Foam plates made from high (50%) amylose cornstarch were irregular in shape (see Fig. 1) and very heavy because these starches have a high melting temperature, and thus do not give a very elastic paste, which can hold a steam bubble during expansion. Plates made from acetylated high amylose starch had regular shapes and smooth surfaces, baked in much shorter times and had lighter weights than plates made from unmodified high amylose starch. Batter solids levels needed to be at least 36% to make a well-formed tray. Attempts were made to make foam plates using hydroxypropyl high (70%) amylose starch (HP Hylon VII from National Starch), but the plates were not well formed. Visually, the paste viscosity and elasticity of this starch were too low to form an expanded foam using the baking process.
The effects of addition of fiber, PVOH and different hydrophobic agents on the properties of cornstarch foam plates are shown in Table 3 and Table 4. Addition of 5–10% aspen fiber clearly gives higher strength foams, particularly at low and high humidities (Table 4). As shown in Fig. 2, the fibers adhere well to the starch matrix, and thus act as a reinforcement. This is critical at low humidities when starch becomes very brittle and fibers can ‘bridge’ between cracks in the starch. At high humidities, the amorphous starch foam started to become soft, and hence a fibrous network provides additional strength. Baking times increased slightly with increasing fiber content probably because this loose fibrous network increased viscosity and resistance to expansion. Addition of PVOH to cornstarch foams gave some improvement in strength. Further addition of fiber to starch/PVOH foams yielded a plate with high and fairly constant strength versus humidity without an increase in tray weight. Flexibility of cornstarch foam plates was increased slightly by adding PVOH and changed little by fiber addition. Improvement in the mechanical properties of gelatinized starch on fiber addition has been noted by others in extruded films as well as baked foams
แผ่นโฟมที่ทำจากแป้งข้าวโพดสูง (50%) และมีรูปร่างผิดปกติ (ดู Fig. 1) และหนักมาก เพราะเหล่านี้มีอุณหภูมิการละลาย และดังนั้น ให้วางยืดหยุ่นมาก ซึ่งสามารถเก็บไอน้ำฟองในระหว่างการขยายตัว แผ่นที่ทำจากแป้งและ acetylated สูงมีรูปร่างปกติและพื้นผิวเรียบ อบในเวลาที่สั้นกว่า และมีน้ำหนักเบากว่าแผ่นทำจาก unmodified แป้งปริมาณแอมิโลสสูง ระดับของแข็งแป้งต้อง น้อยกว่า 36% ทำถาดที่ถูกต้อง พยายามทำให้แผ่นโฟมที่ใช้ hydroxypropyl สูง (70%) และแป้ง (HP Hylon VII จากแป้งแห่งชาติ), แต่แผ่นก็ไม่ดีขึ้น มองเห็น การวางความหนืดและความยืดหยุ่นของแป้งนี้ได้ต่ำเกินไปแบบโฟมขยายตัวโดยใช้กระบวนการอบThe effects of addition of fiber, PVOH and different hydrophobic agents on the properties of cornstarch foam plates are shown in Table 3 and Table 4. Addition of 5–10% aspen fiber clearly gives higher strength foams, particularly at low and high humidities (Table 4). As shown in Fig. 2, the fibers adhere well to the starch matrix, and thus act as a reinforcement. This is critical at low humidities when starch becomes very brittle and fibers can ‘bridge’ between cracks in the starch. At high humidities, the amorphous starch foam started to become soft, and hence a fibrous network provides additional strength. Baking times increased slightly with increasing fiber content probably because this loose fibrous network increased viscosity and resistance to expansion. Addition of PVOH to cornstarch foams gave some improvement in strength. Further addition of fiber to starch/PVOH foams yielded a plate with high and fairly constant strength versus humidity without an increase in tray weight. Flexibility of cornstarch foam plates was increased slightly by adding PVOH and changed little by fiber addition. Improvement in the mechanical properties of gelatinized starch on fiber addition has been noted by others in extruded films as well as baked foams
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