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

Structures of Components

Pure Epoxy Resin Vs Modified Epoxy

Experimental

2a. Experimental

2a.1 MaterialsEpoxy Resin: bisphenol A diglycidyl ether (DGEBA)

Curing Agent: methyltetrahydrophthalic anhydride (MeTHPA)

Accelerator:
benzyl dimethylamine (BDMA)

Hyperbranched Polymer:
polyester Boltorn H3032 hydroxyl groups

Amorphous solid at RT

2a.2 Sample Preparationsolution 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

2b. Testing

Tensile TestingASTM D638

Loading Speed:
2 mm/min

Load: 10 kN

Cryogenic Temperature:Dipped samples and clamps in LN

Impact TestingASTM 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 3 and intensity I3 of the long-lived components were analyzed

DSCDifferent rates of heating 5, 10, 15 and 20 deg C/min

Tg was also studied30 to 200 deg celcius

Heating rate 10 degC/min

SEMTo 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.

3. Resuts and Discussion

Tensile Properties

Impact Strength and SEM

Thermal Properties

3.1 Tensile Properties

Reminder.. One unit of the epoxy network

Things to note (in modified epoxy)Free Volume

Free Space

More Hydrogen BondsFormed bcos of large no of unreacted Hydroxyl (-OH) groups

Bcos MeTHPA was added stoichiometrically to cure epoxy resin

PALS Results confirm the presence of free volume

Positronium lifetime 3 = shows average size of free volumes

Intensity I3 = shows the concentration of free volumes

DSC Scan

Displays peak exotherm at the same temperatures

H30 has little effect on the cure kinetics

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

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 epoxyBut H30 helps reduce the effect of residual stresses

Too much H30 can reduce the TS like in the RT samples

Table 1: Modulus is decreasedBecause of incorporation of H30 (read soft, flexible)

But compared to RT samples, it is highBecause Thermal shrinkageMore HB

Table 1: Faliure strainLower in cryogenic samplesMacromolecules are frozen up

Free volumes and free spaces are reduced at 77KReduction in ductility

Ductility is increased as H30 increasesBcos easier mobility for macromol. as H30 (flexible, soft) is added H30 added free volume and free space increase mobility

3.2 Impact Strength

3.2 SEM Analysis (RT Vs 77K)

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

Conclusion

Addition of H30 improvements in the tensile strength, failure strain and impact strength at 77 KMaximum 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!!

Thank You.

Click to edit the title text formatClick to edit Master title style

Click to edit the outline text formatSecond Outline LevelThird Outline LevelFourth Outline LevelFifth Outline LevelSixth Outline Level

Seventh Outline LevelClick to edit Master text styles

Second level

Third level

Fourth level

Fifth level

11/24/15