18 Questions
The x-ray diffraction pattern of a semicrystalline polymer is comprised of two main features: a distinct diffraction peaks corresponding to the ______ phase and a broad 'halo', corresponding to the ______ phase.
crystalline, amorphous
If any ______ material crystallized, there would be a resulting exothermic peak as heat is given off during crystallization.
amorphous
Most Polymers have ______ and Crystalline Regions.
Amorphous
Polymers are rarely 100% ______.
crystalline
For crystalline polymers, the overall ______ may range from as low as 30% to as high as 90%; and the remaining fraction of the polymer chain are ______.
crystallinity, amorphous
The area under the crystallization peak is ______ and the crystalline fraction can be determined by measuring the net heat flow associated with the crystalline melting event.
enthalpy
Most individual polymer chains will traverse both the ______ and amorphous regions.
crystalline
All semicrystalline polymers can be viewed as two-phase materials, with inter-connected ______ and amorphous phases.
crystalline
Note that all semicrystalline polymers can be viewed as two-phase materials, with inter-connected crystalline and ______ phases.
amorphous
The crystal forms at a nucleus, and grows outward as a ______ as new chain segments add to the crystal.
spherulite
Dislocations involve a mismatch or distortion in the arrangement of polymer chains, leading to localized ______ fields.
strain
Dislocations that occur along the edge of a polymer crystal or grain boundary are known as ______ dislocations.
edge
Polymers can have both ______ (disordered) and crystalline (ordered) regions within their structure.
amorphous
[Blank] regions lack long-range order.
amorphous
The ratio of crystalline to ______ regions affects the polymer's mechanical properties, such as stiffness and strength.
amorphous
Polyethylene is a thermoplastic polymer consisting primarily of long chains of ______ monomer units.
ethylene
Low-Density Polyethylene has a more ______ structure, which gives it lower density and flexibility.
branched
High-Density Polyethylene has a more ______ structure, leading to higher density and greater strength and stiffness.
linear
Study Notes
Crystalline Regions in Polymers
- Polymers can have both amorphous (disordered) and crystalline (ordered) regions within their structure
- Crystalline regions occur when polymer chains arrange in an ordered manner, while amorphous regions lack long-range order
- The ratio of crystalline to amorphous regions affects the polymer's mechanical properties, such as stiffness and strength
Hydrocarbons in Polymers
- Hydrocarbons serve as the building blocks or monomers for synthesizing various types of polymers
- Examples of polymers include:
- Polyethylene (PE)
- Low-Density Polyethylene (LDPE): more branched structure, lower density, and flexibility
- High-Density Polyethylene (HDPE): more linear structure, higher density, and greater strength and stiffness
- Polypropylene (PP)
- Known for its strength, resistance to fatigue, and versatility
- Polyethylene (PE)
Crystalline Morphology
- Polymers crystallize by nucleation and growth, forming spherulites as new chain segments add to the crystal
- Crystallization rate is a strong function of temperature, reflecting a trade-off between two factors
- Spherulites eventually impinge, and crystallization stops
Line Defects in Polymers
- Line defects, or dislocations, are one-dimensional defects that occur along specific lines or planes within the polymer structure
- Dislocations involve a mismatch or distortion in the arrangement of polymer chains, leading to localized strain fields
- Types of line defects include:
- Edge Dislocations: occur along the edge of a polymer crystal or grain boundary
Thermal Transitions in Polymers
- Thermal transitions can be observed by Differential Scanning Calorimetry (DSC)
- Exothermic peak occurs during crystallization, releasing heat
- The area under the crystallization peak is enthalpy
- Crystalline fraction can be determined by measuring the net heat flow associated with the crystalline melting event
Properties of Crystalline Polymers
- General properties include:
- Great amount of shrinkage during cooling of the molded part
- More strength and stiffness
- Increased brittleness
Crystalline Regions in Semicrystalline Polymers
- Crystalline regions are created when the chain folds onto itself, forming thin platelets with chain folds at faces
- Most polymers have crystalline and amorphous regions
- Polymers are rarely 100% crystalline
- Heat treating causes crystalline regions to grow and %crystallinity to increase
This quiz covers the characteristics of semicrystalline polymers, including their x-ray diffraction patterns and thermal transitions observed through DSC. Test your knowledge of crystalline and amorphous phases in polymers.
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