1. Simultaneous improvements in the
Cryogenic Tensile Strength, Ductility and Impact
Strength of Epoxy resins by a Hyperbranched polymer
by Jiao-Ping Yang, Zhen-Kun Chen, Guo Yang, Shao-Yun Fu, Lin Ye
Ramesh Ramachandran
Geevarghese George

2. Structures of Components

3. Pure Epoxy Resin Vs Modified Epoxy

4. Experimental

5. 2a. Experimental
● 2a.1 Materials
– Epoxy Resin: bisphenol A
diglycidyl ether (DGEBA)
– Curing Agent:
methyltetrahydrophthalic
anhydride (MeTHPA)
– Accelerator:
benzyl dimethylamine (BDMA)
– Hyperbranched Polymer:
polyester Boltorn H30
● 32 hydroxyl groups
● Amorphous solid at RT
● 2a.2 Sample Preparation
– solution of H30 in acetone + epoxy is heated to
60 deg, and a homogenous mix is formed
– Acetone evaporates during heating
– H30 content varied from 0% to 15 %
– stoichiometric amount of curing agent was
added to the mix
– Homogenous solution was casted into mold at
80 deg, then cured at 130 deg for 3 h, 150 for
10h, and post cured at 170C for 5 h

6. 2b. Testing
● Tensile Testing
– ASTM D638
– Loading Speed:
2 mm/min
– Load: 10 kN
– Cryogenic Temperature:
● Dipped samples and
clamps in LN

7. ● Impact Testing
– ASTM D256
– Specimens dipped in a liquid nitrogen for 10 mins
– Cryogenic thermocouples embedded inside →
That's how we know its 77K
● PALS (Positron annihilation lifetime
spectroscopy)
– Used to study the voids and defects on solids
– Non-destructive spectroscopy
– The positronium lifetime τ3
and intensity I3
of the
long-lived components were analyzed

8. ● DSC
– Different rates of heating 5, 10, 15 and 20 deg C/min
– Tg was also studied
● 30 to 200 deg celcius
● Heating rate 10 degC/min
● SEM
– To study fracture surfaces
– Fracture surfaces were fracture surfaces were cleaned with
alcohol and spray coated with a thin layer of evaporated
gold to improve conductivity.

9. 3. Resuts and Discussion
● Tensile Properties
● Impact Strength and SEM
● Thermal Properties

10. 3.1 Tensile Properties

12. Reminder.. One unit of the epoxy network

13. Things to note (in modified epoxy)
● Free Volume
● Free Space
● More Hydrogen Bonds
● Formed bcos of large no of unreacted Hydroxyl (-OH) groups
Bcos MeTHPA was added
stoichiometrically to cure
epoxy resin

14. ● PALS Results confirm the presence of free volume
● Positronium lifetime τ3
= shows average size of free volumes
● Intensity I3
= shows the concentration of free volumes

15. ● DSC Scan
Displays peak exotherm at the same temperatures
H30 has little effect on the cure kinetics

17. ● Increase in TS @RT:
– Due to large no of HB
– Flexible H30 reduces internal residual stresses
● Decrease in TS @RT:
– Flexible H30 decrease rigidity of polymer chain
– More free spaces and free volumes → reduces XL density
● At less than 10% H30, the latter factors are
overshadowed by the former.
● So, a net increase is seen
● Beyond this conc., the factors that decrease the TS are
predominant.
– Too much free volume and free spaces
– Too much flexibilty
epoxy resins cured at high
temperature, followed by bulk
shrinkage during cooling

18. ● TS in Cryogenated sample (77K):
– Thermal shrinkage causes
● Stronger HB than in RT case
● Reduction in free volume and free space
● Residual stresses made more severe in bulk epoxy
– But H30 helps reduce the effect of residual stresses
– Too much H30 can reduce the TS like in the RT samples
● Table 1: Modulus is decreased
● Because of incorporation of H30 (read soft, flexible)
● But compared to RT samples, it is high
– Because Thermal shrinkage
● More HB

19. ● Table 1: Faliure strain
– Lower in cryogenic samples
● Macromolecules are frozen up
● Free volumes and free spaces are reduced at 77K
– Reduction in ductility
– Ductility is increased as H30 increases
● Bcos easier mobility for macromol. as H30 (flexible, soft)
is added
– H30 added → free volume and free space increase → mobility

20. 3.2 Impact Strength

21. 3.2 SEM Analysis (RT Vs 77K)

22. 3.3 Thermal Properties
● High Tg → Restriction of Mobility:
● Large no of HB
● Hyperbranched structure of H30 (like in PS) // Steric Effect
● But H30 can also make the mobility easier! (soft, flexible)
● Decrease in XL density (PALS Result – corresponds to inc
in free volume and space) should also reduce Tg
● ALL these “decreasing – Tg – effects” is observed only
above 15% conc of H30

23. Conclusion
● Addition of H30 → improvements in the tensile
strength, failure strain and impact strength at 77 K
– Maximum tensile strength at 77 K is obtained for the
modified system with 10 wt% H30
– The elongation at break at 77 K is consistently increased by
the addition of H30
– The maximum cryogenic impact strength is obtained at 10
wt% H30.
● The observed ‘‘protonema’’ by SEM on fractured
surfaces is used to explain the RT and cryogenic
impact strength for the H30-modified epoxy resins.
● Appropriate amount of H30 does not affect Tg.
● Cryogenic engineering applications!!

24. Thank You.