a b s t r a c t：This work investigated the possibility of using hydrolyzed corn starch–gelatin as a base matrix and cellulose as reinforcement, to produce containers by extrusion blow molding. First, the compounds were characterized by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) to determine their viscoelastic behavior and thermal stability. The results showed that the most suitable processing temperature should be  less

than 120 °C to avoid degradation. Furthermore, the addition of cellulose decreased the

viscosity of the starch–gelatin polymer matrix allowing the compounds to be processed at temperatures as low as 100 °C. Then, parisons were obtained by extrusion blow molding

and presented suitable processing characteristics. Overall, the best containers were found to have 44% higher energy at break and better dimensional stability when cellulose was added.

1. Introduction

Natural polymers processed by extrusion have been investigated for different applications like packaging [1–5]. One readily available natural polymer is starch which is known to behave as a thermoplastic material under specific shear and temperature conditions [6,7]. This is why several investigations were devoted to develop different starch-based products such as extrusion foaming [8–10], compression molding [11–13], injection molding [3,14,15], sheet forming [16–18], and blown films [2,19–21]. In all cases, some additives like water, glycerol, sorbitol, and ethanol, were used to improve melt processability.

However, extrusion blow molding has not been studied yet for starch-based materials because high shear stress lead to degradation (molecular bond break-up) and increasing gelatinization even at low moisture [6,22]. Usually, a polymer can be processed by extrusion blow molding if it has good melt strength, thermal stability, and limited swelling since the parison must withstand its own weight before being captured by the mold [23]. When the mold closes, the parison is cut for air to be injected and parison expansion occurs to be in contact with the mold walls and be cooled [24]. The parison wall thickness determines the thickness of the final part, but other parameters like mold geometry are important where complex relations between different forces (gravity, viscosity, elasticity, etc.) are acting on the material itself. Up to now, only synthetic poly- mers like high density polyethylene, low density polyethylene and polyvinyl chloride have been processed by extrusion blow molding  [23,25–28].

To improve the performance of starch under shear and temperature conditions, proteins have been shown to be effective, especially when the material is extruded [29–33]. Also, gelatin was shown to have good film forming capacity as well as good barrier properties, making it useful for packaging applications like sheets or blown films [34–37]. Gelatin was also shown to improve the elongational [30,32,38] and tensile strength [32] of starch when blended. On the other hand, the addition of cellulose was reported to improve the dimensional stability of conventional plastics [39]. In starch-based polymers, it has been shown to increase the mechanical performance (reinforcing effect) of extruded materials [13,40–42]. Lately, it was reported, using acoustic atomic force microscopy, that recycled cellulose addition in starch–gelatin blends can increase the modulus by chemical interaction between OH groups [43]. In the same way, has been reported that mechanical proper- ties of starch–gelatin blends are in function of starch concentration [38].

Based on the information available in the literature, the main objective of this work is to determine if hydrolyzed starch– gelatin polymer blends, with or without cellulose as a reinforcement, can be processed by extrusion blow molding. To do so, the processing conditions (limited degradation and gelatinization) were first estimated using dynamic mechanical analysis and thermogravimetric analysis. Then, from the results obtained, blown containers were successfully produced and charac- terized in  terms of  tensile properties.