Two types of plastics/polymers:
Thermoplastics Polymers
Thermoplastics are resins that repeatedly soften when heated and harden when cooled.
OR
Thermoplastics Polymers are resins that repeatedly soften when heated and harden when cooled.Crystallineity in Polymers: A small region of a macromolecules materials in which portions of large molecules are arranged in regular way, is called crystalline. Crystallization imparts a denser packing of molecules, thereby increasing the intermolecular forces of attraction. This accounts for a higher and sharper softening point, greater rigidity and strength and greater density. A completely crystalline polymer tends to acquire brittleness.
OR
They are usually formed by addition of polymerization and condenzation. They consist of two dimensional long chain loner polymers with negligibly coss-link. They are softening on heating readily, because secondary force B/w the individual chain can break easily by heat or pressure or both. Aluminum and steel mould are used. It is due to the fact that, they are smoother (low porosity), they provide more uniform surface finish than cast aluminum. Aluminum moulds require steel or hardened pinch off inserts to prevent coining of parting line. The engineering thermoplastics offer a number of performance advantages compared with polyolefin materials. Greater stiffness or the ability of a material to resist deflection under load. Higher resistance to stretching.
Polyethylene (PE)– used in making garbage bags;
Polyvinyl chloride (PVC)– used for house siding;
Polypropylene (PP)– used as carpet fibers, packaging, and diapers.
Thermosetting Polymers
Thermosets are resins that undergo chemical changes during processing to become permanently insoluble and infusible due to they formed three-dimensional cross linked network structure when heat is applied.
OR
Thermosets are resins that undergo reaction during processing to become permanently insoluble and infusible due to they formed three-dimensional cross linked network structure when heat is applied.
Molecular weight “of a polymer is defined as sum of the atomic weight of each of the atoms in the molecules, which is present in the polymer”.
OR
They are usually formed by condenzation polymeration, they have three dimensional network structures, they cross-link and fond retain. They strength on heating and hence, they do not soften on heating. They retain their shape and structure even on heating, hence the can’t be reshaped a reused. They cannot be rechanched form waste. Thermoset plastic can’t be recycled be cause. It consists of so many cross-links and it has three dimensional structures. The cross-link and bond retain their strength or heating and hence. They do not soften on heating. That we cannot recycle thermoset plastic.
Epoxy– used for adhesives and coatings;
Polyurethanes (PURs)– used in foams and coatings.
In addition to these basic characteristics, polymers provide the frp composite designer with a myriad of characteristics that can be selected, depending on the application. Combined with reinforcement of the polymer matrix, a vast range of characteristics are available for frp composites.
The properties of frp composites are measured the same way that traditional materials are measured so that comparisons can be made for evaluation.
Characteristics of thermosetting resins:
During the hardening the cross-links are formed between adjacent molecules, resulting in a complex, interconnected network that can be related to its viscosity and performance
These cross-links prevent slippage of individual chains, thus preventing plastic flow under addition of heat
If excessive heat is added after cross links, degradation rather than melting will occur.
In general, frp composites utilize a thermoset plastic.
A plastic in which the polymer molecules are not crosslinked (not chemically bonded to other polymer molecules) is a thermoplastic. Since the molecules are not connected by crosslinks, it allows the molecules to spread farther apart when the plastic is heated. This is the basic characteristic of a thermoplastic; the plastic will soften, melt, or flow when heat is applied. Melting the plastic and allowing it to cool within a mold will form the finished product.
Difference Between Thermoplastics and Thermosetting Polymers
Typical measurements include:
Compressive Strength -Describes how much of a load a material can take before it is crushed or fractured
Flexural Modulus -A number associated with the flexibility or stiffness of a material. It indicates how far a material will bend when a certain load is applied to it. The lower the modulus, the more flexible the material.
Flexural Strength– Measures how much of a load a material can take before it fractures or breaks when it is in the process of being bent.
Impact Strength –There are two primary impact tests; one is calledIZOD impact and the other is called Gardner impact. IZOD impact measures the energy required to fracture or break a material when it is struck on its edge. Gardner impact measures the energy required to damage or puncture a material when it is struck on its front surface.
Rockwell or Barcol Hardness -Measures the surface hardness of a material. The higher the hardness value, the more resistant a material is to scratching, abrasion, and denting.
Tensile Modulus -A number associated with pulling or stretching a material (tension) and how much it elongates when a certain load is applied to it. The lower the modulus, the more the material will elongate or stretch.
Tensile Strength– Measures how much of a load a material can take before it fractures or breaks when it is in the process of being stretched.
THERMO PLASTIC:
इसे कई बार प्रयोग किया जा सकता है
ये गरम करने पर गरम होता हैऔर ठंडा करने पर कठोर होता है
उत्पादन के बाद इसमें भौतिक परिवर्तन होता है
इस प्लास्टिक से वास्तु बनाते समय हर विधि का प्रयोग किया जा सकता है
Material Name Short Name Shrinkage Melting Point
PE: POLYETHYLENE पोलीएथीलीन
Low density polyethylene LDPE 0.91-0.92 110
High density polyethylene HDPE 0.94-0.96 130
Linear low density polyethylene LLDPE 0.91-0.93 125
High molecule HDPE HMHDPE 0.94-0.97 135
Ultra high molecular HDPE UHMHDPE 0.97 130
Polypropylene PP 0.89-0.91 160
USES:
EXRTUSION BLOW, PIPE, COATING, FILM MOULDING
INJECTION MOULDING
BLOW MOULDING
ROATIONAL MOULDING
THERMOFORMING
Chlorinated polymers:
Polyvinyle chloride PVC 1.38-1.41 160-220
Polyvinyle dene chloride PVDC 1.65-1.75 190-200
Chlorinate PVC PVCC 1.44-1.47 200-210
Co-polymer of vinyle
chloride & vinyle acetate PVCCOVA 1.16-1.36 130
Fluorinated polymer:
Polyvinyle fluoride PVF 1.44 200
Polyvinyle dene fluoride PVDF 1.76-1.77 172
Poly chloride tri fluoro ethylene PCTFE 2.10-2.30 210
Poly tetra fluoro ethylene PTFE 2.10-2.30 320
Poly styrene & co polymers:
Acryl nitrite butadiene styrene ABS 1.07-1.10 200-210
Styrene acryl nitrite SAN 1.06 200
Polystyrene PS 1.04-1.07 190
Polyamides:
Nylon 6 PA6 1.10-1.16 215
Nylon 66 PA66 1.09-1.14 265
Nylon 11 PA11 1.04-1.10 190
Nylon 12 PA12 1.01-1.02 180
Nylon 6,10 PA6,10 1.07-1.09 210
Acrylic Polymer:
Poly Mehta methyl aculeate PMMA 1.17-1.20 190
Poly acryl nitrite PAN 1.16-1.19
Acetyl polymers:
Poly oxeye ethylene (homo) POM 1.43 175
Poyoxy methylene (com) POM 1.41 163
Esters:
Polycarbonate PC 1.2 220
Polyethylene terephthalate PET 1.37 225
Polybutylene terephthalate PBT 1.32 225
Polyurethanes:
Polyurethane (linear) PVR 1.17-1.22 150-185
Cellulosic polymers:
Cellulose acetate CA 1.25-1.35 230
Cellulose acetate butyrate CAB 1.15-1.25 180
Cellulose nitrate CN 1.58-1.66 180
Cellulose propionate CP 1.20-1.24 180
THERMOSET MATERIAL:
इसे कई बार प्रयोग नहीं किया जा सकता
ये गरम करने पर सेट हो जाता है और सेट होने के बाद दोबारा प्रयोग में नहीं लाया जा सकता
उत्पादन के बाद इसमें भौतिक एवं रासयनिक परिवर्तन नहीं होते
इस प्लास्टिक से वास्तु बनाते समय केवल Compression Moulding एवं Injection Transfer Moulding में प्रयोग किया जा सकता है
MATERIAL PRESSURE TEMPERATURE
PF: PHENOL FORMAL DEHYDE 105-280 290-350
MF: MELAMINE FORMAL DEHYDE 140-560 280-350
UF: UREA FORMAL DEHYDE 140-560 275-310
POLYESTER
EPOXY RESIN 150-580 290-390
POLYSTE RESIN
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