Gennaro Scarinzi

Rubber toughened polybutylene terephthalate: influence of processing on morphology and impact properties

Abstract The toughening of polybutylene terephthalate (PBT) was achieved by adding to it a functionalized ethylene-propylene (EPR) random copolymer. Maleic anhydride molecules, inserted onto the rubber backbone, provided the functionalized sites with which the terminal PBT hydroxide groups could react. A graft copolymer made from an EPR backbone and by PBT branches acted as an interfacial agent between the matrix and the rubbery dispersed phase. The intensity of mixing, represented by the roller speed of the mixing equiment, was varied from 4 to 64 rpm. The morphological features as well as the mechanical impact performance improved with increasing the roller speed up to a value of 48 rpm. Beyond such a value the situation was reversed due to the mechanical degradation of the molten PBT. This induced a diminished internal interconnection of the matrix and hence a worse impact resistance. Dynamic mechanical analysis proved to be a very sensitive tool to detect the presence of interzones existing between the PBT matrix and the EPR rubbery particles. The extension of such zones represents the adhesion between the two components and was also detected by Charpy impact tests.

Role of degree of grafting of functionalized ethylene-propylene rubber on the properties of rubber-modified polyamide-6

An amorphous random ethylene-propylene rubber (EPR) copolymer and EPR-g-succinic anhydride (EPR-g-SA) graft copolymer have been used as rubbery components to obtain binary polyamide (PA6)EPR or PA6EPR-g-SA and ternary PA6/EPR/EPR-g-SA blends by melt mixing. The influence of degree of grafting (DG) or EPR-g-SA on the morphology and tensile and impact properties of such blends has been investigated. Finer and more homogeneous dispersions of the rubbery domains and better impact properties are obtained with increasing degree of grafting in the blends. At equal DG values and for the compositions used, the binary PA6EPR-g-SA alloys show better behaviour than the ternary ones. These results are related to the presence of an (EPR-g-SA)-g-PA6 graft copolymer formed during melt mixing, which acts as an interfacial and emulsifying agent.

Tensile properties and impact behaviour of poly(D(−)3-hydroxybutyrate)/rubber blends

A random ethylene-propylene rubber copolymer with functional ester or anhydride groups and an ethylene vinilacetate copolymer modified by a partial transformation of acetate groups in alcoholic groups were used as minor components to obtain binary poly(D(-)3-hydroxy-butyrate) blends by melt-mixing. The influence of the rubbery impact modifier on the morphology and on the tensile and high-speed fracture behaviour of such blends was investigated. Better properties were found when anhydride groups were present on the rubbery component. This was attributed to chemical interactions occurring between the dispersed phase and the matrix during the blending process.

Rubber modification of polyamide 6 during caprolactam polymerization: influence of composition and functionalization degree of rubber

Abstract Rubber-modified polyamides 6 (PA 6) were obtained directly during the hydrolytic polymerization of e-caprolactam (CL). An ethylene-propylene elastomer (EPR) and dibutyl succinate grafted EPRs (EPR-g-DBS) were used as rubbery components to yield binary PA 6/EPR-g-DBS and ternary PA 6/EPR-g-DBS blends having about 20% by weight of total rubber. Model reactions and selective extractions of the blends indicated that (EPR-g-DBS)-g-PA 6 copolymers are formed during the CL polymerization. The influence of the grafting degree of EPR-g-DBS and, for ternary blends, of the weight ratio EPR/EPR-g-DBS on the morphology and on the impact properties of the blends was also investigated. A finer and more homogeneous dispersion of rubbery domains has been found for binary blends, while ternary blends exhibit a quasi-bimodal distribution of rubbery domains. The impact properties of ternary blends are enhanced with the increase of the relative amount of functionalized rubber. The dependence of the morphological features and of the impact properties on the functionalization degree is more complex. Straightforward correlations between mode and state of dispersion of rubber domains and impact properties were not found.

Rubber modification of polyamide-6 effected concurrently with caprolactam polymerization: influence of blending conditions and degree of grafting of rubber

Abstract Blends of polyamide-6 and functionalized ethylene-propylene rubber (EPR) copolymers were obtained concurrently with the hydrolytic polymerization of caprolactam. It was found that both the degree of grafting of EPR and the time at which the rubber is added during the polymerization reaction of caprolactam play an important role in determining the mode and state of dispersion of the rubbery component and thus the impact behaviour of the material.

From biowaste to bioresource: Effect of a lignocellulosic filler on the properties of poly(3-hydroxybutyrate)

A lignin-rich residue (LRR) obtained as a by-product from the fermentative bioethanol production process, and commercial alkali lignin (AL), were used as fillers for the preparation of bio-based blends and composites with poly(3-hydrobutyrate) (PHB). Chemical characterization of LRR demonstrated that the filler contained sugar residues. Rheological and thermal characterization of the blends demonstrated that LRR did not affect thermal stability of PHB, while AL had a strong pro-degrading effect. Addition of suitable amounts of LRR dramatically affected the rheological behavior of the polymer melt, suggesting that the additive can modify polymer processability. LRR was also a heterogeneous nucleating agent, potentially able to control the physical aging of PHB. Lower resilience and elongation at break values were found for the biocomposites, due to the poor interfacial adhesion between filler and matrix. Biodegradation behavior of the composites was qualitatively assessed by analyzing the surface of soil buried films. Significant surface degradation was observed for PHB, while the process was retarded at high filler concentration, as LRR inhibited hydrolytic and biotic polymer degradation. The reported results demonstrated the feasibility of the conversion of an agro-industrial by-product into a bio-resource in an environmentally friendly and cost-effective way.

Molecular and mechanical characterization of reactive ethylene-propylene elastomers and their use in PA6-based blends

Abstract The nature of the molecular interactions occurring in an ethylene-propylene copolymer functionalized by succinic anhydride groups has been investigated by using FTi.r. spectroscopy. Hydrogen bonding interactions between carboxylic acid units and between carboxylic acid and anhydride groups have been identified. The mechanical tensile properties of such modified elastomers have been investigated and interpreted in terms of the molecular interactions detected spectroscopically. Finally, the effectiveness of these functionalized rubbers as toughening agents for polyamide-6 has also been examined.

Effect of natural phenolics on the thermal and processing behaviour of poly(3-hydroxybutyrate)

Poly(3-hydroxybutyrate) (PHB) is a biodegradable polymer, whose applicability is limited by its relatively poor mechanical properties and narrow processing window. In this paper, different natural phenol-based additives, including tannic acid (TA), grape bagasse extract (EP), and a lignocellulosic biomass (LC) were used as thermal and processing stabilizers for PHB. The thermal stability of both neat and doped PHB samples was studied by rheology and calorimetry. The experimental results showed that neat PHB massively degrades and that the addition of phenol additives enhances the thermal stability of PHB, preserving the polymer molecular weight after processing. This finding was in agreement with the slower decay in viscosity observed through rheological tests. Physical and chemical interactions between polymer and additive were considered as key factors to interpret the experimental data. LC affected the melt crystallization kinetics of PHB enhancing crystallization upon cooling. This finding suggests th...

Lignin and holocellulose from pecan nutshell as reinforcing fillers in poly (lactic acid) biocomposites

Lignocellulose from agro-food biowaste represents a valuable source of cost-effective structural fillers for wholly renewable polymer composites. In this work, pecan (Carya illinoinensis) nutshell (NS) fiber and its structural components, holocellulose (HC) and acid insoluble lignin (AIL), were isolated, characterized and used as reinforcing fillers to manufacture poly(lactic acid) (PLA) based biocomposites. Thermal, morphological and mechanical properties of the prepared materials were analyzed. NS and HC acted as heterogeneous nucleating agents, potentially able to control PLA physical aging. Moreover, they significantly enhanced the viscoelastic response of PLA, mainly restricting the melt molecular mobility due to hydrodynamic effects and the formation of a three-dimensional particulate network. Flexural tests demonstrated that HC induced a 25% increase in modulus compared to the plain polymer. AIL, conversely, conferred higher ductility to the PLA matrix producing an increase in stress and strain at break of 55% and 65%, respectively. Finally, all the biocomposites showed lower resilience with respect to plain PLA due to the lack of chemical adhesion between filler and matrix. These results emphasize the potential of NS as a source of reinforcing filler in polymer-based biocomposites.

From Microbial Biopolymers to Bioplastics: Sustainable Additives for PHB Processing and Stabilization

The term biopolymers refers to a broad class of materials that derive from naturally occurring resources. Biopolymers can be obtained through extraction from biomasses, but also through chemical or biotechnological methods from raw natural substrates. They are used to produce bioplastics, which could substitute fossil fuel-derived commodities. Among them, polyhydroxyalkanoates (PHAs) are polyesters synthesized by microorganisms as energy reserve. The most important member of PHA family is poly(3-hydroxybutyrate) (PHB). PHB is mechanically similar to polypropylene, even though its thermal instability, brittleness, and stiffness hinder its applicability. Improving PHB physical properties can be achieved by blending it with natural additives or by-products of industrial processes. This work takes the form of a case study about the effects of three natural, phenol-based, and polysaccharidic compounds on PHB properties. In particular, data on blending of two PHB matrices with a grape pomace extract (EP), a lignocellulosic biomass (LC), and tannic acid (TA) are reported. The preparation and characterization of PHB compounds and the effects of the additives on processing, thermal and photooxidative stability, crystallization rate, and microbial digestion of PHB are also shown. An overall improvement of polymer processability and photostability, along with changes in crystallization rates, was observed. The study provides evidence that natural additives have the potential for promoting the transition from biopolymers to bioplastics in a sustainable way, both from an environmental and economical point of view.