Acknowledgments
3.4 Functional and Smart Performances and the
3.3.4 Amorphous Polymer/Crystalline Polymer Immiscible Blend
(Polymerization–Diffusion Method) In the case of the immiscible graded blend of the PBMA/PEO system [30], we obtained the optimum conditions in the prepara- tion by the polymerization–diff usion method. Figure 3.18 shows the PEO content of the samples for the direction of thickness, measured by the confocal Raman spectroscopy and the NMR methods. Th e data obtained by the NMR method were almost the same as those by the Raman method. It was found that the NMR method was available and so it was used. Figure 3.19 shows the GPC data of the layers around the thickness points (No. 1, 3, 5, 7 in Figure 3.18) as measured by NMR method. Th e peak cor- responding to the block copolymer (EO-b-BMA copolymer) became larger when the number of the points was larger. Th en, the molecular weight and the content of the block copolymer became larger as the number of points became larger, that is, the BMA content was larger (Table 3.2). It was considered to occur because the polymerization rate was larger with a larger amount of the BMA monomer.
3.4 Functional and Smart
of a graded structure not only suppresses a break at the interface but also gives superior properties compared to the source mate- rials. Th is was considered to occur because the blend phase with the concentration gradient had a suffi ciently high tensile strength. The elongation at break of blend type 2 appeared sufficiently good. Th e tensile modulus of the blend type 2 was higher than that of the blend type 1. It was found that the break in the tensile stress could be suppressed by the formation of a concentration gradient.
3.4.1.2 Thermal Shock Resistance
Th ermal shock resistance tests were performed by moving the specimens from one box to another (kept at 253 and 373 K) repeatedly (fi ve times) every 30 min. Th e specimens were then evaluated for their thermal shock resistance by measuring a maximum angle of warp, as illustrated in Figure 3.20, and adhe- sive strength in shear by tension loading.
Th ermal shock resistance tests of the blend type 2 with the graded structure 2 were performed and the results (maximum value of warp angle and adhesive strength in shear by tension loading) were compared with those of the blend type 1 having the graded structure 1, as shown in Table 3.3.
Th e fi lm of the blend type 1 was highly warped, while that of the blend type 2 did not show any warp. Th e adhesive strength in shear by tension loading of the blend type 2 was higher than that of the blend type 1. Th e reasoning for the above properties was as follows: Th e diff erences in the expansion of the PVC (rubber state) and the PMMA (glass state) at high temperature (395 K) concentrated the warp stress at the interface and decreased the strength of the interface. However, in blend type 2, the phase containing an excellent wide concentration gradient prevented the warp stress from concentrating. Th us, the thermal shock resistance of the blend (blend type 2) with excellent wide con- centration gradient was found to be superior to that of the simi- lar blend (blend type 1) to a laminate fi lm. Th e formation of an excellent wide concentration gradient was found to have improved the strength of the interface.
3.4.1.3 Smart Performance (DMA Properties)
Th e change in tensile storage modulus and tan d of the PVC/
PMMA blend type 2 with a wide concentration gradient around Tg was compared with the perfectly miscible blend (5/5) using the DMA measurement (temperature increasing rate: 1 K/min, frequency: 0.2 Hz). Th e Tg width measurements of storage modu- lus and half temperature of Tg width of tan d were estimated as shown in Table 3.3.
Th e half width of the temperature of tan d for the former (16 K) was signifi cantly larger than that of the latter (10 K). Th us, the blend type 2 was confi rmed to be a continuous phase, having a wide range of Tg.
TABLE 3.2 Molecular Weight and Composition of Several Types of Areas in the PEO/PBMA Functionally Graded Alloy in the Th ickness Direction
Peak 1 Peak 2
Ratio of Peak 1 to Peak 2
No. Mw Mw/Mn Mw Mw/Mn
1 1.39 × 106 2.10 4.33 × 104 1.15 0.38 2 1.40 × 106 2.06 4.61 × 104 1.16 0.37 3 1.80 × 106 2.22 3.93 × 104 1.13 0.94 4 1.69 × 106 2.21 3.69 × 104 1.17 1.04 5 1.79 × 106 2.16 3.80 × 104 1.12 1.15 6 1.58 × 106 2.39 3.84 × 104 1.13 1.27 7 5.66 × 105 2.29 3.34 × 104 1.11 2.68
TABLE 3.3 Properties of PVC/PMMA Functionally Graded Blends
Properties Unit
PVC/PMMA Blend
PVC Only PMMA Only Type 2a Type 1 PMTb
Tensile properties
Tensile strength (kgf/mm2) 6.4 4.5c 7.2 5.7 6.1
Elongation at break (%) 4.5 2.8c 5.2 3.9 3.1
Tensile modulus of elasticity (kgf/mm2) 200 190 220 230 230
DMA properties (tensile mode)
Tg width of storage modulus (K) 20 8.6, 11c 11 — —
Half-temperature width Tg in tan d (K) 16 — 10 — —
Th ermal shock resistance
Maximum warp angle (degree) 9 170d — — —
Adhesive strength in shear by tension loading
(kgf) 98 71d — — —
a Blend containing graded structure 2.
b Perfectly miscible blend.
c Prepared by the hot press method.
d Blend containing graded structure 1.
As a result, tan d of the graded blends of PVC and several types of polyalkyl methacrylate (PMA) containing graded struc- ture 2 were measured, as shown in Figure 3.21. Tan d of the graded PVC/PHMA blend had the widest temperature range.
Th erefore, it was concluded that the wide temperature range was caused by the greater diff erences of Tg in the pair polymers of the graded PVC/PHMA blend.
Finally, we investigated the optimum conditions for prepar- ing the graded PVC/PHMA blend with the wider temperature range of tan d. We obtained a PVC/PHMA blend containing an excellent graded structure 2, which showed a peak of tan d in a
much wider temperature range in comparison with those of the blend containing the graded structure 1 and perfectly miscible blend (5/5), as shown in Figure 3.22.
In both systems of the PVC/PMMA and the PVC/PHMA blends, we found that the tensile storage modulus of the blend type 2 con- tained an excellent graded structure 2 that began to decrease at a lower temperature than that of the perfectly miscible blend (5/5) and did not have a terrace, while that of a similar blend containing the graded structure 1 in a laminate had some terraces.
Sandwich steel beams combining a polymer have been used as damping materials [46]. It is known that the damping effi ciency is maximum in the temperature range at which the used poly- mer has a peak of tan d. Th erefore, it is expected that an excellent graded blend with a peak of tan d in a much wider temperature range is useful as a damping material in a large temperature range. Th is is what the graded polymer blend is expected to be for smart materials. Th e following principle refl ects the reason- ing for this condition for smart materials.
An excellent graded blend was used for the polymer combined with the steel plates, as shown on the right of Figure 3.23. Tg of the graded blend decreases when shift ing occurs from the left to the right side. At the highest temperature, that is, the same tem- perature as the higher Tg of the pair polymers in the blend, the area in the farthest left side shows the highest and best damping performance. As the area shift s to the right side, there is a decrease of temperature. Finally, at the lowest temperature, that is, the same temperature as the lower Tg of the pair polymers in the blend, the area on the farthest right side shows the highest Maximum
angle
FIGURE 3.20 Measurement method of maximum angle of warp.
Increase of tan d
Solution volume 0.455 ml/cm2
DMA
Increase of storage modulus
270 310 350 390
Temperature (K) PVC/PHMA
230
PVC/PHMA PVC/PMMA
PVC/PBMA
PVC/PMMA
PVC/PBMA
FIGURE 3.21 DMA data of PVC/PMA graded blends. FIGURE 3.22 DMA data of PVC/PHMA graded blends.
200 240 280 320 360
Temperature (K) Graded
structure 3 Graded structure 2
Graded structure 1
Increase of tan d
Increase of strage modulus
and best excellent damping performance. Th erefore, the area showing the high damping performance shift s with the chang- ing temperature. Th is performance is thus considered as one of the so-called “smart performances.”
3.4.2 Functional and Smart Performances of PEO/PLLA Graded Blend
PLLA is known as biomass and biodegradable polymer and its bio- degradability was enhanced by blending with PEO. Th us, we pre- pared the PEO/PLLA graded blend, which was expected to have both high biodegradability and tensile strength in the vertical direction of thickness [26]. Th e various types of graded PLLA/
PEO blends, homogeneous blend, and PLLA only were subjected to degradation by a proteinase K enzyme. Th e biodegradability
was evaluated by the net weight loss of PLLA calculated by diff er- ence of weightbefore and aft er testing. Th e net weight loss in all of the graded blends was higher than those in the homogeneous blend and the PLLA only (Figure 3.24). Th e net weight loss of graded blend type 2 with the best excellent graded structure was the highest. Th us, the graded structure was considered to largely increase biodegradability. It was confi rmed by an SEM observation of these materials (Figure 3.25). Th e net weight loss of all the graded blends, where a porous structure formed before the bio- degradation test, did not result in increase to a great extent. It was
Higher temp.
Medium temp.
Lower temp.
Most superior area in damping property at each temperature
Steel plates
Temperature
Most superior area in damping property
FIGURE 3.23 Schematic model of the so-called smart performance in the damping property of steel plate combined with a functionally graded blend.
0 20 40 60 80 100
0 2 4 6 8 10 12
Past time (day)
Weight loss of PLLA (wt%)
Graded blend type 1 Graded blend type 2 Graded blend type 3 PLLA only
Homogeneous blend
FIGURE 3.24 Changes of net weight loss of PLLA in various types of graded blends, homogeneous blend, and PLLA only, in the biodegra- dation test.
Graded blend II Homogeneous blend
Graded blend I
(a) PLLA (b)
(c) (d)
FIGURE 3.25 SEM photograph of the cross-section of the sample aft er biodegradation test for 11 days.
considered as the following: PEO, not only dissolved into water resulting in increasing the surface area attacked by the enzyme, but also, absorbed the PLLA oligomers that acted as acid catalysts of water decomposition and subsequently, it promoted the decompo- sition of PLLA. Furthermore, the strengths of all the graded blends were larger than that of the homogeneous blend (Table 3.4).
Th erefore, it was concluded that the graded structure enhanced the biodegradability while maintaining its high tensile strength.
3.4.3 Functional and Smart Performances of PEO (or PEO/LiOCl4)/PBMA Graded Blend
PEO/PBMA graded blend was prepared by the polymerization–
diff usion method [30]. It was found that the water vapor perme- ability across the graded blend fi lms was diff erent in the PEO
content on the side of the higher pressure of water vapor (humid- ity: 90%) at 313 K. Th us, the permeability of the vapor from the PEO-rich side (direction 1) was always higher than that of the vapor from the PBMA-rich side (direction 2) (Figure 3.26).
Th erefore, it was found that the graded structure could cause anisotropy in the permeability of the water vapor.
(PEO/LiClO4)/PBMA graded blend was prepared using EO-b-BMA block copolymer by the diff usion–dissolution method [28]. Th e change in the elastic modulus of the graded blend in the thickness direction was estimated as shown in Figure 3.27. Th e modulus of the graded blend decreased gradu- ally around 45%, while that of the laminate began to decrease immediately (Figure 3.28). Th us, it was concluded that the graded blend was prevented from its breakaway at the interface TABLE 3.4 Tensile Strength of Several
Types of Materials
Materials Tensile Strength (MPa)
Graded blend 1 2.46
Graded blend 2 3.05
Graded blend 3 3.20
Homogeneous blend 1.78
PLLA only 2.88
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
0 5 10 15 20 25 30
Past time (h)
Permeability of water vapor (g/mh)
Direction 1 Direction 2 2
1
PBMA rich PEO rich
Permeation direction in the graded blend
Test condition: Temp. 313 K, humidity 90%
FIGURE 3.26 Permeability of water vapor of PEO/PBMA graded blend in both types of the thickness directions.
Elastic modulus (mPa) 0 5 10 15 20 25
0 10 20 30 40 50 60 70 80 90 100
D/d (%)
Laminate (2 layers) Graded composite 1 Graded composite 2
FIGURE 3.27 Tensile elastic modulus of several types of materials in the thickness direction (D/d: (Distance from petri glass side)/(thickness of sample) ).
Laminate (2 layers)
10−2
10−6 10−8 10−10
10−120 20 40 60 80 100
10−4 10−2 10−6 10−8 10−10 10−12 10−4 10−2 10−6 10−8 10−10 10−12 10−4
Electric conductivity (S/cm)
Graded blend 1
Graded blend 2
D/d (%)
FIGURE 3.28 Electric conductivity of several types of materials in the thickness direction (D/d: (Distance from petri glass side)/(thickness of sample) ).
by its graded structure. However, all of the electric conductivi- ties of the graded blends and the laminate began to similarly increase immediately around 40%.