Fabio Bignotti | University of Brescia (original) (raw)

Papers by Fabio Bignotti

AIP Conference Proceedings, 2018

Hydrogels with different degrees of hydrophilicity and cross-link densities were synthesized star... more Hydrogels with different degrees of hydrophilicity and cross-link densities were synthesized starting from epoxy monomers and aliphatic amines. Their chemical cross-link density was varied by changing the functionality of monomers or the resin/hardener ratio. Physical cross-links were introduced by incorporating in the polymer network hydrophobic segments, which in aqueous media give hydrophobic interaction. It was shown that the swelling degree, thermosensitivity and mechanical properties of these hydrogels can be easily tailored by changing the concentration and relative amount of physical and chemical cross-links.Hydrogels with different degrees of hydrophilicity and cross-link densities were synthesized starting from epoxy monomers and aliphatic amines. Their chemical cross-link density was varied by changing the functionality of monomers or the resin/hardener ratio. Physical cross-links were introduced by incorporating in the polymer network hydrophobic segments, which in aqueous media give hydrophobic interaction. It was shown that the swelling degree, thermosensitivity and mechanical properties of these hydrogels can be easily tailored by changing the concentration and relative amount of physical and chemical cross-links.

A series of structurally related epoxy resins were prepared as model systems for the investigatio... more A series of structurally related epoxy resins were prepared as model systems for the investigation of the shape memory response, tailoring their thermo-mechanical response and describing their strain evolution under triggering stimuli with a thermo-viscoelastic model. The shape memory behavior on epoxy resin was modeled through the definition of linear viscoelastic parameters, in combination with the general time-temperature reduction scheme. Specifically, this translates into the definition of a hyperelastic response enriched with a Prony series to implement time dependency and a William-Landel-Ferry (WLF) equation to implement temperature dependency. While the hyperelastic response parameters are found with a standard fitting procedure on compression tests, finding the correct parameters for the Prony series might be challenging. For this reason, an ad-hoc optimization process was coded in Mathworks Matlab environment: proper guess values are created and then a chain of constraine...

AIP Conference Proceedings, 2018

Polymer Engineering & Science, 2019

Polymers for Advanced Technologies, 2018

Journal of Applied Polymer Science, 2017

In this research work, biocomposites based on crosslinked particles of sodium polyacrylate, commo... more In this research work, biocomposites based on crosslinked particles of sodium polyacrylate, commonly used as superabsorbent polymer, and poly(l-lactic acid) (PLLA) were developed to obtain superabsorbent thermoplastic products, and to elucidate the role of this type of filler (i.e., polymeric crosslinked particles) on their overall physical-mechanical behavior. Samples prepared by melt-blending components with different ratios showed a biphasic system with a uniform distribution of particles, with diameters up to about 50 μm, within the PLLA polymeric matrix. The polymeric biphasic system, coded PLASA, that is, superabsorbent PLLA, showed excellent swelling properties, demonstrating that crosslinked particles retain their superabsorbent ability even if distributed in a thermoplastic polymeric matrix. The thermal characteristics of the biocomposites evidenced enhanced thermal stability in comparison with neat PLLA and also mechanical properties are markedly modified by addition of crosslinked particles, revealing a regular stiffening effect. Furthermore, in aqueous environments the particles swell and are leached from PLLA matrix generating very high porosity. These new open-pore foams coded PLASAW, that is, PLASA after water treatment, produced in absence of organic solvents and chemical foaming agents, with good physicomechanical properties appear very promising for several applications, for instance in tissue engineering for scaffold production. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45655.

Polymer Engineering & Science, 2017

A series of amine-hardened epoxies were prepared by systematically varying the stoichiometric rat... more A series of amine-hardened epoxies were prepared by systematically varying the stoichiometric ratio and the relative amounts of diepoxide and monoepoxide resin to chemically control the material composition and macromolecular architecture (chain segments flexibility; cross-link density; amounts of dangling groups). Positron Annihilation Lifetime Spectroscopy was used to investigate the free volume associated to the various epoxy formulations, while dynamic-mechanical analysis was employed to investigate their network density and their primary and secondary mechanical relaxations. The mechanical behavior at small and large strain was studied by means of tensile and compression tests. The results pointed out that deviations from the ideal stoichiometric composition and the addition of monoepoxide resins lead to significant room temperature stiffening, together with a reduction of the cross-link density and glass transition temperature. This behavior, phenomenologically associated to antiplasticization, was interpreted according to the specific macromolecular architecture and ascribed to chain mobility hindrance, as revealed by secondary transitions, whereas no significant contribution from the free volume could be evidenced. Furthermore, it was shown that depending on the strain scale and on the corresponding deformational mechanisms, the mechanical response may be differently influenced either by the presence of dangling groups or by the network density. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Polymer Composites, 2016

Novel biodegradable polymeric materials based on protein hydrolysate (Pr.Hyd), derived from waste... more Novel biodegradable polymeric materials based on protein hydrolysate (Pr.Hyd), derived from waste products of the leather industry, and poly(ethylene glycol) diglycidyl ether (PEG) or epoxidized soybean oil (ESO) are obtained and their physico-chemical properties and mechanical behaviour are evaluated. Different processing conditions and the introduction of fillers of natural origin, as saw dust and wood flour, are used to tailor the mechanical properties and the environmental durability of the product. The biodegradable products, which are almost completely manufactured from renewable-based raw materials, look promising for several applications, particularly in agriculture for the additional fertilizing action of Pr.Hyd. To this purpose, tests are carried out to prove the feasibility of novel biodegradable pots and containers by investigating their functionality, their physico-chemical and mechanical behaviour in standard and controlled experimental field conditions, and to follow the assessment of their biodegradation process during plants cultivation in the soil. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

A series of structurally related epoxy resins were prepared as model systems for the investigatio... more A series of structurally related epoxy resins were prepared as model systems for the investigation of the shape memory response, with the aim to assess the possibility of tailoring their thermo-mechanical response and conveniently describing their strain evolution under triggering stimuli with a simple thermoviscoelastic model. The resins formulation was varied in order to obtain systems with controlled glass transition temperature and crosslink density. The shape memory response was investigated by means of properly designed thermo-mechanical cycles, which allowed to measure both the ability to fully recover the applied strain and to exert a stress on a confining medium. The results were also compared with the predictions obtained by finite element simulations of the thermo-mechanical cycle by the employ of a model whose parameters were implemented from classical DMA analysis.

In this work it is shown that hydroxyethylcellulose (HEC) can be employed for preparing macroporo... more In this work it is shown that hydroxyethylcellulose (HEC) can be employed for preparing macroporous polyacrylamide (PAAm) hydrogels with tailored morphology and mechanical properties. By changing the HEC content in the reaction mixture hydrogels with different pore sizes and degrees of interconnectivity can be synthesized. The equilibrium swelling ratio in 0.1 M NaCl increases with the amount of HEC employed. Tensile tests run on equilibrated hydrogels show that these materials behave as rubber-like materials. Their mechanical stiffness decreases regularly as the amount of HEC, and therefore their porosity, is increased. A more complex trend is observed for elongation and stress at break, which display a maximum at intermediate contents of HEC.

The development and understanding of self-healing mechanisms have been investigated in blends of ... more The development and understanding of self-healing mechanisms have been investigated in blends of ionomers (Poly (ethyelene-co-methacrylic acid), sodium & zinc ions)(EMNa & EMZn) containing both elastomers (Epoxidized natural rubbers (ENR) and cis-1, 4-Polyisoprene (PISP)) and crystalline component (Poly (vinly alcohol-co-ethylene)[PVAcE]) as secondary phases. All the blends were prepared by melt-blending and self-healing behavior was studied in ballistic puncture tests. Self-healing behavior of each material ...

Polymer Testing, 2012

The applicability of wire cutting in determining the fracture resistance, G c , of polyacrylamide... more The applicability of wire cutting in determining the fracture resistance, G c , of polyacrylamide (PAAm) hydrogels, with different polymer contents and mechanical stiffness, was investigated. The various gels were synthesized both in the form of cylindrical and bar-shaped samples. Following the experimental scheme proposed in literature for wire cutting, each hydrogel, in the form of cylindrical specimen, was subjected to wire cutting with wires of different diameters. For each hydrogel, G c was also separately measured by more conventional fracture tests on notched specimens prepared from the bar-shaped samples. The results demonstrated that, although G c of the PAAm hydrogels here examined could not be evaluated by the direct application of the simple scheme proposed in literature, wire cutting is a promising approach for the measurement of the fracture resistance of chemical gels with relatively high stiffness, also in consideration of its proven experimental simplicity.

Polymer Engineering & Science, 2007

An examination of results from ambient fathead minnow subchronic toxicity tests identified a comm... more An examination of results from ambient fathead minnow subchronic toxicity tests identified a common characteristic of the tests, which manifests itself as a large among-replicate and between-test variance in survival. The unusual replicate-specific mortality in tests with ambient water appears to be due to pathogenic bacteria or fungi. This finding is based on the following facts: a comparison of survival among replicates in effluents and ambient waters showed that when mean survival was low (40-70%), among-replicate variation for ambient tests was greater than it was for the effluent tests; in 63 tests conducted at three locations over nearly 3 years, treating the water with ultraviolet (UV) light improved survival; a seasonal pattern to survival was present at ambient sites; survival was higher when minnows were separated by using 1 minnow/beaker rather than the standard system of 10 minnows/beaker; and survival tended to be higher in ambient sites contaminated with low levels of chlorine. The existence of the pathogen(s) does not mean that the test cannot be used effectively to assess toxicity of ambient waters; instead, it indicates that factors other than toxicity may need to be taken into consideration when interpreting the results.

Polymer Degradation and Stability, 2001

The thermogravimetric analysis (TGA) of two classes of multi-block copolymers based on poly(d,l-l... more The thermogravimetric analysis (TGA) of two classes of multi-block copolymers based on poly(d,l-lactic-glycolic acid) (PLGA) and diol-terminated poly(e-caprolactone) (PCDT) or poly(ethylene glycol) (PEG) segments is reported. These materials, having the structure of poly(ester-carbonate)s, were synthesized by a chain extension reaction. The influence of the length of PCDT or PEG segments and of the molar ratio of d,l-lactic acid (LA) and glycolic acid (GA) residues on thermal stability in air and nitrogen atmosphere has been investigated. For comparison purposes the degradation behaviour of starting oligomers was also studied. TGA under nitrogen shows two degradation processes that can be ascribed to the PLGA and PCDT or PEG segments, respectively. In addition, the thermal stability increases with the LA content in the PLGA blocks. In the tests run under air two degradation steps have also been observed, though the former occurs in general at higher temperatures.

Polymer, 2000

Polymers capable of responding to both temperature and pH changes were synthesised by radical cop... more Polymers capable of responding to both temperature and pH changes were synthesised by radical copolymerisation of N-isopropylacrylamide (NIPAAm) and N-methacryloyl-l-leucine (MALEU) in different NIPAAm/MALEU molar ratios (15:1, 10:1, 2:1 and 1:1). The polymers were characterised by Size Exclusion Chromatography, acid-base titrations, FT-IR and 1 H-NMR analyses. Their solution behaviour was studied in 0.1 M NaCl and in citrate buffers (pH 4.0, 4.5, 5.0 and 6.0). At pH 4.0 and 4.5 the cloud point temperature (T CP) of copolymers was depressed proportionally to their MALEU content. In contrast, at pH 5.0 and 6.0 the phase transition temperature increased linearly. The behaviour of the copolymers with NIPAAm/MALEU ratios 15:1 and 10:1 was investigated also between pH 3 and 11 in 0.1 M NaCl. In both cases a sharp increase in T CP was observed around pH 4-5. The T CP vs. pH curve was linearised and the acidity constants were determined by the linearisation procedure. Furthermore, it was possible to demonstrate that the phase transition temperature increases linearly with the ionic content of the polymers.

AIP Conference Proceedings, 2018

Hydrogels with different degrees of hydrophilicity and cross-link densities were synthesized star... more Hydrogels with different degrees of hydrophilicity and cross-link densities were synthesized starting from epoxy monomers and aliphatic amines. Their chemical cross-link density was varied by changing the functionality of monomers or the resin/hardener ratio. Physical cross-links were introduced by incorporating in the polymer network hydrophobic segments, which in aqueous media give hydrophobic interaction. It was shown that the swelling degree, thermosensitivity and mechanical properties of these hydrogels can be easily tailored by changing the concentration and relative amount of physical and chemical cross-links.Hydrogels with different degrees of hydrophilicity and cross-link densities were synthesized starting from epoxy monomers and aliphatic amines. Their chemical cross-link density was varied by changing the functionality of monomers or the resin/hardener ratio. Physical cross-links were introduced by incorporating in the polymer network hydrophobic segments, which in aqueous media give hydrophobic interaction. It was shown that the swelling degree, thermosensitivity and mechanical properties of these hydrogels can be easily tailored by changing the concentration and relative amount of physical and chemical cross-links.

A series of structurally related epoxy resins were prepared as model systems for the investigatio... more A series of structurally related epoxy resins were prepared as model systems for the investigation of the shape memory response, tailoring their thermo-mechanical response and describing their strain evolution under triggering stimuli with a thermo-viscoelastic model. The shape memory behavior on epoxy resin was modeled through the definition of linear viscoelastic parameters, in combination with the general time-temperature reduction scheme. Specifically, this translates into the definition of a hyperelastic response enriched with a Prony series to implement time dependency and a William-Landel-Ferry (WLF) equation to implement temperature dependency. While the hyperelastic response parameters are found with a standard fitting procedure on compression tests, finding the correct parameters for the Prony series might be challenging. For this reason, an ad-hoc optimization process was coded in Mathworks Matlab environment: proper guess values are created and then a chain of constraine...

AIP Conference Proceedings, 2018

Polymer Engineering & Science, 2019

Polymers for Advanced Technologies, 2018

Journal of Applied Polymer Science, 2017

In this research work, biocomposites based on crosslinked particles of sodium polyacrylate, commo... more In this research work, biocomposites based on crosslinked particles of sodium polyacrylate, commonly used as superabsorbent polymer, and poly(l-lactic acid) (PLLA) were developed to obtain superabsorbent thermoplastic products, and to elucidate the role of this type of filler (i.e., polymeric crosslinked particles) on their overall physical-mechanical behavior. Samples prepared by melt-blending components with different ratios showed a biphasic system with a uniform distribution of particles, with diameters up to about 50 μm, within the PLLA polymeric matrix. The polymeric biphasic system, coded PLASA, that is, superabsorbent PLLA, showed excellent swelling properties, demonstrating that crosslinked particles retain their superabsorbent ability even if distributed in a thermoplastic polymeric matrix. The thermal characteristics of the biocomposites evidenced enhanced thermal stability in comparison with neat PLLA and also mechanical properties are markedly modified by addition of crosslinked particles, revealing a regular stiffening effect. Furthermore, in aqueous environments the particles swell and are leached from PLLA matrix generating very high porosity. These new open-pore foams coded PLASAW, that is, PLASA after water treatment, produced in absence of organic solvents and chemical foaming agents, with good physicomechanical properties appear very promising for several applications, for instance in tissue engineering for scaffold production. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45655.

Polymer Engineering & Science, 2017

A series of amine-hardened epoxies were prepared by systematically varying the stoichiometric rat... more A series of amine-hardened epoxies were prepared by systematically varying the stoichiometric ratio and the relative amounts of diepoxide and monoepoxide resin to chemically control the material composition and macromolecular architecture (chain segments flexibility; cross-link density; amounts of dangling groups). Positron Annihilation Lifetime Spectroscopy was used to investigate the free volume associated to the various epoxy formulations, while dynamic-mechanical analysis was employed to investigate their network density and their primary and secondary mechanical relaxations. The mechanical behavior at small and large strain was studied by means of tensile and compression tests. The results pointed out that deviations from the ideal stoichiometric composition and the addition of monoepoxide resins lead to significant room temperature stiffening, together with a reduction of the cross-link density and glass transition temperature. This behavior, phenomenologically associated to antiplasticization, was interpreted according to the specific macromolecular architecture and ascribed to chain mobility hindrance, as revealed by secondary transitions, whereas no significant contribution from the free volume could be evidenced. Furthermore, it was shown that depending on the strain scale and on the corresponding deformational mechanisms, the mechanical response may be differently influenced either by the presence of dangling groups or by the network density. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Polymer Composites, 2016

Novel biodegradable polymeric materials based on protein hydrolysate (Pr.Hyd), derived from waste... more Novel biodegradable polymeric materials based on protein hydrolysate (Pr.Hyd), derived from waste products of the leather industry, and poly(ethylene glycol) diglycidyl ether (PEG) or epoxidized soybean oil (ESO) are obtained and their physico-chemical properties and mechanical behaviour are evaluated. Different processing conditions and the introduction of fillers of natural origin, as saw dust and wood flour, are used to tailor the mechanical properties and the environmental durability of the product. The biodegradable products, which are almost completely manufactured from renewable-based raw materials, look promising for several applications, particularly in agriculture for the additional fertilizing action of Pr.Hyd. To this purpose, tests are carried out to prove the feasibility of novel biodegradable pots and containers by investigating their functionality, their physico-chemical and mechanical behaviour in standard and controlled experimental field conditions, and to follow the assessment of their biodegradation process during plants cultivation in the soil. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

A series of structurally related epoxy resins were prepared as model systems for the investigatio... more A series of structurally related epoxy resins were prepared as model systems for the investigation of the shape memory response, with the aim to assess the possibility of tailoring their thermo-mechanical response and conveniently describing their strain evolution under triggering stimuli with a simple thermoviscoelastic model. The resins formulation was varied in order to obtain systems with controlled glass transition temperature and crosslink density. The shape memory response was investigated by means of properly designed thermo-mechanical cycles, which allowed to measure both the ability to fully recover the applied strain and to exert a stress on a confining medium. The results were also compared with the predictions obtained by finite element simulations of the thermo-mechanical cycle by the employ of a model whose parameters were implemented from classical DMA analysis.

In this work it is shown that hydroxyethylcellulose (HEC) can be employed for preparing macroporo... more In this work it is shown that hydroxyethylcellulose (HEC) can be employed for preparing macroporous polyacrylamide (PAAm) hydrogels with tailored morphology and mechanical properties. By changing the HEC content in the reaction mixture hydrogels with different pore sizes and degrees of interconnectivity can be synthesized. The equilibrium swelling ratio in 0.1 M NaCl increases with the amount of HEC employed. Tensile tests run on equilibrated hydrogels show that these materials behave as rubber-like materials. Their mechanical stiffness decreases regularly as the amount of HEC, and therefore their porosity, is increased. A more complex trend is observed for elongation and stress at break, which display a maximum at intermediate contents of HEC.

The development and understanding of self-healing mechanisms have been investigated in blends of ... more The development and understanding of self-healing mechanisms have been investigated in blends of ionomers (Poly (ethyelene-co-methacrylic acid), sodium & zinc ions)(EMNa & EMZn) containing both elastomers (Epoxidized natural rubbers (ENR) and cis-1, 4-Polyisoprene (PISP)) and crystalline component (Poly (vinly alcohol-co-ethylene)[PVAcE]) as secondary phases. All the blends were prepared by melt-blending and self-healing behavior was studied in ballistic puncture tests. Self-healing behavior of each material ...

Polymer Testing, 2012

The applicability of wire cutting in determining the fracture resistance, G c , of polyacrylamide... more The applicability of wire cutting in determining the fracture resistance, G c , of polyacrylamide (PAAm) hydrogels, with different polymer contents and mechanical stiffness, was investigated. The various gels were synthesized both in the form of cylindrical and bar-shaped samples. Following the experimental scheme proposed in literature for wire cutting, each hydrogel, in the form of cylindrical specimen, was subjected to wire cutting with wires of different diameters. For each hydrogel, G c was also separately measured by more conventional fracture tests on notched specimens prepared from the bar-shaped samples. The results demonstrated that, although G c of the PAAm hydrogels here examined could not be evaluated by the direct application of the simple scheme proposed in literature, wire cutting is a promising approach for the measurement of the fracture resistance of chemical gels with relatively high stiffness, also in consideration of its proven experimental simplicity.

Polymer Engineering & Science, 2007

An examination of results from ambient fathead minnow subchronic toxicity tests identified a comm... more An examination of results from ambient fathead minnow subchronic toxicity tests identified a common characteristic of the tests, which manifests itself as a large among-replicate and between-test variance in survival. The unusual replicate-specific mortality in tests with ambient water appears to be due to pathogenic bacteria or fungi. This finding is based on the following facts: a comparison of survival among replicates in effluents and ambient waters showed that when mean survival was low (40-70%), among-replicate variation for ambient tests was greater than it was for the effluent tests; in 63 tests conducted at three locations over nearly 3 years, treating the water with ultraviolet (UV) light improved survival; a seasonal pattern to survival was present at ambient sites; survival was higher when minnows were separated by using 1 minnow/beaker rather than the standard system of 10 minnows/beaker; and survival tended to be higher in ambient sites contaminated with low levels of chlorine. The existence of the pathogen(s) does not mean that the test cannot be used effectively to assess toxicity of ambient waters; instead, it indicates that factors other than toxicity may need to be taken into consideration when interpreting the results.

Polymer Degradation and Stability, 2001

The thermogravimetric analysis (TGA) of two classes of multi-block copolymers based on poly(d,l-l... more The thermogravimetric analysis (TGA) of two classes of multi-block copolymers based on poly(d,l-lactic-glycolic acid) (PLGA) and diol-terminated poly(e-caprolactone) (PCDT) or poly(ethylene glycol) (PEG) segments is reported. These materials, having the structure of poly(ester-carbonate)s, were synthesized by a chain extension reaction. The influence of the length of PCDT or PEG segments and of the molar ratio of d,l-lactic acid (LA) and glycolic acid (GA) residues on thermal stability in air and nitrogen atmosphere has been investigated. For comparison purposes the degradation behaviour of starting oligomers was also studied. TGA under nitrogen shows two degradation processes that can be ascribed to the PLGA and PCDT or PEG segments, respectively. In addition, the thermal stability increases with the LA content in the PLGA blocks. In the tests run under air two degradation steps have also been observed, though the former occurs in general at higher temperatures.

Polymer, 2000

Polymers capable of responding to both temperature and pH changes were synthesised by radical cop... more Polymers capable of responding to both temperature and pH changes were synthesised by radical copolymerisation of N-isopropylacrylamide (NIPAAm) and N-methacryloyl-l-leucine (MALEU) in different NIPAAm/MALEU molar ratios (15:1, 10:1, 2:1 and 1:1). The polymers were characterised by Size Exclusion Chromatography, acid-base titrations, FT-IR and 1 H-NMR analyses. Their solution behaviour was studied in 0.1 M NaCl and in citrate buffers (pH 4.0, 4.5, 5.0 and 6.0). At pH 4.0 and 4.5 the cloud point temperature (T CP) of copolymers was depressed proportionally to their MALEU content. In contrast, at pH 5.0 and 6.0 the phase transition temperature increased linearly. The behaviour of the copolymers with NIPAAm/MALEU ratios 15:1 and 10:1 was investigated also between pH 3 and 11 in 0.1 M NaCl. In both cases a sharp increase in T CP was observed around pH 4-5. The T CP vs. pH curve was linearised and the acidity constants were determined by the linearisation procedure. Furthermore, it was possible to demonstrate that the phase transition temperature increases linearly with the ionic content of the polymers.