Group members Rahamat Ullah, MD. Ashraful Amin, and Neamul Haque from Daffodil International University presented on crystallinity in polymers. They discussed that crystallinity refers to the structural order of atoms or molecules in a solid. There are two types of polymers: crystalline polymers, which are rigid and high melting, and amorphous polymers. The regular structure of polymer molecules allows them to form lamellar crystals. A polymer's crystallinity depends on its structure - orderly polymers easily form crystals while irregular polymers are amorphous. The degree of crystallinity influences various material properties such as mechanical strength, opacity, and thermal behavior.

1. Presented By Group 10 members of
1) MD. ASHRAFUL AMIN ID : 111-23-2399
2) RAHAMAT ULLAH ID: 111-23-2411
3) NEAMUL HAQUE ID: 111-23-2406
PRESENTATION ON
CRYSTALLINITY IN POLYMERS

2.  Crystallinity refers to the degree of structural
order in a solid. In a crystal , the atoms or
molecules are arranged in a regular, periodic
manner . In a gas, the relative positions of the
atoms or molecules are completely random.
Amorphous materials, such as liquids and
glasses, represent an intermediate case . There
are two types of polymers 1) Crystalline polymers
and 2) Amorphous polymers

3.  Crystalline Polymers
 Highly crystalline polymers are rigid, high
melting, and less affected by solvent
penetration. Crystallinity makes a polymers
strong, but also lowers their impact
resistance. As an example, samples of polyethylene
prepared under high pressure (5000 atm) have high
crystallinities (95 - 99%) but are extremely brittle .

4.  Small molecules and ions form a three-
dimensional lattice with an extended regular
structure that makes large crystals possible. A
small portion of the NaCl lattice is modeled in the
diSmall molecules and ions form a three-
dimensional lattice with an extended regular
structure that makes large crystals possibleagram
at the right.

5.  We usually describe such lattices with a unit cell -
the smallest repeating unit in the lattice . In the
case of NaCl, the unit cell is said to be face-
centered cubic.
Polymer molecules are very large so it might seem
that they could not pack together regularly and form
a crystal. It now is known that regular polymers may
form lamellar (plate-like) crystals with a thickness of
10 to 20 nm in which the parallel chains (shown in
different colors in the simulated structure below
) are perpendicular to the face of the crystals.

6.  Crystallinity and polymer structure
 A polymer's structure affects crystallinity a
good deal. If it's regular and orderly, it will
pack into crystals easily. If it's not, it won't.
It helps to look at polystyrene to understand
how this works.
As we can see on the lists above, there are two kinds of polystyrene.
There is atactic polystyrene, and there is syndiotactic polystyrene. One is
very crystalline, and one is very amorphous.

8.  Syndiotactic polystyrene is very orderly, with the phenyl groups
falling on alternating sides of the chain. This means it can pack
very easily into crystals.
 But atactic styrene has no such order. The phenyl groups come
on any which side of the chain they please. With no order, the
chains can't pack very well. So atactic polystyrene is very
amorphous.
 Other atactic polymers like poly(methyl methacrylate) and
poly(vinyl chloride) are also amorphous. And as you might expect,
stereoregular polymers like isotactic polypropylene and
polytetrafluoroethylene are highly crystalline.
 Polyethylene is another good example. It can be crystalline or
amorphous. Linear polyethylene is nearly 100% crystalline. But
the branched stuff just can't pack the way the linear stuff can, so
it's highly amorphous.

10.  The crystallinity of a material influences
many of its characteristics, including
mechanical strength, opacity, and
thermal properties. The degree of
crystallinity has a big influence on
hardness, density, transparency and
diffusion.

11.  THANKS A LOT TO LISTING OUR
PRESENTATON WITH PATIENT
ON BEHALF OF DAFFODIL INTERNATIONAL
UNIVERSITY
BY RAHAMAT ULLAH
rahamat.tex@gmail.com and
www.facebook.com/r.u.joy