MapaMetal_Plasticos
Fernando Arturo Rodríguez Lee
Created on November 21, 2024
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Transcript
Linear Visco-Elasticity
Introduction
Injection
Extrusion
Chemical Characteristics
Molecular Structure
Plastics and composites
Rheology and mechanical properties
Manufacturing processes
chemical and physical aspects
Plastics and Composites Engineering - M5036
Blown Film
Cast Film
Fiberspinning
Definition: it is a manufacturing system in which raw polymer materials are melted, shaped, and formed into continous profiles or products.
Extrusion
Size of the die
Die opening width
Film winding speed
Bubble diameter vs. die diameter
Die diameter
Die gap
Take-up speed
Blow-up ratio
Defects
Blow Molding
Definition: it is a manufacturing process where the polymer is metled, injected into a mold cavity, cooled, and solidified to form complex, precise shapes.
Injection
Back
Copolymer
Materials formed by a combination of differents monomers
Free Radical (chain growth | Condensation (byproduct release) | Catalyst (controlled growth) | Ionic (charged initiation)
Semi-crystalline | Amorphus
Thermoplastics | Thermosets
Elastomer | Fiber | Plastics
Classification
Copolymers
Chemical Origin
Crystallinity
Thermal Behavior
Use
Polymer
Mer
Definition: Long molecules composed of repeated units called mers.
Molecular Structure - Intimate nature of polymers
Back
Tg | Tm
Molecular Weight Distribution
Polymerization is the chemical processes in which monomers form large repeating molecules known as polymers. The size of this polymer created directly influence the final product behavior. Analyzing the Molecular Weight Distribution of a sample can give you insights on the chemical and mechanical characteristics of a polymer.
Molecular Weight
Polymer
Atactic
Syndiotactic
Isotactic
Spatial Orientation
Chemical Characteristics - Intimate nature of polymers
Back
Narrow Polydispersity (PDI<1): Uniform chain lenght. Results in more consistent physical and mechanical properties.
Broad Polydispersity (PDI>1): Mix of long and short chains. May enhance toughness and processing flexibility but reduce uniformity.
Polydispersity measures the breadth of a polymer's MWD.
Mn
Mw
PDI
PDI
MWD
Weight Fraction
Molecular weight
Molecular Weight Distribution of a given polymer describes how molecular weights are distributed within a sample. This distribution significantly influences the polymer's properties, including its mechanical behavior, processing characteristics, and application performance. Each molecular weight (Mn, Mw, Mz) provides specific insights into how the MWD affects a polymer's mechanical properties.
Weight Fraction
Molecular weight
Mz
Mw
Mn
Molecular Weight Distribution (MWD)
Back
Melt strength, elastic recovery, stress relaxation; governs behavior in extreme mechanical stress scenarios.
Ductility, brittleness, initial chain entanglement; affects toughness and elongation.
Tensile strength, impact resistance, elasticity; improves load-bearing capacity and energy absorption.
Mechanical Properties Affected
Mechanical Properties Affected
NiMi
NiMi
Mechanical Properties Affected
Mw
Mi is the molecular weight of a chain and Ni is the number of chains of that molecular weight
Ni
Mz takes into account the higher molecules weights, that is the ones at right tail of the MWD curve.
NiMi
NiMi
NiMi
Mn
Mz emphasizes the contribution of the longest chains in the polymer sample
Mw takes into account the molecular weight of each chain in determining contributions to the molecular weight average.
Mn
Mn is the arithmetic mean molecular weight of all polymer chains in a sample. It gives equal weight to each chain, regardless of its size
Mz
Mw
Mn
Back
- Tg: The temperature range where a polymer transitions from a rigid, glassy state to a rubbery, flexible state.
- Tm: Indicates the upper thermal limit for processing and application of the polymer
Tg and Tm
- A small sample of the polymer is placed in a pan alongside a reference pan.
- Both pans are subjected to the same temperature program (heating, cooling, or isothermal).
- The DSC measures the difference in heat flow between the sample and the reference as the temperature changes.
How does it works?
What is it?
Differential Scanning Calorimetry (DSC) is a thermal analysis technique used to measure the heat flow into or out of a polymer sample as it is heated, cooled, or held at a constant temperature. It provides valuable information about the thermal properties and transitions of polymers, which are critical for understanding their structure, processing, and performance.
DSC
Back
Models
Flow Curve Viscosity Curve
Rheology looks for a quantitative relation between the force applied and the resulting deformation or flow (or between the deformation or flow applied and the induced force)
Introduction to Rheology
Back
Viscoelasticity
- For non-Newtonian materials, the dashpot alone is insufficient to capture behavior because the viscosity changes with shear rate.
- Shear-thinning (pseudoplastic): Viscosity decreases with increasing shear rate.
- Shear-thickening (dilatant): Viscosity increases with increasing shear rate.
- In a purely Newtonian fluid, the dashpot is sufficient to describe the behavior. The viscosity ( 𝜂 η) is constant, meaning the stress is linearly proportional to the strain rate.
- This corresponds to the linear, steady shear viscosity observed in low to moderate shear rate regions for Newtonian fluids.
Non-newtonian Region
Newtonian Region
Back
Elasticity Law
Viscosity Law
Ideal-elastic solidsStone | Steel
Viscoelastic solidsPaste | gels
Viscoelastic liquidsGlues | shampoos
Ideal-viscous liquidsWater | Oils
Elastic
Viscoelastic
Viscous
Back
Constant Strain
Constant Stress
Shear Viscosity
In reality, most materials are neither purely elastic nor purely viscous; they exhibit viscoelastic behavior, meaning they have properties of both solids and liquids.
Viscoelasticity is a material's property that explains and combines the viscous and elastic behavior.
Viscoelasticity
Back
Shear rate
Shear Stress
Viscous modulus
Viscosity is a measure of fluid's resistance to flow. Shear Viscosity is the fluid's resistance to deformation under a shear force (a force applied parallel to the surface of the fluid).
Shear Viscosity
G' G''
Back
Creep and Recovery vs. Moduli: Creep and recovery tests provide time-domain insights into viscoelastic behavior, while the storage modulus (𝐺′) and loss modulus (𝐺′') represent frequency-domain properties. During creep, 𝐺′ and 𝐺'′ influence deformation, with 𝐺′ governing recovery and 𝐺′′ dictating the permanent viscous strain.
Creep: describes the time-dependent deformation of a material under a constant stress. Recovery: is the time-dependent strain reduction observed after the stress is removed.
Creep and Recovery compliance
Back
- Complex Modulus (G*):
- Represents the total resistance to deformation
- Magnitud of the overall material stiffness.
- Shear Modulus (G):
- Describes the elastic response to small deformations
- Tan delta:
- Ratio of G'' to G', describing the balance of viscous and elastic behavior.
G* G
- Storage Modulus (G'):
- Represents the elastic (solid-like behavior of a material)
- Indicates how much energy is stored and recoverded per cycle of deformation
- Loss Modulus (G''):
- Represents the viscous (liquid-like) behavior of a material.
- Indicates how much energy is lost as heat per cycle of deformation.