Bangladesh University of Textiles
An Assignment on Acrylic
Course Title: Polymer Science & Engineering
Course Code: WPE 101
Submitted By, Submitted To,
Farhana Hossain Suraiya Md. Rashedul Islam
ID: 23010701005 Assistant Professor
Department: IPE Department of Wet Process
Engineering
Definition
Acrylics are a family of synthetic polymers derived from acrylic acid
(CH₂=CHCOOH), methacrylic acid (CH₂=C(CH₃)COOH), or their derivatives, such as
esters and amides. The term acrylic is often used interchangeably with poly
methyl methacrylate (PMMA) which is the most commercially significant member
of this family. PMMA is a transparent thermoplastic known for its clarity, rigidity,
and weather resistance. However the term acrylic also encompasses other
polymers including polyacrylonitrile (PAN) which is used to produce acrylic fibers
for textiles.[1,4]
Types
The versatility of acrylics stems from the ability to modify their properties through
combining two or more different monomers. This leads to various types:
PMMA (Poly methyl methacrylate): This homopolymer is the most
common acrylic. It's known for its excellent optical clarity, good resistance
to UV degradation and environmental factors and relatively high rigidity.[6]
Modified Acrylics: These are copolymers where methyl methacrylate is
combined with other monomers such as acrylates or other methacrylates.
These modifications can enhance specific properties:
o Impact Resistance: Adding butyl acrylate can significantly improve
the impact strength of PMMA which makes it less brittle.
o Flexibility: Copolymers with higher proportions of acrylates tend to
be more flexible and less rigid.[5]
Acrylic Fibers (PAN-based): These are produced from polyacrylonitrile
(PAN). Pure PAN is difficult to process, so it is usually copolymerized with
small amounts of other monomers to improve dyeability and processability.
Acrylic fibers are used in textiles, carpets and other applications where
warmth and resilience are desired.[4]
Manufacturing/Composition (Focus on PMMA)
PMMA is synthesized through the free-radical polymerization of methyl
methacrylate (MMA) monomers. This process involves three main steps:
initiation, propagation, and termination.
Initiation:
o This step involves the generation of free radicals which are highly
reactive species with unpaired electrons. This is typically achieved by
using an initiator such as an organic peroxide or an azo compound.
o The initiator decomposes upon heating or exposure to UV light to
generate free radicals.
o Reaction using benzoyl peroxide:
(C₆H₅COO)₂ → 2 C₆H₅COO•
C₆H₅COO• → C₆H₅• + CO₂
o These free radicals then attack the double bond of the MMA
monomer, initiating the polymerization chain.
o Reaction:
R• + CH₂=C(CH₃)(COOCH₃) → R-CH₂-C•(CH₃)(COOCH₃) [1]
Propagation:
o In this step the free radical attached to the MMA monomer reacts
with another MMA monomer adding it to the growing polymer chain.
This process repeats rapidly adding more and more monomers to the
chain.
o Reaction:
R-CH₂-C•(CH₃)(COOCH₃) + CH₂=C(CH₃)(COOCH₃) → R-CH₂-C(CH₃)
(COOCH₃)-CH₂-C•(CH₃)(COOCH₃) [1]
Termination:
o The polymerization process ends when two free radicals
combine neutralizing each other and stopping the chain
growth. This can occur through:
Combination: Two growing polymer chains combine directly.
Reaction:
2 R-(CH₂-C(CH₃)(COOCH₃))n• → R-(CH₂-C(CH₃)(COOCH₃))₂n-R
Disproportionation: A hydrogen atom is transferred from one
growing chain to another, resulting in one polymer chain with
a saturated end and another with an unsaturated end.
Reaction:
2 R-(CH₂-C(CH₃)(COOCH₃))n• → R-(CH₂-C(CH₃)(COOCH₃))nH +
R-(CH₂-C(CH₃)(COOCH₃))n [1]
As mentioned before, these reactions can be carried out using different
polymerization techniques:
Bulk Polymerization: MMA is polymerized directly without any solvent.
This method is relatively simple but can be challenging to control due to the
high viscosity of the polymerizing mixture and the exothermic nature of the
reaction (heat is released). This heat can cause uncontrolled polymerization
or even degradation of the polymer. [5,6]
Solution Polymerization: MMA is dissolved in a solvent before
polymerization. This helps control the reaction temperature and viscosity
but requires a subsequent step to remove the solvent.[5]
Suspension Polymerization: MMA is dispersed as droplets in water, and
polymerization occurs within these droplets. This results in small beads or
pearls of PMMA. [3]
Emulsion Polymerization: MMA is emulsified in water using surfactants,
and polymerization occurs within micelles (aggregates of surfactant
molecules). This method produces a latex or dispersion of PMMA particles.
[3]
The chemical structure of PMMA consists of long chains of repeating methyl
methacrylate units: [CH₂C(CH₃)(COOCH₃)]n. The presence of the methyl group
(CH₃) and the ester group (COOCH₃) influences the properties of PMMA, such as
its glass transition temperature and its resistance to certain solvents.
Properties (PMMA)
Strength: PMMA has good tensile strength and flexural strength. However,
it is relatively brittle, meaning it can fracture easily under impact or sharp
blows.[3]
Glass Transition Temperature (Tg): The Tg of PMMA is approximately
105°C. This is the temperature above which the polymer transitions from a
hard, glassy state to a more rubbery or flexible state.[3]
Melting Temperature (Tm): PMMA is an amorphous polymer, meaning it
lacks a distinct crystalline structure. Therefore, it does not have a sharp
melting point like crystalline materials. Instead, it softens gradually over a
range of temperatures above its Tg.[3,7]
Boiling Point: PMMA will degrade chemically before reaching a boiling
point in the traditional sense. Heating it to high temperatures will cause
depolymerization and the release of volatile products.[3]
Chemical Resistance: PMMA exhibits good resistance to many chemicals,
including dilute acids, alkalis, and aliphatic hydrocarbons. However, it is
susceptible to attack by strong solvents like ketones, esters and chlorinated
hydrocarbons.[3,1]
Optical Properties: PMMA is highly transparent, with excellent light
transmission (around 92%) and low haze (minimal scattering of light). This
makes it suitable for optical applications.[7]
Weatherability: PMMA has excellent resistance to weathering, including
UV radiation, moisture, and temperature changes. This makes it suitable for
outdoor applications. [7]
Uses
The combination of properties described above makes PMMA suitable for a wide
range of applications:
Glazing and Signage: Its clarity and weather resistance make it ideal for
windows, skylights, signs, displays and lighting fixtures.
Automotive: Used in tail lights, instrument panels, lenses and other interior
and exterior components.
Medical: Used in prosthetics, dental materials and medical devices where
biocompatibility and sterilizability are important.
Electronics: Used in light guides for LCD screens, optical fibers and other
electronic components.
Consumer Goods: Used in furniture, kitchenware, bathroom fixtures and
other household items.[3,6,7]
References
1.
Brandrup, J. I. (1999). Polymer handbook. John Wiley & Sons.
2.Brydson, J. A. (1999). Plastics materials. Butterworth-Heinemann.
3.Callister Jr, W. D. (2018). Materials science and engineering an introduction. John Wiley & Sons.
4.Crawford, R. J. (2012). Plastics engineering. Butterworth-Heinemann.
5.Odian, G. (2004). Principles of polymerization. John Wiley & Sons.
6.Sperling, L. H. (2006). Introduction to physical polymer science. John Wiley & Sons.
7.Strong, A. B. (2006). Plastics: materials and processing. Pearson Education.
