In the recent years thermoplastic elastomers have gained a great importance for their technical properties and reuse possibility. In particular the styrene-b-(ethylene-1-butene)-b-styrene (SEBS) copolymer has been used to enhance the mechanical properties of polystyrene/polyolefin blends where it segregates at the interface and reduces the interfacial tension. Moreover SEBS functionalized with maleic anhydride (MAH), (SEBS-g-MAH) have been used as compatibilizers of immiscible polymers blends. The grafted EPR-g-MAH copolymer seems to be a better way for compatibilizing a polyolefinic polymer matrix in presence of fillers (e.g. for flame retardant activity), of fiber (e.g. wood polymer composites WPC) and of hot melt adhesives. In industrial scale it is convenient to use some functional polymers with high content of chemically modified polyolefins with MAH (usually called masterbatch), which can be diluted with a variety of different polyolefinic resins (e.g. LDPE, LLDPE, HDPE, PP, EPR) to produce adhesives and multilayer films and composites. The modified-polyolefinic masterbatches with MAH can be readily extruded in other polyolefinic matrices to realize an excellent and homogeneous dispersion of MAH during the blending. These masterbatches are supplied in pellet form in a suitable package preventing moisture absorption and are readily used without applying drying process.
The masterbatch preparation with high content of MAH required:
i) firstly the dispersion in the polymer melt by using a twin screw co-rotating extruder;
ii) secondly a reactive extrusion in presence of organic peroxides, with decompose at temperatures above 160°C such as dicumylperoxide, promoting grafting reactions of MAH on the polymer chains. Unfortunately, some residues of maleic anhydride (MAH) remain in the polymer matrix generating blooming phenomena during the use.
The migration of these residues on the multilayer film surface cause detrimental effects in the case of food packaging applications or for biomedical devices. In fact maleic anhydride is classified to have toxic effect on human health and contact must be avoided. The chemical hazard of maleic anhydride is due its high ability to sublimation generating vapor emissions at the processing temperature.
The existence of free MAH in the polyolefin matrices usually prevent the use of these modified polymers for food packaging applications due to toxicity of maleic anhydride which has the following chemical hazard identification:
a) Potential very Acute Health Effects in case of ingestion or in case of skin contact (irritant) with eyes or skin contact, of inhalation.
b) Toxicity to Animals: Acute oral toxicity (LD50): 481 mg/kg [Rat.]. Acute dermal toxicity (LD50): 2620 mg/kg [Rabbit.]
c) Chronic Effects on Humans: the substance is toxic to lungs, mucous membranes. Very hazardous in case of ingestion. Hazardous in case of skin contact (irritant, permeator), of inhalation.
d) Special Remarks on Chronic Effects on Humans: Exposure will cause asthma, dermatitis and pulmonary oedema; effects may be delayed. Tumorigen.
In contrast, the functionalization, by grafting reaction with itaconic acid and its derivatives, will be applied for the chemical modification of unpolar thermoplastic polymers, such as polypropylene (PP) and polyethylene (PE) and poly(ethylene-co-propylene) (EPR), by thermo-initiated grafting reactions in the melting state in a similar manner above described for MAH. In case of IA or its di-esters derivatives no restrictions are reported for food packaging or biomedical application giving a sustainable alternative to MAH in the industrial scale.
The reactive extrusion conditions will be obtained by a preliminary studies in a closed chamber mixer (brabender-type) monitoring the shear applied stress as a function of temperature and reaction time. The grafting initiator content can be determined as a function of temperature and time for achieving as high as possible IA concentration up to 10% w/w in the polymer chains. This condition can be transfer from a lab scale to precompetitive industrial scale by using a twin screw co-rotating extruder to prepare necessary quantity for technological transfer of modified polyolefin. The brabender-type mixer and twin screw co-rotating extruder and melt viscosity characterization are currently available at APM.
Beneficiary responsible for implementation:APM