Rigid Amorphous Phase Research Articles

The effect of thermal history on crystalline structure and mechanical properties of β-nucleated isotactic polypropylene

The effect of thermal history on β-nucleated iPP was systematically investigated by comparing the variance of crystalline microstructures and mechanical property of stepwise crystallized sample and annealed sample, which experienced different thermal history. The mechanical property tests exhibit that that the toughness of stepwise crystallized sample and annealed sample were both decreased compared to control sample, while the tensile strength of the stepwise crystallized sample increased slightly. Structure investigation showed that the α-relaxation peak, which is related to the assignment of chains in rigid amorphous phase, moved to the high temperature region for stepwise crystallized sample, while it moved to the low temperature region for annealed sample. The results indicated the weakening in rigid amorphous fraction (RAF) and the increase in lamellar thickness of β-iPP after stepwise crystallization treatment. For annealed sample, the RAF strengthened and lamellar thickness decreased slightly after thermal treatment. A mechanism of crystalline microstructures evolution of restricted area between the main lamellar under different treatments was proposed.

Fundamental thermal properties of polyvinyl alcohol by fast scanning calorimetry

Polyvinyl alcohol (PVA) is a synthetic, semi-crystalline polymer with a wide array of commercial uses ranging from textiles and packaging to medicine. Despite the fact that PVA is in common use, several important thermal properties have not been measured including: 1. temperature dependent liquid state specific heat capacity, cpLiquid(T); 2. specific heat capacity increment of amorphous PVA at the glass transition temperature, Δcpamor(Tg); and, 3. fraction of rigid amorphous phase in semi-crystalline PVA, ϕRA. Two rate-dependent effects have prevented these measurements: PVA thermally degrades at temperatures just in excess of 200 °C which is often within the onset of melting, and PVA crystallizes from the melt so rapidly that it is difficult to obtain fully amorphous polymer. To prevent degradation, and measure these fundamental thermal properties, we have used fast scanning calorimetry at rates ranging from 1000 K/s up to 600,000 K/s. The Mettler Flash DSC1 and a custom-built calorimeter were used to cover this range of heating and cooling rates. We determine the critical cooling rate, βc, needed to quench PVA into an amorphous glass as |βc| = 20,000 K/s. Using FSC in combination with conventional differential scanning calorimetry, we find cpLiquid(T) = ((0.0016 ± 0.0002)*T + (2.3 ± 0.2)) J/(gK). The specific heat capacity increment for fully amorphous PVA is Δcpamor(Tg) = (1.01 ± 0.05) J/(gK). For the semi-crystalline samples used in this study, PVA obeys a two phase model in which ϕRA ∼0. The approaches used in this work are applicable to any semicrystalline polymer or biopolymer which degrades upon heating, or crystallizes so rapidly from the melt that a fully amorphous material cannot be realized.

Investigation of Structure and Crystallization Behavior of Poly(butylene succinate) by Fourier Transform Infrared Spectroscopy.

The detailed structure and crystallization behavior of poly(butylene succinate) (PBS) have been investigated by Fourier transform infrared (FTIR) and other methods systematically. For the first time, we confirmed that the C═O stretching modes of PBS can respond to three distinguish absorption bands in the FTIR spectrum, at around 1736, 1720, and 1714 cm-1 respectively. The 1736 cm-1 band is adopted as the stretching mode of C═O groups in free amorphous fraction (MAF); the 1714 cm-1 band which is relevant to more stable structure, displays more anisotropic in polarized FTIR spectra, and has been confirmed as stretching vibrations of hydrogen-bonded C═O groups in the crystalline phase. The 1720 cm-1 band is linked to crystallization but comes from less ordered structure. Moreover, the 1720 cm-1 band can be destroyed prior to 1714 cm-1 band during heating and constructed behind 1714 cm-1 band during cooling. Thus, the 1720 cm-1 band is reasonably ascribed to the C═O groups in rigid amorphous fraction (RAF) or intermediate phase which locates between MAF and crystalline phase. The corresponding investigation by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) further supports that the three particular C═O absorption bands indeed reveal the typical three-phase structure for PBS. More important, the FTIR spectrum of PBS is very sensitive to sample preparation process and measurement mode. The relative content of each band depends on the crystallization temperature (Tc) and measured thickness. The higher Tc, the more RAF content appears when measured at room temperature; the thinner penetration thickness of FTIR measurement, the less RAF content can be detected, and the penetration thickness-dependent behavior is suggested as the result of higher mobility of chains in the air/bulk surface. Additionally, the particular three absorption bands of C═O groups in PBS force us to carefully reconsider previous reports on structure and interaction state obtained by FTIR spectroscopy in PBS and its composites.

Glass transition temperature versus structure of polyamide 6: A flash-DSC study

The glass transition temperature (Tg) is a crucial parameter for understanding the mechanical behavior of polyamide 6. It depends mainly on two aspects: hydration level and processing, i.e. the thermal history and the flow conditions. In this work, the effect of the thermal history on Tg was investigated by means of fast scanning calorimetry (flash-DSC). Two different solidification procedures were studied; isothermal crystallization and continuous cooling were performed at different temperatures and rates respectively. The procedures have led to two contradictory trends of glass transition evolutions when related to their crystallinity fraction. The concept of rigid amorphous phase is used. This is considered as a part of the amorphous phase with a lower mobility, present at the inter-phase between crystals and bulk amorphous (mobile amorphous fraction). The analysis leads to the conclusion that the thermal history affects the ratio between rigid and mobile amorphous phases and it is this ratio that determines the glass transition temperature of dry polyamide 6.

Rigid Amorphous Phase: Mechanical and Transport Properties of Nitrile Rubber/Clay Nanocomposites

The present study has been focused on the preparation of nitrile rubber/ organoclay nanocomposites containing 0–10 wt% Cloisite 93A by mechanical mixing on a two-roll mill. The rubber samples were vulcanized by accelerated sulfur vulcanization process. The role of nanoclay on the curing process has been carefully studied. The clay dispersion in the rubber matrix was analyzed by high resolution transmission electron microscopy (TEM) and X-ray diffraction studies. Both XRD and electron microscopic analyses indicated that the nanocomposites exhibit partly intercalated and exfoliated structure. However, the nanocomposites showed better exfoliation at lower clay loading (2 wt percent) as evident by TEM and XRD. At higher clay loading the clay tend to form aggregates. The correlation distance and the length and thickness of the clay platelets in the rubbery matrix have been deduced from the TEM micrographs as a function of clay loading. The nanoclay-rubber interaction has been quantified by Kraus analysis. The nanocomposites exhibited improved mechanical properties which include tensile strength, modulus, tear strength and resistance to abrasion. The solvent resistance of the nanocomposite increased with the increase in dosage of the nanofiller. Finally, the properties have been modeled using Guth and Halpin-Tsai equations.

Effect of Chain Dynamics, Crystallinity, and Free Volume on the Barrier Properties of Poly(ethylene terephthalate) Biaxially Oriented Films

The primary focus of this work was to evaluate the relationship between free volume distribution, chain motion, crystallinity, and the gas properties of PET upon strain-induced crystallization (SIC) at different stretch ratios. The formation of a three-phase structure containing rigid amorphous phase, mobile amorphous phase, and crystalline phase upon SIC was confirmed by differential scanning calorimetry and positron annihilation lifetime spectroscopy (PALS). Dynamic mechanical analysis and PALS indicated that there was a significant reduction in the fractional free volume upon orientation at an extension ratio of 3 × 3. Sub-Tg relaxation studies indicated that the activation energy of mechanical relaxation decreased with increasing the stretch ratio. Gas transport studies revealed that the reduction in permeability coefficient was mainly due to reduction in diffusivity. Permeation studies using gas molecules with different sizes revealed that strain-induced crystallization affects the free volume distri...

Ethylene brassylate: Searching for new comonomers that enhance the ductility and biodegradability of polylactides

Copolymers based on d,l-lactide (D,L-LA) and ethylene brassylate, with EB molar contents ranging from 3 to 39%, were synthesized by ring-opening polymerization at 130 °C using triphenyl bismuth. The poly (D,L-LA-co-EB) presented a random distribution of sequences (R→1), resulting in a fully amorphous structure with TgS between −17 and 43 °C that exhibited upgraded thermal stability and a final degradation temperature of ∼450°, which was approximately 100 °C higher than that observed for PDLLA. The incorporation of EB led to mechanical behaviour with improved flexibility and ductility, compared to polylactides. Moreover, the impact was greater than that provided by other monomers such as ε-caprolactone or δ-valerolactone. A macrolactone molar content of only 5% was enough to increase the elongation at break from 2 to 87% but its elastic modulus remained around 1 GPa, whereas the copolymer with 16% EB (Tg at 17 °C) displayed a clear elastomeric curve with secant modulus of 2.0 MPa and a tensile strength of 0.3 MPa at 1400% of strain (when the specimens did not break). Likewise, the disordered chain microstructure distribution of these copolymers with short sequence lengths of L-LA, D-LA and EB allowed high degradation rates (KMw) in the range of 0.055–0.062 per day, with a maximum KMw for the copolyester containing 9% of EB. In contrast, PDLLA and the 97:3 D,L-LA-co-EB copolymer, owing to their high resistance to water uptake and their packed and rigid amorphous phase, showed degradation velocities of only 0.012 and 0.021 per day, values that are slightly higher than that of poly (l-lactide) whose rate is 0.011 per day.

Crystallization behavior of nanocomposites based on poly(l-lactide) and MgAl layered double hydroxides – Unbiased determination of the rigid amorphous phases due to the crystals and the nanofiller

Semicrystalline polymers have to be described by a three phase model consisting of a mobile amorphous (MAF), a crystalline (CF), and a rigid amorphous fraction (RAF). For nanocomposites based on a semicrystalline polymer the RAF is due to both the crystallites (RAFcrystal) and the filler (RAFfiller). Polymer nanocomposite based on poly(l-lactide) and MgAl layered double hydroxide nanofiller were prepared. Due to the low crystallization rate of PLA its crystallization can be suppressed by a high enough cooling rate, and the RAF is due only to the nanofiller. The MAF, CF, and RAF were estimated by Temperature Modulated DSC. For the first time CF, MAF, RAFcrystal, and RAFfiller could be estimated. It was found, that RAFfiller increases linearly with the concentration of the nanofiller for this system. Furthermore, RAFcrystal is only slightly influenced by the presence of the nanofiller.

Effects of Interphase Modification and Biaxial Orientation on Dielectric Properties of Poly(ethylene terephthalate)/Poly(vinylidene fluoride-co-hexafluoropropylene) Multilayer Films.

Recently, poly(vinylidene fluoride) (PVDF)-based multilayer films have demonstrated enhanced dielectric properties, combining high energy density and high dielectric breakdown strength from the component polymers. In this work, further enhanced dielectric properties were achieved through interface/interphase modulation and biaxial orientation for the poly(ethylene terephthalate)/poly(methyl methacrylate)/poly(vinylidene fluoride-co-hexafluoropropylene) [PET/PMMA/P(VDF-HFP)] three-component multilayer films. Because PMMA is miscible with P(VDF-HFP) and compatible with PET, the interfacial adhesion between PET and P(VDF-HFP) layers should be improved. Biaxial stretching of the as-extruded multilayer films induced formation of highly oriented fibrillar crystals in both P(VDF-HFP) and PET, resulting in improved dielectric properties with respect to the unstretched films. First, the parallel orientation of PVDF crystals reduced the dielectric loss from the αc relaxation in α crystals. Second, biaxial stretching constrained the amorphous phase in P(VDF-HFP) and thus the migrational loss from impurity ions was reduced. Third, biaxial stretching induced a significant amount of rigid amorphous phase in PET, further enhancing the breakdown strength of multilayer films. Due to the synergistic effects of improved interfacial adhesion and biaxial orientation, the PET/PMMA/P(VDF-HFP) 65-layer films with 8 vol % PMMA exhibited optimal dielectric properties with an energy density of 17.4 J/cm(3) at breakdown and the lowest dielectric loss. These three-component multilayer films are promising for future high-energy-density film capacitor applications.

Isothermal crystallization and structural characterization of poly(ethylene-2,5-furanoate)

Among “green” alternatives for oil-based commodity plastics like Polyethylene, Polyamides, and Poly(Ethylene Terephthalate), a new class of polyesters synthesized from furandicarboxylic acids (FDCAs) currently is in the spotlight of both the academic and industrial communities. Of particular interest is Poly(Ethylene-2,5-Furanoate) (PEF), which can be synthesized from monomers derived from sugars and exhibits physical properties that imply large substitution potential for PET in bottle, fiber and packaging applications. In this study the structure-thermal properties relationship of PEF have been investigated in order to explain the complex behavior exhibited by PEF during isothermal crystallization. Secondary crystallization and melt-recrystallization processes have been identified in order to explain the observed behavior. The existence of a critical crystallization temperature around 170 °C marking a transition in terms of crystalline phase induced is also pointed out. Moreover, data such as the molecular weight between entanglements (Me) and standard melting enthalpy (ΔHm°) have been determined. In addition the crystalline morphology was characterized by means of SAXS and WAXS. The influence of the crystallization conditions on this morphology is given. As a main result it has been found that depending on the crystallization temperature (Tc), a disordered or an ordered crystalline phase (called α′ and α respectively) are formed at low (Tc ≤ 170 °C) and high (Tc ≥ 170 °C) temperatures, respectively. Finally, evidence for the formation of a rigid amorphous phase during crystallization is presented, indicating that a three-phase model has to be considered in order to provide an appropriate description of the morphology in semi-crystalline PEF.

Space charge and dipolar charge contribution at polar polymers polarization

The thermally stimulated discharge current, the final thermally stimulated discharge current, DC conductivity and the final thermally stimulated discharge current with partially blocking electrode measures were used to analyze electrical behavior of Nylon 11. The objective was to discriminate between dipole related effects and space charge related effects. The space charge effects are dominant in the temperature range from room temperature to 170 °C. By using a Teflon-FEP partially blocking electrode, the space charge injected in the sample is diminished and the effects related to dipole movement can be observed. Beside the two known relaxations for Nylon 11, one associated with the glass transition around 60 °C and a second one associated with a molecular motion in the rigid-amorphous phase at 96 °C, a weak relaxation was observed around 168 °C. The peak around 96 °C is quite broad been composed of two narrow peaks. The final thermally stimulated discharge current method allows a better selection of the experimental conditions for sample charging (polarization) to have only a partial overlap between the nearby peaks. The peak's maximum current and temperature are dependent on the ratio between the charging and discharging time and temperature given a possibility to discriminate between dipolar and space charge effects. A pyroelectric current changes sign around 140 °C indicating that the amidegroup dipoles are frozen in opposite directions when the sample temperature is below 140 °C (amorphous and rigid-amorphous phase) or above (crystalline phase). The conductivity is controlled by the competition between n(E,T) and μ(E,T) indicating a space charge controlled conductivity mechanism.

Biocomposites based on poly(lactic acid) and seaweed wastes from agar extraction: Evaluation of physicochemical properties

ABSTRACTSeaweed waste (SWW) is a residue or by‐product from the filtration step of the agar extraction process, and it has been explored as an inexpensive and effective filler for incorporation by melt blending into a poly(lactic acid) (PLA) matrix. PLA‐SWW biocomposites were manufactured with various contents of SWW (0, 5, 10, 15, and 20 wt %) using a sheet extrusion process. PLA was functionalized with maleic anhydride (MAH) by reactive extrusion using dicumyl peroxide (DCP) as an initiator, and it was extruded using 0, 5, and 20 wt %. SWW content. The mechanical, thermal, structural, and morphological properties of the processed biocomposites were investigated. Regarding the mechanical behavior, a slight increase in the tensile modulus was observed at low SWW content. The thermal properties indicated that the rigid amorphous phase content was enhanced in the biocomposites. This work suggests that SWW can be used as filler to develop environmental friendly biocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42320.

A thermodynamic approach to model the caloric properties of semicrystalline polymers

It is well known that the crystallisation and melting behaviour of semicrystalline polymers depends in a pronounced manner on the temperature history. If the polymer is in the liquid state above the melting point, and the temperature is reduced to a level below the glass transition, the final degree of crystallinity, the amount of the rigid amorphous phase and the configurational state of the mobile amorphous phase strongly depend on the cooling rate. If the temperature is increased afterwards, the extents of cold crystallisation and melting are functions of the heating rate. Since crystalline and amorphous phases exhibit different densities, the specific volume depends also on the temperature history. In this article, a thermodynamically based phenomenological approach is developed which allows for the constitutive representation of these phenomena in the time domain. The degree of crystallinity and the configuration of the amorphous phase are represented by two internal state variables whose evolution equations are formulated under consideration of the second law of thermodynamics. The model for the specific Gibbs free energy takes the chemical potentials of the different phases and the mixture entropy into account. For simplification, it is assumed that the amount of the rigid amorphous phase is proportional to the degree of crystallinity. An essential outcome of the model is an equation in closed form for the equilibrium degree of crystallinity in dependence on pressure and temperature. Numerical simulations demonstrate that the process dependences of crystallisation and melting under consideration of the glass transition are represented.

Electrospinning of Nylon11: Effect of processing parameters on morphology and microstructure

In this work we have described the influence of electrospinning parameters on the morphology of Nylon11 electrospun mats and the microstructure of the fibers constituting the mats. Specifically, we have investigated the effects of solution concentration, applied voltage and distance between the electrodes on the diameter and shape of the nanofibers. Various techniques were used to characterize the microstructure of the Nylon11 electrospun nanofibers and the same was compared with the structure of melt pressed and solution cast films of Nylon11. We show that rapid formation of electrospun nanofibers causes the Nylon11 chains to crystallize in the metastable gamma phase and show lower degree of crystallinity. Further, the fibers show higher glass transition temperature and higher activation energy for the glass-to-rubber transition suggesting the possibility of a rigid amorphous phase. Finally, we have carried out comparative evaluation of electrospun Nylon11 mats and solution cast/melt pressed films for culturing HEK293 cells.

Mechanical and thermal property characterization of poly-l-lactide (PLLA) scaffold developed using pressure-controllable green foaming technology.

Poly-l-lactide (PLLA) is one of the most promising biological materials used for tissue engineering scaffolds (TES) because of their excellent biodegradability and tenability. Here, microcellular PLLA foams were fabricated by pressure-controllable green foaming technology. Scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), wide angle X-ray diffraction measurement (WAXRD), thermogravimetric (TG) analysis, reflection-Fourier transform infrared (FTIR) analysis, enzymatic degradation study and MTT assay were used to analyze the scaffolds' morphologies, structures and crystallinities, mechanical and biodegradation properties, as well as their cytotoxicity. The results showed that PLLA foams with pore sizes from 8 to 103μm diameters were produced when the saturation pressure decreased from 7.0 to 4.0MPa. Through a combination of StepScan DSC (SSDSC) and WAXRD approaches, it was observed in PLLA foams that the crystallinity, highly-oriented metastable state and rigid amorphous phase increased with the increasing foaming pressure. It was also found that both the glass transition temperature and apparent enthalpy of PLLA significantly increased after the foaming process, which suggested that the changes of microcellular structure could provide PLLA scaffolds better thermal stability and elasticity. Moreover, MTT assessments suggested that the smaller pore size should benefit cell attachment and growth in the scaffold. The results of current work will give us better understanding of the mechanisms involved in structure and property changes of PLLA at the molecular level, which enables more possibilities for the design of PLLA scaffold to satisfy various requirements in biomedical and green chemical applications.

New eco-friendly random copolyesters based on poly(propylene cyclohexanedicarboxylate): Structure-properties relationships

A series of novel random copolymers of poly(propylene 1,4-cyclohexanedicarboxylate) (PPCE) containing neo - pentyl glycol sub-unit (P(PCExNCEy)) were synthesized and characterized in terms of molecular and solid-state properties. In addition, biodegradability studies in compost have been conducted. The copolymers displayed a high and similar thermal stability with respect to PPCE. At room temperature, all the copoly- mers appeared as semicrystalline materials: the main effect of copolymerization was a lowering of crystallinity degree (!c) and a decrease of the melting temperature compared to the parent homopolymer. In particular, Wide Angle X-Ray diffrac- tion (WAXD) measurements indicated that P(PCExNCEy) copolymers are characterized by cocrystallization, PNCE co- units cocrystallizing in PPCE crystalline phase. Final properties and biodegradation rate of the materials under study were strictly dependent on copolymer composition and !c. As a matter of fact, the elastic modulus and the elongation at break decreased and increased, respectively, as neopentyl glycol cyclohexanedicarboxylate (NCE) unit content was increased. The presence of a rigid-amorphous phase was evidenced by means of Dynamic Mechanical Thermal Analysis (DMTA) analysis in all the samples under investigation. Lastly, the biodegradation rate of P(PCExNCEy) copolymers was found to slightly increase with the increasing of NCE molar content.

Transition of the bounded polymer layer to a rigid amorphous phase: A computational and DSC study

The study focuses on the transition of the bounded to solid surfaces polymer layer to a rigid amorphous phase (RAP). Based on previous Monte Carlo (MC) simulation studies on bulk polyethylene (PE), we refine our numerical variable density Self Consistent Field (nSCF) method in order the calculated density in bulk to follow the predictions of the MC simulation. The proposed modification of the Sanchez–Lacombe equation of state allows us to examine thermodynamic aspects of the glass transition. By imposing a glass transition (Tg = 220 K) in the bulk we predict an earlier (during cooling), stronger transition of the bounded layer to a RAP, at ∼350 K. Also at short separation distances we record the appearance of undisturbed polymer bridges. Differential scanning calorimetry (DSC) experiments on polydimethylsiloxane (PDMS) and polyamide 6 (PA6) nanocomposites suggest that although the crystallization can be significantly suppressed by the addition of nanoparticles, the RAP layer may locally equilibrate, above Tg, for long experimental times with the melt phase. Our results support the idea that a significant free energy barrier of entropic origin appears due to the RAP formation, below the melting temperature (Tm) and above the Tg.

Relaxation dynamics and cold crystallization of poly(pentamethylene terephthalate) as revealed by dielectric spectroscopy

The relaxation dynamics of poly(pentamethylene terephthalate) has been investigated by means of dielectric spectroscopy. The sub-glass dynamics is characterized by the existence of a bimodal β process whose faster and slower components have been assigned to the relaxation of the bond between the ester oxygen and the aliphatic carbon and to the link between the aromatic ring carbon and the ester carbon, respectively. By comparison with other closely related aromatic polyesters it is shown that the faster component strongly depends on the amount of methylene groups while the slower one is not considerably affected by the nature of the glycol subunit. The changes in the α process associated to the segmental relaxation during cold crystallization reveal the formation of a rigid amorphous phase fraction. Combination of dielectric experiments with X-ray scattering ones suggests that during cold crystallization PPT crystal lamellae tend to fill the space homogeneously.

13C Solid State NMR Characterization of Structure and Orientation Development in the Narrow and Broad Molar Mass Disentangled UHMWPE

The ultimate draw ratio in semicrystalline polymers, and the resultant mechanical properties of the polymer, strongly depends on entanglement density in the amorphous region of the polymer. The influence of entanglement density becomes more pronounced with the increasing molar mass, for an example in the ultrahigh molecular weight polyethylene (UHMW-PE, having weight-average molar mass greater than a million g/mol) the solid-state deformation (draw ratio >7) is feasible on crystallization of the polymer from dilute solution or during controlled polymerization using a single-site catalytic system. Here we address the influence of the molar mass distribution, associated with the polymerization conditions, on structural changes during solid-state deformation in the crystalline and the noncrystalline regions of UHMW-PE. With the help of various solid state NMR methods, differences in the deformation behavior of the mobile-amorphous, rigid-amorphous, and crystalline polymorphs have been followed in the broad and narrow molar mass UHMW-PEs. Orientation parameters arising at the segmental length scales, within different regions of the semicrystalline polymers, have been addressed. 2D 13C exchange NMR methods have been employed to follow the spatial proximity between the methylene segments of the noncrystalline regions (mobile- and rigid-amorphous phases) with the crystalline regions (crystalline core and crystal surface) during deformation of the two polymers. Distinct differences in the orientation parameters of the methylene segments in the noncrystalline and the crystalline regions, arising with the deformation of the broad and the narrow molar mass distributed UHMW-PE, have been observed and addressed.

Towards high-performance polypropylene and its random copolymer: Insight into toughening mechanism of supercritical carbon dioxide assisted annealing

A supercritical carbon dioxide (scCO2) assisted annealing technique is adopted to toughen polypropylene (PP) and its random copolymer with 3.8 wt% co-monomer content (PPR). By using this technique, PP with 4-time improvement in toughness or PPR with superior toughness are obtained. Meanwhile, the stiffness of the materials could be maintained. To understand the toughening mechanism, scanning electron microscope, wide angle X-ray diffraction, calorimetry, dynamic mechanical analysis and small angle X-ray scattering characterizations are carried out. It is demonstrated that the toughening mechanism is strongly related to the microstructure evolutions, including decreased chain density in the mobile amorphous phase, improved crystalline phase and improved rigid amorphous phase after annealing. These microstructure changes could result in higher cavitation ability and diminish inner stress in the amorphous phase, which consequently favors improvement in toughness.