1. IN THE NAME OF GOD
SUBJECT:
Hydrolytic Degradation

2. Hydrolytic Degradation:
 This
process occurs in polymers that are watersensitive active groups, especially those that
take a lot of moisture.
 Polymers that have an ability for hydrolytic
destruction usually have heteroatoms in the
main or side chain.
hydrolysis :
the scission of chemical functional groups by
reaction with water. some polymers are very stable
to hydrolysis

4. Water Absorption
 Plastics
absorb water to varying
degrees, depending on their molecular
structure, fillers and additives
 Adversely affects both mechanical and
electrical properties and causes swelling
 Measures the amount of water absorbed
as a percent of total weight

5.  Exposing
plastics to moisture at
elevated temperature can lead to
hydrolysis
A
chemical process that severs polymer
chains by reacting with water
 Reduces the molecular weight and
degrades the plastic
 Degree
of degradation depends on
 Exposure
time
 Temperature
 Stress levels

6.  degradation









rate dependent on
hydrophobicity
crystallinity
Tg
impurities
initial molecular weight, polydispersity
degree of crosslinking
manufacturing procedure
geometry
site of implantation

7.  Hydrolytic
Degradation can also be
harmful and helpful in cases, for example:
Hydrolytic chain scission of the ester linkage
of polyester is the fastest and the most
“harmful” degradation process, as it causes
a considerable reduction in the molecular
weight and in the mechanical properties of
the polymer. but The polymer degradation
useful for Controlled Drug Delivery System

8. For most biodegradable
materials, especially artificial
polymers, passive hydrolysis is the most
important kind of degradation . There are
several factors that influence the velocity of
this reaction; the most important are:
 type of chemical bond
 PH
 copolymer composition
 water uptake
 morphology

9. Hydrolysis tests

The hydrolytic degradation test was
performed in a basic aqueos solution at pH
12.7 at 50 °C. Each sample was in kept in a
sealed container with 50 ml of solution. The
degradation media was changed regularly so
that the pH was maintained and polymer
matrix samples were taken after time intervals.
Degraded specimens were collected at
desired intervals and dried for 24 h in a
vacuum oven at room temperature, and then
the weight loss was measured

10. Hydrolytic Degradation Behavior of Biodegradable
Polymers from Controlled Drug Delivery System:

There are different types of polymer degradation
such as photo, thermal, mechanical and
chemical degradation. For in-vivo application;
thermal degradation is not of much significance.
biodegradable polymers contain hydrolysable
bonds making them more prone to chemical
degradation via hydrolysis or enzyme-catalyzed
hydrolysis. Enzymatic degradation does not play
significant role in polymers belonging to
lactide/glycolide family. Therefore, study of
hydrolytic degradation is utmost important while
considering performance of polymeric implants
or polymeric drug delivery system.

11. Mechanism of Polymer
Degradation and Erosion:

The difference between polymer “degradation“
and “erosion“ is not clear in many cases.
Biodegradable polymers undergo hydrolytic
bond cleavage to form water soluble
degradation products that can dissolve in an
aqueous environment, resulting in polymer
erosion . In this context, degradation is a
chemical phenomenon and erosion
encompasses physical phenomena, such as
dissolution and diffusion. Polymer degradation is
the key route of erosion.

12. 
Polymer erosion is so far more complex than
degradation, because it depends on many
other processes, such as
degradation, swelling, dissolution and
diffusion of oligomers and monomers, and
morphological changes. The erosion of a
polymer matrix can proceed through two
alternative physical mechanisms: (a) surface
erosion and (b) bulk erosion. For ideal surface
erosion, erosion rate is constant and
proportional to external surface area. For bulk
eroding polymers such as PLA and
PLGA, things are more complicated as they
have no constant erosion rate

13.  One
is homogeneous or bulk erosion, in which
hydrolysis occurs simultaneously throughout
the entire specimen.Hence, the decrease in
molecular weight, the reduction in mechanical
properties, and the loss of mass also occur
throughout the entire specimen at the same
pace. Polymers containing ester, ether, and
amide groups, such as poly(lactic acid)
(PLA), poly(glycolic acid), poly(εcaprolactone), polyamide, proteins, and
cellulose (and its derivatives), generally exhibit
this type of erosion.

14.  These
reactions can sometimes be catalyzed
by the polymers’ own hydrolysis products.
The other type is heterogeneous or surface
erosion, in which hydrolysis mainly occurs in
the region near the surface, whereas the
bulk material is only slightly or not at all
hydrolyzed. As the surface is eroded and
removed. Polymers such as poly(ortho ester)s
(POEs), PAHs, and some polycarbonates
tend to undergo surface erosion.

16. Mechanism of Hydrolytic Degradation
 Hydrolytic
degradation of members of the
polylactide/glycolide family proceeds through
four stages as represented in Figure 2: First
stage of water diffusion followed by second
stage, in which oligomers with acidic endgroups autocatalyze the hydrolysis reaction. A
critical molecular weight is reached at the
beginning of third stage,and oligomers start to
diffuse out from the polymer. Water molecules
diffuse into the void created by the removal of
the oligomers, which in turn encourages
oligomers diffusion.

17.  Marked
decrease in polymer mass and a
sharp increase in the drug release rate occur
during third stage as the drug diffuses from
the porous regions. In fourth stage, polymeric
matrix become highly porous and
degradation proceeds homogeneously and
more slowly .

19. Factors Influencing Polymer
Degradation:

In recent years a number of parameters have
been identified that influence the polymer
degradation. Among them are the
copolymer composition
, morphology, autocatalysis by acidic
degradation products inside a matrix
, presence of drugs or other excipients and
preparation technique. However, the impacts
of these parameters that increase or
decrease the degradation rate are not
exactly clear. Review on effect of various
factors on polymer degradation is presented
in Table 1.

21. Hydrolytic Degradation Behavior of Poly(butylene
succinate)s with Different Crystalline Morphologies
 The
effects of crystallinity and morphology on
polymer hydrolysis were studied for a decade.
It is known that hydrolytic degradation
proceeds at a higher rate in the amorphous
region than in the crystalline region. The higher
degradation rate in the amorphous region is
attributed to the easy diffusion of water
molecules into the interior of polymers.

23. Techniques Used to Study
Polymer Degradation:
 Hydrolytic
degradation and erosion were
then followed through time by FTIR
spectroscopy and weight loss
measurements. In the solid state, titration of
acid end group, infrared (IR) spectroscopy
and intrinsic viscosity were used to analyze
the hydrolytic degradation in order to define
the degradation rate.

25. REFERENCES:
 http://www.sbaoi.org.
 CHARACTERIZATION AND DEGRADATION
MECHANISMS OF ALIPHATIC POLYESTERS.
 Degradation as a Method of Modification of Polymeric
Products.
 From Wikipedia, the free encyclopedia
 www.sciencedirect.com