, can be performed according to ASTM D638 for High Impact Polystyrene Copolymer (HIPS). In this test, at least 5 specimens must be tested and the preferred size of the specimens is a rectangular strip with a width of 10 to 25 mm and a length of at least 150 mm.

The device required for this test is a traction device that has 2 jaws or clamps. These jaws can change depending on the type of test and its material. The initial distance between the clamps or jaws of the device is 100 mm.

Speciman

Speciman

Samples must be secured inside these jaws. The lower jaw of the device is fixed and its job is to hold the specimen firmly. In addition to holding the specimen, the upper jaw of the device moves the specimen by pulling it upwards and applying tensile stress to it.

After closing the specimens and tightening them and making adjustments on the traction device software, the device is commanded to subject the specimen to a certain speed (usually 50 mm / min) with different amounts of tensile stress. The sample is stretched until it fails.

In the end, after the sample reaches the breaking point, the force required to create the elongation is reported and the force curve is plotted accordingly; Because the device software, in which the full dimensions of the sample have already been entered, can calculate the strain and elongation at the breaking point according to the formula.

By performing the necessary calculations, the stress curve in terms of engineering strain can be extracted from the initial curve.

Flexural modulus
19 Feb
Uncategorized

Flexural modulus in High Impact Polystyrene (HIPS) + measurement standard

In many cases in plastics, unlike rubbers, the product should not be easily stretched or deformed. To know how resistant materials are to deformation, a quantity called a modulus is measured. Modulus is generally the resistance of a material or product to deformation. There are different types of modules in polymers and plastics, including tensile modulus, torsional modulus, shear modulus, and flexural modulus. In this article, we will standardize with Flexural modulus and its measurement method in High Impact Polystyrene (HIPS).

Flexural modulus

Flexural modulus Test

Flexural modulus Test

Flexural strength, also called fracture modulus, rupture modulus, and elasticity. It is a property of the material and indicates the maximum amount of compressive or tensile stress that the test material can withstand in the flexural test before failure. In other words, flexural strength indicates the highest amount of stress tolerable by the material before the breaking point.

Mathematically, the slope of the stress-strain curve is also measured in units of force on the surface (Newtons per square millimeter).

Modules of plastic materials such as High Impact polystyrene (HIPS) are very important due to the effect on mechanical properties in the correct choice of materials and also to design products for various uses. Awareness of it can save the material production process economically.

Parameters affecting the flexural modulus

The flexural modulus in a substance is strongly influenced by the binding energies of its atoms. The stronger these forces, the higher the flexural modulus of elasticity of the material. Finally, it increases the melting point of the material.

If we increase the temperature of the material, the motion of its molecules will increase, and increasing these movements will reduce the energy required to separate the molecules from each other, and as a result, the amount of flexural modulus of the material will decrease.

Standard flexural modulus measurement test

The standard flexural modulus (elasticity) test generally measures the strength of a material against deformation in the flexural state. This is usually true for materials that are rod-shaped (with a cross-section in the shape of a circle) or rectangular. In this test, almost all the details of the resistance of the sample against flexural forces are evaluated.

The flexural test is performed in two ways, three-point, and four-point, by the tensile testing device. The most common type for HIPS samples is the three-point test.

In this test, the device software plots the amount of force applied and the amount of bending of the HIPS specimen in a graph. In it, the vertical axis represents the tensile force and the horizontal axis represents the amount of flexure or the same strain.

The method of this test is performed by ISO 178 and ASTM D790. To perform the test, the sample must first be prepared by machining and cutting the product or injection molding. The length of the rectangular sample should be 20 times the thickness and its width varies depending on the thickness.

For example, if the thickness of the sample is between 1 and 3 mm, its width should be equal to 25 mm, and if the thickness of the sample is between 3 to 5 mm, the width of the sample should be equal to 10 mm.

  • Then, the sample is placed on two holders with a distance of 16 times the thickness of the sample and in the center of them as shown below.
  • The diameter of the supports should be 4 mm for samples less than 3 mm thick and 10 mm for samples with a thickness of 3 to 5 mm.
  • The diameter of the force input lever to the sample in the test is equal to 10 mm.
  • After placing the HIPS sample in the indicated location and entering the sample dimensions in the software, the jaw of the device goes down at a speed of 1 mm per minute and flexing the desired sample.

This test method is called three-point flexing because in this method, two supports are considered as two points and the third point is the point of contact of the sample with the force input lever.

After the specimen is subjected to flexural force, the amount of modulus and the amount of flexural strength are tested according to the dimensions of the specimen. Then the applied load can be calculated through the formula presented below or the stress-strain curve.

Flexural modulus formula

Flexural modulus formula

Flexural strength

E: flexural modulus

W: the force applied

d: Sample thickness

b: Sample width

L: The distance between the two locations of the sample on the device

Polymer Shaping
18 Feb
Uncategorized

What do you know about the types of polymer shaping technology?

In important industries, polymers are divided into four groups: rubber, plastics, fibers, and adhesives. Polymers are also divided into three main groups in terms of source, which are: natural polymers, modified natural polymers, and synthetic polymers. In the following, we will first get acquainted with different types of polymeric materials and then with their preparation methods and polymer shaping technology.

Resins

Resins are polymers that are easily formed but have little durability. The sources of resins are animals, plants, and minerals. Modified natural resins include cellulose and protein. Cellulose is the main component of plants that is used as an available raw material for the production of plastics. Casein made from milk is the only protein-derived plastic that has been relatively successful in business.

Synthetic polymers

Synthetic polymers can be prepared by polymerization reactions. These polymers can be used in the production of adhesives, paints, insulating containers, medical supplies, as well as in the production of fast vehicles, boats, musical instruments, home appliances, etc.

Biodegradable polymers

Biodegradability means that the polymer decomposes at high temperatures. These polymers have received a great deal of attention in basic research and the chemical and pharmaceutical industries over the last three decades. Today, biodegradable polymers are mainly used in controlled drug delivery and release systems, surgical sutures, and bone fracture repair, as well as implant capsules.

Polystyrene

Polystyrene is widely used in the manufacture of resins such as fiberglass, rubber production, intermediate materials, ion exchange resins, and in the production of copolymers such as ABS and SBR. Packaging materials, electrical and thermal insulation, pipes, and car parts are examples of polystyrene products.

Silicone rubbers

Silicone rubber is a mixture obtained by polymerization of various floods and siloxanes. Despite their high price, these materials show considerable resistance to heat. The characteristics of these compounds are low viscosity (in high percentages of resin), non-toxic, relatively low employability, high dielectric properties, and insolubility in water and alcohols.

Due to these properties, silicon compounds can be used as hydraulic fluid and heat transfer, lubricant and lubricant, alarm for electrical applications, resin coatings, and high-temperature resistant coatings and polishing materials.

Urethane rubber

These polymers are obtained by the reaction of polyglycols with organic diisocyanates. These materials are used in the manufacture of furniture, mattresses, insulation, oscillators, etc.

Familiarity with processes and polymer shaping technology

Polymer Shaping Processes

Polymer Shaping Processes

The conversion of raw polymers into final products involves a series of industrial processes. The first step involves mixing the additives with the polymer to achieve the required modifications in the properties of the raw polymer.

The second stage is the stage of shaping and creating the desired shape. An important feature in most polymer shaping processes is the preparation of polymeric materials in a softened state and proportion to the formation stage. This softening is usually achieved by heating the polymer, and finally, the shape adjustment is done by cooling or performing a chemical process to create cross-links to achieve the desired dimensions.

Polymer production processes can be generally divided into continuous processes and discontinuous processes. In the continuous process, the raw materials enter the process continuously.

In discontinuous processes such as molding processes, there is always the possibility of change and lower efficiency due to the process being performed in a short time and the presence of unproductive parts.

Among the polymer shaping technologies, the following can be mentioned:

Extrusion

Extrusion is one of the most practical methods of polymer shaping and is a continuous process to produce polymer products. In this process, the raw materials enter the extruder after passing through the feed hopper and are melted due to heat and shear stresses, and enter the conduction section. The molten material is then pressed to form the desired shape and finally cooled to stabilize the created shape.

Injection molding process

Injection molding is a discontinuous process and each cycle can create a sample. In this process, the polymer raw materials are compressed inside the mold after melting and after a period (called cooling time), they form the mold and then come out. The time and stages of this process depend on the type and physical properties of the polymeric material.

Blow molding

In this process of polymer shaping, the polymer is inserted as a hollow cylinder in a mold with a special and desired design. Then, due to pressure, the molten polymer is directed to the wall of the mold and finally forms the mold.

Film production

Film production

Film production

Plastic film is a thin sheet of plastic that is produced using the blow molding or molding process. In the blowing method, the polymer enters the extruder mold after melting and exits as a hollow cylinder under wind pressure.

Thermoforming

In this process, polymer plates are considered as the raw material. In this way, the polymer plate is softened to the temperature of the soft point, and then by applying positive or negative air pressure, the polymer is directed to the mold wall. Finally, the final material is removed from the mold after cooling.

Calendaring

The production of thin plastic sheets using the squeezing and guiding of plastic through the tight space between two or more roller bodies is called the rolling process. This method is very suitable for heat-sensitive materials such as PVC. This method is used in the paper, textile, and metal industries.

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